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British Broadcasting Corporation Home. Headlands and bays are formed due to differential erosion , where rocks along the coastline are formed in alternating bands of different rock types e. Clay is a softer rock than the sandstone so is eroded more quickly. The softer rocks therefore erode backwards faster to form sheltered bays which may have beaches , whereas the harder rock areas jut out into the sea to form exposed headlands.
As headlands jut out into the seas they are more exposed to erosion by waves. Hydraulic action the force of the water eroding rock will attack cracks areas of weakness in the rock widening them. The cracks will be continuously widened until over time they form a cave as they have been eroded backwards by corrosion rocks in the water hitting off the backwall and eroding it. Continued corrosion and hydraulic action on both sides of a cave leads to it cutting through the headland completely to form an arch.
The rocks at the base of the arch will be attacked by the waves and widened which in time leads to the top of the arch being unsupported and unstable , so that it will eventually collapse. This leaves a column of rock standing alone in the sea which is called a stack. This can be eroded further until it collapses leaving a stump. The direction waves move in is determined by the prevailing wind. In the UK this is usually from the South West.
Therefore waves approach beaches at an angle. When waves break on the shoreline water is carried up the beach at the same angle. This is called the swash. The backwash is when water is pulled back towards the sea.
This happens at right angles to the swash. As a result sand is transported along the beach in the direction of the prevailing winds. This process is called longshore drift. Spits form where the coastline changes direction and longshore drift continue to move material along the beach. Longshore drift will deposit material in the sea after the coastline has changed direction.
Over time the level of the sand deposited will build up until it is above sea level. The beach therefore appears to extend out into the seas and is known as a spit or sandspit. The process of forming a spit can also lead to the formation of a sandbar. If a sandspit occurs near a bay then the spit can continue to form across the mouth of the bay completed blocking it off.
This is now known as a sandbar. The seawater trapped behind the sandbar is called a lagoon. A sandbar is less likely to occur across a river mouth as the river current does not allow deposition to happen and carries the sand out toward the open sea. If a spit grows out across the sea and joins onto an island then it is now called a tombolo, e.
This page is best viewed in an up-to-date web browser with style sheets CSS enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience.
Please consider upgrading your browser software or enabling style sheets CSS if you are able to do so. This page has been archived and is no longer updated. Find out more about page archiving. Headlands and Bays Headlands and bays are formed due to differential erosion , where rocks along the coastline are formed in alternating bands of different rock types e.
Caves, Arches, Stacks and Stumps As headlands jut out into the seas they are more exposed to erosion by waves. More from Physical Environments.
Links Education Scotland A collection of resources from Education Scotland to help you prepare for your exams.
Minimum age of 8 for the boat trip. Minimum age of 5 for the shore based snorkelling. Session times — If you wish to snorkel at both sites you will need to register for both — just not at the same time! Togs, towel, sunhat, warm clothes and lunch. If you have your own snorkel gear you are welcome to bring it along as long as it is fit for purpose no full face masks. Medication if you suffer seasickness best to take first thing in the morning. EMR is providing the snorkeling for free and Norma Jean Charters is giving us a great deal to get into the marine reserve.
Steve will introduce you to these curriculum links and the assignments that you can use and create for your class. Come along to the evening and you will leave with an assignment created for your class ready to go. To book contact Erin erin youngoceanexplorers. Why not grab a Marine Metre Squared kit and go out to discover what lives on your local shore? Sea Week 1 month ago. Thurs 15 Nov from 3. Sunday 4th of November Back up date 25th of November Session times — If you wish to snorkel at both sites you will need to register for both — just not at the same time!
Both changes were performed decades ago based on the resistor style and the orange paper capacitor used for the repairs. Resistors are the standard National-made types with the white ceramic body and hand-written values in blue ink.
Tubes used are as follows: The power pack will also account for a type 80 rectifier tube. The user would then zero the carrier frequency and the modulated CW would be heard somewhat normally. With this method of tuning it was much easier to find weak signals since the carrier was usually easily heard. The RIO uses an output transformer that is a fairly high impedance indicating that hi-z 'phones were probably the intended audio reproducers.
If a loudspeaker was needed then either a hi-z armature-pin loudspeaker or a voice coil-type speaker with a matching transformer could be used. Power-up - When testing the tubes it was noted that every tube was a "U. The tubes had not been out of their sockets in many decades. This could imply that this RIO was used by the Navy.
Not surprisingly, all of the tubes tested good. I also tested a few important components for shorts or continuity and didn't find any problems. I used a National Dog House power pack 6. I connected a set of Navy Baldwin Type C 'phones for audio reproducers. With power applied, the dial lamp came on and within about 20 seconds audio was being received. All switches were noisy or intermittent as expected but AM BC signals were being received. Any switching to either Band A or B resulted in extreme "static" in the 'phones.
If the BFO is on then the AVC must be turned off so any noisy contacts are routed thru the audio system unattenuated - ouch! Even through the RIO seemed to function, it really needed a thorough servicing, especially contact cleaning and alignment. To clean the tuning condenser and the bandswitch required removal of the tuning condenser shield and the bandswitch shield. DeOxit was brushed onto the contact surfaces and the component operated to work out the corrosion. I also lubricated the bearings on the tuning condenser to reduce the drag on the BX dial as much as possible.
