JRC NRD515 HF Coms Receiver, 1982, FM on VFO?

[Radio1950]

Are there any others with detailed knowledge of the JRC NRD515 HF Coms Receiver?

I would like to exchange some findings and notes, especially about FM on the VFO, manifesting as FM on a received carrier, and observed as FM on an AF tone when the receiver is in SSB, CW or RTTY mode.

I was checking the performance of my receiver, and on the last test, which was AF distortion in the various receive modes, and by just using a visual method of observing the AF output on a CRO.
Distortion on AM mode was fine, less than 5%.

But I noticed some FM on the audio when in USB or LSB or CW or RTTY modes, and it was audible in the speaker as a very slight “warble” on tone.
You cannot notice this effect when receiving speech in SSB or on CW (except maybe with continuous key down). I had never noticed this effect before, and I have used the RX quite a bit over the years.
I cannot find any specific web references.

The amount of FM on the audio is such that with a 1 KHz tone as audio output, and whilst observing ten cycles across a whole CRO screen, the last cycle would cover half a division, and with a low deviation frequency, ie not so much with a visible high speed blur, but with a quite regular jitter.

I have carefully checked the alignment of the NRD515 receiver, and its performance is as per specification.

I have tried the test on a second NRD515, and the same effect is present, but maybe a little less.

I have done quite a bit of work to determine if a fault exists, but I am left with the question of whether this amount of FM is normal, and that is what I would like to discuss with other owners of this receiver.

Comparison with different brand receivers is useful but doesn’t tell me if something in my receiver is faulty or degrading. Also, comparison with other receivers is not useful, if that other receiver doesn’t use very similar circuitry to the NRD515.
My iCom 7600 doesn’t exhibit this effect, but uses different VFO circuitry, and hence is not all that relevant.

JRC used similar VFO circuits for the previous NRD505 and later model NRD525.


This receiver is acknowledged as one of the best HF receivers ever made in its day, from about 1981.
It is extremely well made, has good specs, and is a joy to use.

Along with its predecessor, it was also one of the first to use PLL oscillators and LED digital displays, in a receiver aimed at the professional market.


The JRC NRD515 is a HF double conversion superhet and uses a first IF of 70MHz and a second IF of 455 KHz.
It then use a basic diode AM detector, and a four diode bridge type product detector for SSB, CW, and RTTY.
The first oscillator (in a basic description) tunes 70.555 to 100.555 MHz in thirty steps of 1 MHz, and with dial increments of 100 Hz.


I can heterodyne my receiver’s first local oscillator with a good RF sig gen in an external DIY basic diode mixer, and see the FM present as a mixer output.

If I use the sig gen instead of the receiver’s internal local oscillator, I see no FM on the RX AF output.

The FM appears to be coming from a 2.455 MHz PLL VCO, TR4 on the Synthesizer Board, and which feeds the first local oscillator, after some more mixing.

I have checked the VCO drive volts to have no spurious signals, and all power supplies are good with no hum on the DC rails.
Handbook gives no real info here.

So, does anyone have experience with this receiver please?
Do all NRD515 receivers exhibit this “effect”, and to what degree?

[Radio Wrangler]

What you're seeing is usually called phase noise. All receivers have it, to a degree. There is a view which says that oscillators cannot make sinewaves, they can only make filtered noise. The difference between a good oscillator and a bad one lies in the tightness of the filtering.

Any FM or PM sidebands on the local oscillator of a receiver are transferred onto every signal passing through the mixer. The effect is to broaden the skirts of your selectivity beyond the shape of your filter as far as unwanted signals go, and to make the wanted signals noisier.

The tuning line to the varactors in a VCO is hellishly sensitive to any noise getting in. low noise components are very desirable. You'll see the tuning signal goes to the varactor via a resistor, sometimes substantially higher in value than is optimum before designers learned of the tradeoffs. It may be helpful to put some true low noise parts in these places in your VCO. Use metal film, their noise is pretty much right down at the thermal floor. You don't want carbon film resistors, they are actually several dB noisier than this. Carbon composition are even worse. Incidentally, the usual thick film resistors used in surface-mount construction are either Ruthenium Oxide or Tantalum Nitride and exhibit noise around 20dB worse than metal film.