The improvement was dramatic. The bandswitch could be now operated without severe noise being generated and the BFO operation was stable. Tuning was light and didn't slip. The switch was a cam-operated finger-contact type of switch that needed cleaning and a slight adjustment for a positive contact. The bandswitch shield removed to show the five section, two position bandswitch.
The procedure starts with Band A and finishes with Band B. Alignment provided a major improvement on both tuning ranges. The trimmers on most of the RF coils needed considerable adjustment to "peak" the test signal. BFO has adjustments on both bands since it has to track the tuned signal. After alignment was complete the RIO was connected to a the ' CF Inv-vee with 96' of ladder line that was shorted together.
This antenna, although not designed as a LF antenna, does a good job as a sort of "T" antenna. Strong signal with clear note. The fact that the RIO does function on almost all original parts after many decades of idle storage and static display is an indication that National used the very best components available in for the construction of the receiver. Of course, the circuit is fairly simple and that also might account for the reliability. Performance - The first thing to remember when listening on the RIO is that there isn't any type of noise limiter or bandpass filters or output limiters, Any pulse-amplitude noise is going to disrupt your hearing when using 'phones for audio reproduction.
The old radio ops always kept the 'phone cups slightly in front of their ears to avoid painful discomfort when listening in a noisy environment. The RIO is very sensitive with the manual specs indications as low as 1uv. But at MW and LF that level of sensitivity is usually lost in the ambient noise. Using a low-noise antenna is a real benefit. The remotely tuned loop antenna provides the low noise necessary to take advantage of the receiver's sensitivity.
Of course, late-spring isn't the best time of the year for testing a longwave receiver but some regional NDBs can be heard. Conditions were terrible with high static levels that sometimes bordered on painful. The next test will be with the loop but the best test results will be those conducted during November through January. This performance information will be updated when better listening conditions allow for a more thorough test. I've been working on the RAA-3 for quite some time now.
I'm hoping to have the receiver operational by the end of the summer of This pound, over three feet wide, behemoth of a receiver has three sections, This receiver is the RAA-3 from It has 14 tubes, 4 individual 2-stage IF amplifiers that are selected by the band switching and a lot more.
This rare receiver was in absolutely horrible condition having been stored wrapped in a tarp but left outside for decades. However, it's restoration is finally coming together.
Radiomarine Corporation of America. The AR was introduced around and was designed mainly for shipboard installations. A matching pre-selector was also included, designated as the ARP. Additionally, an AC power supply was offered, the RM Sometime around , the US Navy wanted to install the AR on some of their smaller ships and a contract was issued for a small number of receivers.
The contract date was just five days before the attack on Pearl Harbor, Dec 2, The CRM receiver uses four metal octal tubes in its regenerative circuit. The RF amplifier, detector and first audio are all 6K7 metal octal tubes while the audio output tube is a 6F6. The CRM uses a 5Z4 metal octal tube for the rectifier.
Three bandswitches - two on the receiver and one on the preselector - have to be utilized for changing tuning ranges. The National Type-N dials are scaled 0 to and have a degree layout. A tuning chart is provided in the manual to correlate the dial reading to tuned frequency.
Coupling, Regeneration and Volume controls are on the front panel and the preselector also has an RF Gain control. Audio output is provided for a single audio stage or for full audio output via two telephone jacks on the front panel. Output is designed for the Western Electric W earphones and, although any Hi-Z 'phones will work, the W phones seem to give the best immunity to noise.
The receiver case is shock mounted and is made of copper plated steel painted a grayish-brown color. The preselector case is made of aluminum and painted to match the receiver although it is not shock mounted. The power supply is a standard steel box painted gray. The front panels of the receiver and the preselector are machine textured aluminum that has been matte chromium plated.
The RF coils are under the chassis. It was setting next to the SX he was going to sell me if I could lift it off of the table. I asked John if he wanted to sell the RAZ-1, to which he replied, "You wouldn't take a longwave receiver away from an old Navy radioman, would you? John lived to the age of 93, becoming an SK in January To my surprise, in the summer of , I got a 'phone call from an estate agent who said that they had found a letter among John's papers that stated that he wanted his radios and parts to be sent to the "Radio Museum in Virginia City, Nevada.
The estate paid to ship the parts and equipment back out west. The shipping of the 22 boxes was spaced out over about a six week period.
In the 21st box was the RAZ Shipping had caused one small problem, one of the largest coils had broken from its mount. The large buss wiring had kept it in place and all that was required was to glue the mount back together and screw the coil form back in place. I acquired the correct shock mounts from N7ID.
I did have to replace the filter capacitors in the power supply for quiet reception. The RAZ-1 is very sensitive and almost any station on LW can be tuned in however the lack of a calibrated dial makes this somewhat difficult if looking for a specific frequency just using the RAZ-1 dial alone for reference. Though I could use a heterodyne frequency meter if it is important to determine the exact frequency being received, I find it is easier to know approximately where I am tuning by listening to known adjacent signals.
I can usually determine an unknown NDB's frequency within 1 or 2 kc by this method. The lack of any kind of limiter is sometimes a problem if local noise is present, however switching to the loop antenna has greatly reduced local noise.
These settings usually result in the best response of signal to noise along with the greatest selectivity. Usually, with several NDBs on the same frequency it is possible to slightly de-tune the loop antenna to one side or the other of the frequency and enhance one or more of the NDB signals for successful copy.