You may have a part which has degraded, an opamp or transistor. There are a few things you can do to improve these things. They were one of the best receivers on the amateur market of their era, but they were not in the same league as some of the things being made by Watkins-Johnson, R&S etc for government agencies. They dd get used by such people for their less demanding needs.

Watching the jitter over multiple cycles of SSB demod audio tone is actually quite a sensitive test.

Are you sure your signal source is unimpeachable. is the first question to answer. Forget most sig gens, a good quality crystal oscillator is the best bet.

THere's a lot on synthesiser phase noise, architectures and circuits in the books written by Ulrich Rohde (son of the Rohde in R&S). he wrote a good approachable text on synthesisers, and then brought out newer versions with updates as things moved on. I get a mention in the most recent one so I might be biassed.

If it's got worse, and it is worse than other examples, then I think you've got a degraded component. A resistor, transistor or IC. The only way you'll find it is by substitution. Various tests may get you into a particular block, but not all the way to component level.

David

[Andrew2]

I take it the FM is random, low frequency wobbling rather than any recognisable tone? In the past, I've had the 'random wobbling about a bit' effect on homebrew PLL's and in most cases it has come down to very slight perturbations on the power supply, mainly due to my 'oh that'll do' design philosophy. Further stabilisation and decoupling usually fixes it. I can definitely recommend another careful look at the supplies to the PLL and VCO circuitry. Loose screws can be murder....

[Radio Wrangler]

There are some rather dodgy Japanese trimmer capacitors which might be in the VCO circuits. They suffer from tarnishing/corrosion on the sliding contacts at their hub. Icom did the worst thing by slurping an anti-microphony goo all over their VCOs and used a material which attacked the trimmers. These pulled the VCO until it went out of lock rather than creating noise, though the effect was rather noise like as it was failing.

David

[Jon_G4MDC]

Good evening, I have another Bible quote thanks to David.

"There is a view which says that oscillators cannot make sinewaves, they can only make filtered noise."

It is just what they do. What a wonderful way to view it.

[turretslug]

Indeed! A selective noise Q-multiplier.

[Radio1950]

Thanks for replies.

I am still hopeful of a reply from another owner with comments on this effect in their receiver.

Wrangler – thanks.
My RF Sig gens are Marconi 2018 and 2022, both give same results with FM on AF output, and no FM when substituting sig gen for RX Local Oscillator 1, or for “VFO IN”.
The sig gens are quite clean when received on my iCom7600.

I am almost certain that the FM effect is coming from the 24.550 MHz VCO, around TR4, which is divided by ten to give the Digital VFO of 2.455 MHz, which JRC also use to provide “VFO Out” for an associated TX, or to mix with 70 to 100 Mhz to give the LO1 for the RX first mixer.

If you look at the area of VCO drive volts in the attached cct, I have replaced C82, C83, C316, and tested all .01 mFd decoupling caps nearby.
Removing C316 gives some improvement, as does placing a 10 M resistor across C83, a design characteristic which is used with all other VCOs in this RX.
I suspect that JRC is using the internal loss resistance of the C83 and C316 TAG capacitors as “anchor resistance” to ground.
Other circuits use 5M or even 100M here.
I have replaced C316 TAG with a ceramic type.
TP9, VCO Drive Volts, is very sensitive to test probes.

Andy – thanks also.
I have checked the main RX DC supplies and filter caps as OK by ESR test and by using known good tested caps in parallel.
The PLL and VCO have a separate subsidiary +15 to +12V voltage regulator IC33 (LM723) and I have also placed additional electro caps across the IC33 supply in and out, and have not noticed any change in the FM effect.
If it was due to stuff on the DC supply, I would have thought that I would see a change here, but no.

It is not all that easy to change components in this area, as the whole board has to be removed to access the VCO which is in a shield, and which is attached with bottoms screws.

Additionally, I didn’t want to change components just to experiment or reduce an effect which is possibly normal in the degree observed, and cannot be reduced further.
My receiver is quite pristine.