But, it can always be relied upon to pickup whatever is out there as long as reasonable conditions are present. There were a few condition problems that required some unusual cleaning methods to correct. After cleaning the dial the black nomenclature fill was applied using Artist's Acrylic Mars Black.
The receiver panel required a fairly hard scrub using a brass brush and Glass Plus. The panel is chromium-plated aluminum so it can take this kind of treatment and come out looking great. At sometime in the past, someone had tried to install a Squelch control - difficult to accomplish with a regenerative receiver that was designed for a headset output.
Needless to say, the Squelch modification didn't work and only succeeded in the RAZ then having a hole in the front panel. I removed the Squelch modification and installed a red jewel pilot lamp housing with lamp into the panel hole. Now the RAZ-1 has a power-on indicator that looks original and provides useful information - something the Squelch didn't.
There were a few wiring problems in the preselector due to an unnecessary recap job. The original tub caps were checked and found to be in good condition so the modification was removed and everything put back to original. The cases for both units were cleaned with a brass brush and Glass Plus. This removes all of the dirt out of the convolutions of the wrinkle finish and winds up with the cabinets looking very good.
The RF amplifiers use a combination of tuned grid input and tuned plate output using a three-section ganged tuning capacitor.
The antenna switch allows the user to select which receiver will be connected to the antenna - either the AR or an emergency receiver. The audio output can drive the panel mounted loud speaker or headsets either simultaneously or, using the Loudspeaker switch, the panel speaker can be turned off.
The receiver requires a separate power source of which many types were available. These functioned on ships that provided vdc or vdc power. If vac was to be used then the RM Rectifier power supply was used. The AR requires 6. Top of the chassis showing the antenna connections far left front of chassis and the power input connections far right back of chassis. The tuning condenser is under the central cover. Under the chassis showing the bee's wax impregnated coils. The AR could be provided with a cabinet and shock mounts if it was to be used as a "stand alone" receiver.
However, if it was going to be installed into a shipboard communications console as most were then the cabinet and shock mounts were not provided. Many AR receivers were part of the shipboard 3U transmitter console that included a W transmitter, an emergency crystal receiver, battery charger switching, clocks and more. The 5U console had both receivers installed along with transmitters and auxiliary equipment.
The AR was approved by the FCC for shipboard use in concerning minimum radiation from the antenna. The schematic drawings are dated Post-WWII installations were generally on commercial ships. The AR found a lot of use and longevity with some receivers still in use onboard some old oil tankers as late as the s. Unfortunately, most AR receivers led a pretty hard life and the sea environment didn't help preservation.
Most examples have been worked on or have missing parts or non-original parts. The AR shown in the header photo is cosmetically restored with nearly all original parts. The exception is one capacitor under the chassis, the speaker grille and the RCA pointer knobs. I was given the AR shown in the photos as payment for some radio repair work. It probably was taken off of one of the Liberty ships that were part of the "moth-balled" fleet that was moored outside of Benicia, California since the receiver originally was obtained from the SF Bay Area.
The "as received" condition was fairly good considering how the ships were taken care of - they weren't. Of course, the front panel has been repainted in the past - probably with a brush. The perf-metal grille had more than its share of paint applied and it wasn't original either.
The receiver came without any type of power supply the RAZ-1 power unit RM-6 can be used as a power source. This AR required a little bit of work to get it operational. Bands 1 and 2 functioned okay but needed alignment. Band 3 and 4 were non-functional due to broken leads from the coils that are in the plate circuit.
The open coils resulted in an absence of plate voltage to the first RF amplifier when bands 3 or 4 were selected. I had to remove the coils and rebuild them then finishing them off with a re-waxing job.
After reinstalling, bands 3 and 4 had to be aligned. Performance using a "T" antenna of 98 vertical feet running to a foot horizontal section was very good. Since the AR was the replacement for the AR, it's fair to compare the two receivers.
First, with a direct readout dial there's no need for the charts and graphs necessary for finding where you're tuned on the AR The preselector is built-in with the AR Also, only a single band switch is necessary on the AR while two band switches are used on the AR plus a band switch on the preselector.
Sensitivity on the AR is about the same as the AR with preselector. Regeneration action is very similar in that it's a very sharp adjustment between maximum sensitivity either non-oscillating or oscillating and any adjustment below either point greatly reduces sensitivity this is typical of regenerative detectors though. The AR seems to hold its adjustments better across the band especially the Trimmers that only require a slight adjustment from one band end to the other.
This is expected since it's part of the alignment process. I find that the loudspeaker is actually pretty good for some reception. If you want to use Hi-Z phones, it's better if you leave the loudspeaker on. Without the speaker load the 'phones seem to respond to more noise than signal. Any receiver built for shipboard use had to be "bullet and bomb" proof, in other words, the ship had to take a couple of torpedoes, be sinking fast and the radio gear would still be working.
Additionally, steel and iron was kept to a minimum in shipboard radio construction to reduce corrosion problems that were common on marine equipment.
The construction is something to marvel at - so over-built, so heavy-duty with no expense spared - it's no wonder that most RAK or RAL receivers still function with all original parts even though they are pushing seventy years old.
The design concept was to provide maximum reliability in severe service by simplicity of design - and it paid off since the receivers were in use up until the end of WWII with their last service on board submarines. The RAK and the RAL used glass tubes that were large six-pin type, 6D6 tubes for the two RF amplifiers, a 6D6 for the regenerative detector, a 6D6 for the first audio amplifier, a 41 for the audio avc amplifier and another 41 for the audio output.
The power supply, CNV, was a separate unit that used a 5Z3 rectifier, an regulator tube and an optional ballast tube. The can be left out of the power supply if the AC power is stable and noise free. An internally mounted switch routes the vac to a different tap on the power transformer if the ballast is not required. If the ballast tube is installed it will be on regardless if it is used or not although less current is flowing through it when it is switched out of the circuit.
Since the ship had to generate its own power and most of the equipment onboard including motors to rotate gun turrets ran on this power, the varying switching loads are what caused the line voltage fluctuations that required using the ballast regulators. In shore set-ups, on standard AC line power, ballast regulators were not required. The receiver has a low pass filter that is permanently connected in the audio circuit to roll off the upper audio frequency at about hz.
An elaborate audio avc circuit allows the user to limit the audio or noise peaks at an adjustable level. This was to allow the receiver to be used in heavy static conditions. Also a selectable audio bandpass filter was provided to enhance CW reception in noisy conditions. Voice can be received but it is severely limited on the higher audio frequencies making copy difficult. The manual states that another receiver should be used if voice reception is required - like the RAL. The tuning of the RAK is heavy duty, gear driven and the tuning dial readout is shown on two circular dial scales of 0 to 10 and 0 to The actual tuned frequency has to be correlated with a graph that is in the manual.
The receiver does provide a logging chart on the front panel for a "most used frequencies" reference. A frequency trimmer, an antenna trimmer, sensitivity and regeneration controls on on the lower panel of the receiver.
The meters monitor audio output level in db and tube heater voltage. The RAL receiver is almost identical construction but has nine bands covering kc to 23mc.
Additionally, the low pass filter can be switched out of the circuit for voice reception and a vernier frequency control is provided. Most of the concern about a stable AC line voltage was directed at the RAL receiver which itself can become unstable at high frequencies if the line input varies.
Normally, the two receivers operated together through a control box CND that allowed the radio op to monitor two frequencies simultaneously. The control box also could be used to switch the AC to the receivers on or off. I provided for a space of about 3. I ran the power supplies with their ballasts even though wasn't necessary. The actual difference in power consumption is significant - the ballast dissipates about watts.
I had run the receivers both with and without ballasts and I noticed that the received noise seemed to be slightly less with the ballast in use. In actual operation, the RAK is a very sensitive receiver that spreads the LF tuning range over several bands. This bandspread action is nice for tuning in weak stations or trying to separate several stations that are on the same frequency - as many NDBs are. The major problem is that calibration is relying on the readout versus a graph and that graph is in the manual.
The first thing to do is make a copy of the frequency graph to keep with the receiver. Next is to calibrate the RAK so the readout is fairly close to the graph. Then it is easy to keep track of where you are in the LF spectrum.
If it is important to know the exact frequency, I use a heterodyne freq-meter set up. The Audio AVC will help with static crashes and to a certain extent, noisy conditions but, like most output limiters, if it is advanced too far it severely clips the audio with high distortion. The adjustable bandpass filters are almost useless.
This is due to the high frequency chosen for the first audio frequency cut-off - hz. This may have been fine for true CW but that is seldom encountered anymore in the LF bands. The lowest setting of the filter works okay on NDBs but the other bandpass frequencies are even higher in frequency and so are not very useful.
The tuned loop antenna, with its high Q, really helps reduce the noise and increase the signal to noise ratio. The audio output is taken from the front phone jack.
It's Z ohms and, while the RAK will easily drive a ohm speaker, many more weak signals can be copied using earphones rather than a speaker. She's tuning the RAK and is ready to copy on the "mill" the typewriter. Note how she has the 'phones slightly in front of her ears. This helps reduce "ringing ears" from static crashes or unexpected loud "pops" common on the lower frequencies. Army communications set-up for local ground transmissions. The telephone box allowed interfacing a telephone contact through the BC transmitter.
Note that the vernier dial locks are removed from all three receivers. Fixed stations generally used two or more receivers paired with at least one BC transmitter. A typical Army station is shown in the photo to the left.
Note that three BC receivers are utilized with an AC operated BC transmitter the RA power supply is barely visible under the transmitter table.
Most DC set-ups operated on 12vdc from vehicle battery-charger systems. BCN on Long Wave? I have a "rough-condition" receiver that had been painted "metallic" green. I even had it on the work bench once but I lost interest when I saw some "hamster" rework inside. Recently , I obtained another BC receiver that happened to have the scarce shock mount installed.
This receiver seemed to be pretty original and virtually complete. All will require some work and many require a full restoration in order to function correctly. The receiver is difficult to disassemble and this has saved many BCs and s from being modified too much by hams.
Most hams preferred to modify the easy-to-work-on BCQ. Most receivers will be missing the dial lock since this piece often times interfered with the rotation of the vernier knob. It's not unusual to do mostly a cosmetic restoration and have the receiver work with all original parts with the exception of the dual electrolytic filter capacitor located in the RA power pack. Front Panel Dismounting - One of the common problems with any of this series of receivers was present on this BC That is, the plastic dial index that always seems to have warped, cracked and discolored to the point where it's no longer even transparent.