Tests of AF distortion when on SSB Mode reception are sometimes never done, even with high end receivers such as WJs et alia.
The NRD515 Manual does not give test figures, only for AF distortion when in AM Mode.
NRD515 RX stability test figures refer to receiver local oscillator performance, and as seen in stability of the RX with received signals.

I may be concerned with nothing here, but it is worth raising the subject.

Attachments are the circuit in question, in PDF form to give a larger “view” of components, and a second doco which is a cut down PDF of the receiver, with just the ccts, for your possible interest.

Thanks for reading.

[Radio Wrangler]

It's a two-loop synthesiser with only a divide by ten reduction between them, so the reference frequency at the PSD of the lower significance loop (Not legible on the diagram, I'm afraid) will be only 10 times the step size of the overall receiver.

This makes it a very slow loop, leaving the noise of the VCO pretty much uncancelled. I expect it to be fairly noisy.

If yours is worse than others you've seen, itmay just be manufacturing spread in devices used, or you may have something degrading. I'd go for making phase noise plots of the suspect oscillator isolated from the rest of the loop, with a very low noise voltage source driving the tuning line if I wanted to investigate this by measurement. Substitution may be somewhat easier.

Sig gens: a lot of them switch to a mixed down architecture for their bottom band, nd this doesn't reduce phase noise. The best known exception to this is the HP8640A/B which uses a cavity oscillator and divides all the way down to 500kHz.This can be used in a homebrew phase noise test setup. If you've got an ARRL handbook 1995 onwards, I put the description of how to do it in the oscillators/synthesisers chapter.

What you're seeing ay just be what's typical of a synth of this era. The JRC receivers were amongst the best amateur gear, but it was their prime performance limitation. There were some real stinkers from this era. The FTONE was abysmal. THe Kenwood TS930 and 940 got modified by their UK importer (if you paid extra) to fix an embarrassing bit of lousy design in the PLL timeconstants!

You're right, examining another example may be the only way to decide if you're tracing a fault, or that's just the way they are.

David

[Steve G4WCS]

It may be worth also going through the electrolytic caps assoiciated with power supply decoupling, these are showing their age now ( just been through this with a kenwood TR-9130 that had a low voltage on the control board ).

as an aside, years ago when I worked in calibration, at the back of the lab there was a small room belonging to air traffic control containing one of these with the matching transmitter, feeding into an HF log periodic outside, purportedly for talking to the Tornadoes on Ferry Flights, despite me as an apprentice doing a test that proved that HF SSB couldnt be used during the flight, as it played havoc with the flying control surfaces...

I often wonder whether they are still sat there to this day, or whether they were decommissioned and squirreled away by one of the ATC engineers ( most of which were licenced hams ).

I also managed to rescue and repair some great pieces of RF test gear including an HP 8640B sign gen which mainly needed the big multiway rotary swich having the contact fingers re glued on. When I left that job I had to bring all my gear home, and had a big clear out when I wasnt going to play radio anymore, of course I regret this now as yes, Im playing radio again

[Radio1950]

Investigation continuing.
Thanks for suggestions.

Sorry about that previous blurry block diagram.
Attached is a better copy, and another from a JRC brochure.
Forum attachment limitations.

The block diagrams don't show some details.
For example, the 70-100 MHz VCO is actually a cluster of three physical VCOs, selectable in "bands" 0-10, 10-20, 20-30 MHz, to overcome the limitations of VCOs over too wide a freq range.

And Walter G. has a heap of info on his public website, and I acknowledge his very good website and his help.
https://people.zeelandnet.nl/wgeeraert/index515.htm

[Damien VK3RX]

I had a NRD515 some 15 years ago, along with the separate memory unit.

I recall on arrival it had somewhat muddy audio, and the problem was the Kokusai filters. More about that at the link below. When I opened them up they were gummed up as expected, and a rebuild per the instructions got rid of that problem.

http://jlkolb.cts.com/site/koku.htm

[G0HZU_JMR]

Are there any others with detailed knowledge of the JRC NRD515 HF Coms Receiver?