Luckily, I had an excellent condition replacement. Unfortunately, to install the index requires completely dismounting the front panel. I say "unfortunately" because this task is unbelievably complicated by the Army's mechanical design that never seemed to even consider the possibility that the receiver might need to be disassembled someday. Besides the abnormal amount of front accessed screws there are three screws that mount from the backside of the panel that must be removed.
The two fuse holders must be unsoldered and removed. All of the phone jacks and controls must have their mounting nuts removed. The wires to the dial lamps have to be unsoldered. All of the wires going to the front panel "trunk" connector have to be unsoldered. The power input terminal strip has to be dismounted.
All screw connections to Antenna and Ground connections have to be dismounted. Knobs and control nuts must be removed. At this point, you'd think the front panel would easily come off, but not yet! The Fast Tuning gear has a pinned shaft that is flanged. You can't remove the front panel unless the gear and shaft are taken apart and that requires driving out the pin. However, once the gear and flanged shaft are apart, the front panel finally can be dismounted.
A rear view of the chassis showing the stout construction of these receivers At this point, installing the replacement dial index is easy it's mounted with eight screws! Since the front panel is off, now is the time for a thorough cleaning and touch-up.
I use jet black nitrocellulose lacquer that is thinned about 3: After the lacquer has set for a while, I rub down the panel with light weight machine oil. Usually, this will blend the color of the touch-ups with the original black wrinkle paint making the touch-ups invisible. When remounting the front panel, it will be noted that all of the screws are the same length.
However, there are three different length screws. The four long s are for the wire mounts. There are two short s and the rest are all the same length. The two short s are very important. There are two places where, if long screws are used, they will protrude far enough thru the rear panel mounted nut to contact the dial mask with possible scratching of the mask when the band switch is operated.
The "short" screws must be mounted as follows: The other "short" is used near the lower left side of the data plate the screw head almost is contacting the data plate edge. The other observation is the small component board that is mounted to the back of the front panel uses two different length stand-offs.
The reason is that the lower screw must past thru a part of the chassis mounting flange and the top screw doesn't. The longer stand-off is the upper one. Patience is required in any BC,,, rework.
The work is tedious and none of the component parts are easy to access without removing another part or assembly first. Electrolytic Filter Capacitor - Most military gear used oil-filled paper dielectric capacitors as the filters. The disadvantage of this type of capacitor was its large size but the advantage was long-term reliability.
Since space was at a premium in the RA power supply, a dual electrolytic filter capacitor was used. The advantage was a small size for two 8uf vdc caps but the disadvantage now is, after 75 years, the dielectric paste has dried up and drastically reduced the value of the capacitor.
There's ample room to mount new electrolytic capacitors inside the old capacitor can. There are many methods to accomplish this "re-stuffing. This allows the old capacitor to be easily pulled out of the can. I install new capacitors connecting them to the correct terminals and then epoxy the can back together.
I remount the rebuilt cap and connect it into the circuit. The photo to the left shows the underside of the BC and in particular the RA power pack. Note that the RA is "swung out" on the right side hinge mount.
Also note the wiring harness that is connected to the power terminal strip. It's usually only dirt or maybe minor corrosion that is causing the problem. This can be cleaned off using a small piece of Alu-Ox paper or a very small wire brush. It might be necessary to bend the arm slightly to have better contact.
If the AC contacts are damaged beyond reconditioning then the entire switch has to be replaced with a used-good original. These are sometimes difficult to find except from parts sets. The same switch is used on all of the versions of the BC, , and Alignment Notes - IF is Note in the photo above left that the large LO box far left has four plugs that are covering access to the trimmers for each band.
Also note the shield cover over the two RF amp boxes and the Mixer box that is preventing easy access to these trimmers. Each IF transformer adjustment has a lock nut on the threaded shaft to prevent tampering see photo above right showing top of chassis. Other than the lower frequencies involved, the BC is straight forward in its alignment procedure.
This is something like a "T" antenna and it performs fairly well on LF. The test listening was on January 29, from to PST. I only tuned the BCD from kc down to kc. Within the frequency span and time period I tuned in 25 NDBs.
All signals were heard over a headset, not by loudspeaker. BFO was on and stations generally tuned for zero beat of carrier to then hear the MCW tone correctly. The AVC was off. Noise level wasn't too bad and I'd rate the conditions as "very good. The BCD is a capable LW receiver that has ample sensitivity in the medium wave portion of the spectrum using a wire antenna.
There is no crystal filter or any other method to reduce IF bandwidth so many signals are "heard" over what seems to be a fairly wide IF passband. It's easy to select one particular signal and then concentrate on that tone or sound of the signal to then successfully copy the call. Most of the time this process will be with very, very weak signals that are within the passband with stronger signals.
If the received noise seems to be covering up some weaker signals it's possible to slightly "detune" the antenna trim ALIGN INPUT control to reduce the noise while not affecting signal copy. While the BCD is kind of a "basic" superhet with no fancy filters or output limiters, it does a good job with the few controls provided.
Without an output limiter though there isn't any way to reduce "pops and clicks" or heavy static. Wearing the 'phones just ahead of the ears is recommended. The receiver is connected to a pick-up loop that is mounted within the main loop. Test listening was on February 1, from to PST. I only tuned the BC from kc up to about kc.
Conditions were very good. The BCD running with the tuned loop antenna is a surprisingly good performer. Without any bandwidth controls, one would expect noise to be a problem but the loop does keep the noise level somewhat lower than the wire antenna. Additionally, the "loop tuning" provided the ability to slightly detune the peak adjustment which lowered the noise without causing loss of the signal. This was a nice advantage for signals that were "in the noise.
These two features, loop tuning and antenna trimmer, do a lot to make up for the "wide open" IF bandwidth which does have a tendency to be somewhat noisy. As mentioned in the "wire antenna test" section, the BCD is a pretty basic receiver with no filters or no bandwidth control. I don't think any vintage LW receiver enthusiasts will be going out to purchase a BCD to use as their main LW receiver, but I was impressed with its performance and would rate the receiver as one of the better medium wave and low frequency receivers.
Additionally, if you get tired of listening to MCW signals on 'phones, you can always tune in almost the entire AM BC band and listen on an LS-3 loudspeaker - very cool. Though the bandswitch looks like the RAO catacomb system, it isn't. The mechanism uses several large gears to simultaneously actuate two large ceramic switches to provide band changes. Unlike the earlier LW receivers described above, the RBL has a built in power supply and has direct frequency readout on the illuminated dial.
The circuit uses a cascade of three 6SK7 RF amplifier stages. The detector is a 6SG7 regenerative autodyne detector followed by a 6H6 audio limiter circuit followed by a 6K6G audio tube.
Heavy duty construction, ample shielding, copper-plated cabinet under the black wrinkle paint are standard construction used in the RBL receivers. They were normally bolted to a cushioned mount that attached to the holes in the lower front and rear corners of the cabinet. Nowadays these mounts are usually missing.
Included in the circuit is an audio filter for wide or narrow bandwidths switch on left side of escutcheon below ON-OFF switch and an adjustable audio limiter switch and control on right side of escutcheon.
The limiter is very well designed and works wonders in reducing the static crashes while not distorting the audio signal. The direct frequency readout on the dial is the major advantage of using the RBL receivers and the accuracy is impressive considering the receiver's age.
The illuminated dial is quite a departure from the usual military LF receiver. The lower controls l to r are gain, regeneration, bandswitch, antenna trim, oscillation push button and frequency trim.
It required a little work before it was functioning to its specifications. The tubular antenna connection input that attaches to the box that bolts to the back of the cabinet was shorted internally so essentially whatever antenna was connected was shorted to chassis.
Removal of the tubular connector and just running the coax through the box directly to the antenna and ground terminals fixed the problem. Also, there was a soldering job at the audio output transformer that was poorly done. Exactly what the object of the solder job was is not known but it probably was in search of the lack of output that was really caused by the shorted antenna input. Fortunately, no original parts were removed and only the connections to the audio output transformer were moved to incorrect terminals.
We just returned everything to the original connections and then the receiver output returned to normal. The chassis on this RBL-5 is immaculate and all original. RF section is on the right side of the chassis and the power supply, limiter and audio sections are on the left side.
I have logged a lot of NDBs using this RBL-5 receiver, primarily because the RBL-5 is easy to use, very sensitive, has direct frequency readout and the limiter functions quite well. The limiter makes long sessions of receiving comfortable since the static crashes are reduced to the point where they aren't causing headaches anymore. I take the audio output right from the earphone jack on the front panel running ohm 'phones for best copy on weak signals.
The NBDs normally copied are multiple stations operating on the same frequency, with two and sometimes three different CW identifications being heard simultaneously. The RBL works particularly well with the tuned loop antenna and this provides the ability to add some directional characteristics to the reception.
Additionally, the loop can be slightly de-tuned to allow enhancing NDBs that are on one side or the other of antenna resonance which can sometimes help with copy. The underside of the RBL-5 is also immaculate and all original. The photo shows the multiple gears that drive the two ceramic bandswitches. Construction is first rate as expected from National Company. Note that the alignment trimmers are all clustered together. The bottom cover has a sliding access panel that allows the receiver to be aligned with the bottom cover installed - probably why the RBL-5 has such an accurate dial readout.
Shown in the photos right and left is the Wells-Gardner Co. This receiver is also in excellent condition. Typically, W-G used mostly National parts but did use their own transformers, chokes and smaller components. Using a TRF with tracking BFO was advantageous in keeping the leakage radiation on the antenna to a very low level that prevented enemy direction finding equipment from determining the location of the receiver.
Additionally, the low-level of radiation allowed the receiver to operate in the presence of other receiving and transmitting equipment along with radar equipment without interference. The tracking BFO design utilized a section of the main tuning condenser so the BFO tuning condenser was ganged to the main tuning. Since the new receiver was not a superheterodyne, the BFO had to track at 1kc above the tuned frequency allowing a 1kc heterodyne to be heard thus allowing CW to be readily copied.
There were a couple of very good reasons for not designing the new LF receiver as a superheterodyne. First, was to provide complete coverage of the tuning range of 15kc to kc. Most IF amplifier sections utilized around kc to kc for the intermediate frequency, right in the middle of the most used portion of the medium wave band as far as the Navy was concerned. Operation of the IF amplifier at, for example kc, would eliminate a section of frequency coverage of about 20kc either side of the intermediate frequency.
Some superhet LW receivers moved the IF above the intended tuning range 15kc to kc but there were disadvantages to this solution to the problem. For example, the RBH receiver uses an IF of kc but any transmitting activity around kc will "leak into" the IF section of the receiver and cause heterodynes throughout the tuning ranges. The power supply will easily operate two RBA receivers for emergency conditions and two separate connectors are provided.