Sadly, I've never used one of these receivers but I do have some synthesiser design experience. I did a lot of synthesiser design in the 1990s at work across LF through several GHz and I have experience of the possible tradeoffs in an old school design like this. I've looked over your circuits and the block diagram and I can offer advice on what phase noise performance you might get from a healthy example? I can also advise on what aspects of the design look a bit strained and which areas are likely to cause it to be a bit noisier than a theoretical model of the synthesiser?

Obviously, it's best to focus first on the 2.5-3.5MHz Digital VFO section because you appear to have isolated the issue to here but would you be interested in a basic model that can predict what to expect from this overall synthesiser? I'd be a lot more confident if I actually had one of these receivers here to play with but maybe the initial (but very crude) design model I can offer may be of some use?

[G0HZU_JMR]

The other thing I wanted to add was a suggestion to try and capture the audio out of the receiver with a clean RF test tone from the Marconi 2018 and the receiver in SSB mode. This way we can all get some idea of how significant the issue is. Can you feed the AF out into a PC soundcard and capture a .wav file? It would only have to be of a few seconds duration and the data could be post processed on a PC to look at the spectrum. Also, you mentioned mixing down the Digital VFO to an AF frequency with the 2018. Can you also feed this AF output into a PC soundcard and capture a .wav file? It would be interesting to see the response, especially if this second test was mixed to maybe 10kHz into the soundcard. The wav file could be uploaded to the internet for us to download and play with.

At a CF of 2.5MHz the close in phase noise of the Marconi 2018 (at offsets below a few kHz) will be very low and it should be much lower than the close in phase noise of the Digital VFO so this should be a valid test. The Marconi 2018 should be a lot cleaner than the little Marconi 2022 here so best to use the 2018 rather than the 2022 if you have the choice.

[Radio1950]

Firstly, some answers to questions and suggestions.

Andrew2
The effects as observed on a CRO with 1000 Hz demodulated AF tone are a mixture of, a little noise, a little 50 Hz AM maybe 1-2% and hard to discern, and some FM which appears to have a deviation of approx +/- 50 Hz, and at a mod freq of about 80 Hz (hard to specify).
The FM is the larger effect.
It is "heard" as a very slight warble in the speaker.
On a CRO it is regular, not a "wobble".
The effect is not noticeable on received SSB speech nor on CW.
It is a very small effect, and I wonder why I pursue these things.
I don't have a CRO photo of the original symptoms anymore as the receiver has some replacement caps.

Wrangler
The RX is renowned for quite low noise.
Your suggestions of essential reading for PLL and VCO are good, and especially those about using low noise components are backed up by reference material which I have read.
This is also good -
https://www.nxp.com/docs/en/application-note/AN1282.pdf

Steve
Read my next post re caps.

The history of this particluar receiver is that a batch of about thirty was purchased in Australia for monitoring aviation HF SSB air ground coms, and also for monitoring aviation NDBs by both operators and techs.
Operator's prime SSB equipment were fixed duplicated rack and floor equipments, the NRD515 was backup.
The agent (VICOM I think) modified the mains wiring to make it compliant.

Damien
Some receivers have Kokusai filters which have the degraded foam, and which drastically reduces sensitivity on 2.4 Khz selectivity, and increases audio distortion.
This is fixable.

The receiver has also a reputation for high AF distortion on AM (only) with a simple diode detector "loading" the IF, and some users have included an isolating amp to reduce the problem.
My receiver has less than 5% distortion on AM as determined by visual means on a CRO (if you can see distortion, it is more than 5%).

Jeremy G0HZU
Thanks for comments and kind offer.
I keep reminding myself that this was a 1980 receiver, probably based on an early 1970s design (eg NRD505 et alia) and not to expect too much from it all.
As Wrangler said in an earlier post, and I now agree with, this receiver was aimed at Marine, Fixed Coms, and the amateur market, and budgets had to be kept, although it is mostly very well made.
That's a very kind offer re the audio file.
I have changed some components now and don't want to go back to original.
But I will see if I can save a file.

Both Marconi 2018 and 2022 give visibly similar results.
.

[Radio1950]

.
After some more reading, including the forum suggestions, I have again checked the most likely components to be contributors to this FM effect.