Internally, all versions of the RBA receiver circuit are the same. The underside of the RBA-6 chassis. Full shielding of each RF section is provided when the bottom cover is installed.
The heavy-duty band switch uses ceramic mounts with. All components are mounted on terminal boards or are mounted directly to the chassis. Tracking BFO is the front section of coils. The rear-most set of coils are the Antenna Input coils. The RBA-6 shown is from a contract. This version is identical to the RBA-5 internally but the RBA-6 is a rack mounted configuration only and is painted smooth Navy gray rather than black wrinkle.
Judging by the condition of this receiver, it is unlikely that it was ever put into service. It is all original except for the substitution of an SO UHF connector in place of the Navy coax connector for the antenna input. The RBA-6 is an impressive performer with ample sensitivity, direct dial read-out with illumination and a tracking BFO rather than regenerative-autodyne detector. The dial accuracy is excellent and allows tuning the NDBs by frequency rather than constantly referring to charts or graphs.
The LP filter does limit the audio frequency response on BC stations but not to the point where the voice is incomprehensible. The RBA-6 is a first-class longwave receiver capable of receiving any of the signals found below kc if used in an RF-quiet area with an appropriate antenna. RBA-6 Performance - I have been using this RBA-6 during the morning hours for late September through most of October and have found the receiver to be a phenomenal performer.
That's amazing selectivity for a TRF receiver. The wire antenna I'm using is the ' center-fed dipole with 43' of open feed line that is shorted together at the receiver antenna terminals. This antenna, while not really something I designed for LW, seems to work quite well with all of the LW receivers. JJY also can be received every morning on 40kc coming out of Japan. Noise is the only limitation on reception and for better noise reduction I have to run a loop antenna.
This photo of the U. Mugford in January 21, - I finally got the RBA-6 up to the top floor of the house where it can be used with the six-foot loop antenna. I had tried using the loop antenna in the basement but the concrete floor and the rock foundation were a serious detriment to the loop's performance. The top floor of the house is actually about 30 feet above ground level and allows the loop to function quite well even though it is located indoors.
The performance of the RBA-6 on the loop is amazing. The signals just jump out of a fairly quite background noise level. Much quieter than running on the wire antenna. Most frequencies seem to have at least three NDBs active and by tuning the loop I can usually enhance one or the other to allow copy. Quite an improvement in performance.
November 7, - QTH is now Dayton, Nevada and the antenna is a foot long end-fed wire up about 50 feet. This antenna works quite well with the RBA-6 although the noise level is probably higher than using the loop.
However, the actual ambient noise level is so low in Dayton that the ft wire seems to provide better signal levels than the loop ever did in Virginia City.
More info to come, There are additional changes internally. Additionally, like many receivers that have gone through a field rebuild, the cabinet is black wrinkle it is for an RBA-1 while the receiver's panel has been repainted gray.
This RBA-1 was traded off in It was shipped to Nevada via UPS. No damage was sustained during transport. I purchased this particular RBA-1 because it was the first all-original, black wrinkle finish, complete example that I had ever come across. That is, most have the Field Change modifications and have been repainted gray. For example, the DB meter glass was cracked to several places.
The meter, however, worked fine. Band switching from Band 1 to Band 2 was normal. To Band 3 felt rough, like fine gear teeth meshing and switching to Band 4 was stiff but it would switch. All toggle switches seemed to function okay. There was a little bit of dial drag on the logging dial which was slightly rubbing against the housing. Inside was very nice with all shields present. Some very minor corrosion in just a few locations - nothing serious.
Even the antenna input was still the original Navy coax fitting. Cosmetically, the cabinet was very scratched up with quite a bit of paint missing, especially on the top. Front panel was very good with some minor blemishes and old touch-ups. The dial mask on Band 4 needs some attention as there are some "pin points" of corrosion present. All knobs were present but the spinner was missing from the tuning knob.
The two nomenclature panels were in good condition. All tags were present and in good condition on both the panel and cabinet. Fortunately, I had a spare and a spare cable to apply power to this receiver. Normally, I wouldn't apply power without a thorough check out first, but the seller told me he had the receiver operating, so there was some confidence that nothing serious was going to happen.
I did check all of the tubes first and ended up replacing three. I had a Z ohm modified LS-3 connected to the phone jack on the front panel. However, when switching to Band 3 the output was nil, same for Band 2.
Switching to Band 1 the receiver again had output. Note the bubble-wrapped tubes piled up on the RF coils. Some of the cabinet can be seen to the right. This photo was taken before the power-up test. The most serious problem is the non-operative Band 2 and Band 3, however since the receiver works on Bands 1 and 4, the problem is certainly in the RF stages ahead of the detector. Additionally, repairing the mechanical issues of the band switching "roughness" and logging dial drag will be necessary.
The DB meter glass repair will be accomplished by replacing the entire housing - it's a Weston Type and they're common. Finally, when fully functional, a complete alignment. Cosmetics will be necessary too but that looks to mainly consist of cleaning and touch-up. In order to repair the logging dial drag, the rough feeling band switch and restore the dial mask, I had to access the cast metal housing that has the dial, the dial mask and the band switching inside. The only access to into this housing is from the front and the entire front panel has to be dismounted to even see the front of this housing.
To get the front panel off I first removed all of the knobs. All controls that have panel nuts needed the nuts and washers removed. The bottom cover needed to be removed. Then the two chassis-withdrawal knobs needed to be removed. The meter covers needed to be removed so the meter leads could be disconnected. The meters can stay mounted to the panel. The tuning chart frame needed to be taken off. The screws underneath mount a resistor board to the rear of front panel and these screws had to be taken out.
The PHONES jack nut has to be removed and the shield around the phone jack itself has to be dismounted by the four screws on the side of the chassis. The dress nuts and the hex nuts that mount the four toggle switches had to be removed. I had to dismount the housing around the logging dial. Underneath there are two set screws that mount the logging dial to the tuning shaft. I loosened the set screws to remove the logging dial.
The spacer around the band switch shaft had to be removed. Now came the difficult part, These had nylock nuts on the inner chassis side. Two nuts are difficult to access because of the harness prevents seeing the nut but it can be done by "feel. On the right side, two screws had nylock nuts and two had pem nuts. When loosened, then the red jewel front could be unscrewed and dismounted. Now the front panel could be removed.
Photo right shows the RBA chassis with the panel removed. All removed parts were "bagged and tagged" in small plastic bags. This "bagging" method is extremely helpful to prevent loosing any parts and for easing reassembly. The front part of the housing was mounted with four screws. The next step is to remove the four screws and lock washers that mount the front cover of the housing. Now the front cover can be removed and this exposes the tuning dial and the band switch arced gear.
The dial mask is mounted to the front cover. In addition to the dial mask there is also a gear on the back side of the mask that engages the band switch arced gear and actuates the band changing function. However, since the mask needed to be restored it had to be separated from the front cover.
This required removal of the retaining collar that was mounted to the band switch shaft. The set screw wasn't a hex like all the other set screws had been. This set screw was a spline or Bristol-type. Also, just to make removal difficult, the collar was pinned to the shaft. This required driving out the securing pin with a proper size punch. If done correctly with the proper tool, the pin comes right out. The collar has to be placed on a large vise that has the jaws slightly open.
With a long thin diameter punch, the pin can be driven out. The set screw was only to keep the collar in place while the pin hole was drilled and the pin driven in.
It doesn't have much of a purpose now and was easy to loosen. This allowed the collar to be removed and the dial mask, band switch shaft and drive gear could be separated from the front cover. Painting the Dial Mask - Once the dial mask was removed its condition seemed a little worse than I thought. The minor flecks of corrosion were numerous but most of them seemed to be around BAND 4. I removed the black paint with stripper and wiped everything down with denatured alcohol.
I worked over the surface with steel wool to be sure it was smooth and no blemishes would show when repainted. I used Krylon Flat Black for the paint as the initial coat. Restoring the Mask Nomenclature - Of course, painting the dial mask covered up the frequency band nomenclature. These letters and numbers are embossed so they are somewhat higher than the flat surface of the mask.
To restore the nomenclature requires carefully removing the paint just from the top surface of the letters and numbers. I had to do the nomenclature recovery in two steps.
After the initial paint in flat black, I used a special angled tool that I made that could hold a very small piece of grit Al-Ox paper. This was used to carefully remove the paint just from the nomenclature. Of course, there was some slight scuffing and other minor blemishes that happened to the paint surrounding the nomenclature. The next step was to carefully cut masking tape pieces to exactly cover only the nomenclature.
It sounds time-consuming but it only takes about 25 minutes to do. Next, I applied a coat of Satin Black, which is much darker black than flat black. When this paint had dried, I removed the masking tape. Now, only very small areas between the letters and numbers had the flat black paint showing. These areas were so small that I touched them up using a "ultra-fine point" Pilot pen with black ink. The entire mask was then wiped down with a clean cotton cloth to even out the paint surface.
It sounds like a lot of work and it is fairly time-consuming but the results are worth the effort since the dial mask is quite visible, directly in front of you, on all bands, whenever you're using the receiver. Oct 19, Dial Mask and Band Switch Reassembly - I put a small dab of grease on the mask shaft and installed into the front cover of the housing.
The washer and collar were then installed onto the shaft and the collar pin installed. The spline set screw was tightened. The band switch was set on Band 2 so the mask was rotated to show Band 2 also.
The front cover was carefully placed in position and moved slightly until the gears meshed while the mask remained showing Band 2 centered. The four screws were installed. The adjustment for the gear mesh clearance is accomplished by moving the front cover upwards reduces mesh and tightening the screws. Testing switching showed that the mesh was correct as the switching was ultra-smooth and not binding.
Dial mask after restoration Front Panel Restoration - This is really just a thorough cleaning with a brass wire brush suede shoe brush and Glass Plus to remove all dirt, grime and cigarette residue. The original wrinkle finish is very tough and can take this type of cleaning but you can't be real aggressive.
You just want to remove the dirt not the paint. The front panel had been stripped of all tags and the two dial covers. The silver engraved nomenclature needed substantial cleaning. The front panel must have been pretty dirty as it took about five cleanings until the paper towels didn't turn gray with dirt and stayed fairly white. After this many cleanings, the nomenclature was very legible now. Next is the touch-up. I've been using jet black nitrocellulose lacquer for the last year or so.
This method replicates how the USN did "touch-ups" on equipment that was being repaired but was not in the depot for an echelon-type rebuild.
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