I removed the shields around the VCO and tested relevant components.

Referring to the attached part circuit of the Loop 2 24 Mhz VCO, I have tried many arrangements of components around the area of the Mhz VCO input filter, which is prime suspect.

For ref, IC34 is an MC4044 (not a CD4044) phase freq comparator, pin 1 is Ref input, pin 3 is Variable input.
IC36 is a 4016 as a pump, VCO is TR4.
IC33 is a 723 regulator just for this VCO, providing +12 V off the +15 DC.

Firstly I changed C42 and C44 in the DC supply regulator section using new Low ESR individually checked caps.
There was a very slight improvement.

I experimented with removing C82, C83, C316, and replacing one at a time with various types, even using MKT, as I really am suspicious of TAG Tantalum caps in sensitive circuits.

I have achieved the best results and reduced the effect, by replacing C83 with a new ceramic, and replacing C83 and C316 with new TAG caps, each tested for capacity and leakage, and by adding an extra small 10M metal oxide resistor across C316 to act as a “VCO volts earth anchor resistor for DC”.
All new caps have original values.

The resistor gave the most improvement.
I suspect it swamps the leakage of the VFO Filter tantalum caps to more positively hold the DC volts steady, but doesn’t affect the VCO slew rate too much.

The FM effect is now reduced as far as I can easily achieve.

JRC themselves changed the value of C316 from 1mfd in earlier receiver versions to 4.7 mfd in mine, so they must have had review feedback or design second thoughts.

I still do not know how these residual FM effects are being produced, but I suspect ground loops or PCB track interactions, in which case further improvement is difficult. I did some experiments with additional earth straps and shielding “plates” to no avail.
The Australian importing agent, VICOM I think, rewired the mains for compliance, and routed the mains wiring to the ON switch in shielded twin between the two flat chassis plates, and close to the VCO.
I rewired this along the RHS chassis frame, but to no improvement.

When I was checking my own PCB solder joints with magnifying equipment, I was a little surprised to find that JRC did not clean the board very well in some areas, with a little soldering debris in some areas, and now under PCB lacquer. The board and construction quality is otherwise extremely good.
I was especially looking for PCB leakage resistance problems in the area of the VCO filter components.

Two NRD515 receivers here exhibit the same effect, although with slightly different results, which is why I originally asked for feedback from other owners.

I am satisfied now with my receiver, and will move on.

Anyway, as I continually read in literature about PLL and VCOs, “It’s all about the filter!”
.

[Radio Wrangler]

The NRD515 was one of the quietest receivers, in terms of synthesiser noise, on the amateur market of the time, but at that time the overall standard was fairly poor.

In terms of most performance parameters, the early transistorised HF receivers had been a significant step backwards from what the best of the valved designs could do. It took some time to learn what we'd lost and to evolve tougher mixer and amplifier designs to be able to put intermodulation distortion back to the performance the HRO achieved in the 1930s. In this area, the NRD515 was one of the best ones on the amateur market. But not everything in the garden was rosy, ARRL reviews in QST started showing dynamic range measurements and third-order distortion product levels with the words "Measurement limited by receiver phase noise". As we fixed one problem, it revealed the next limitation. It took some time for the amateur market to come to terms with the need to do something about it. The fancy synthesisers had fixed the drift problems of VFOs, but were performing significantly worse in other ways.

Australia has a big bit in the middle where aircraft are out of range of VHF comms service, so HF SSB is very important. It is inot surprising that the idea of using squitter transmissions from aircraft transponders with 1090MHz receivers in ground stations en-route instead of building full mode-S SSR radar stations first arose in Australia (The Americans, are claiming it as you might expect). So there would need to be rackfulls of MOPS-compliant receivers at the ground stations tuned to the channels in use and to the back-up frequencies. The NRD515s would have made an effective emergency backup to these and allow the system to be monitored for about a tenth the cost of MOPS-compliant receivers. Spooky organisations quite liked them too. Their budgets may be secret, but they didn't want to leave a visible hole in their country's accounts and thereby draw political attention. They really went for Icom R9000s when they came out. Not quite Watkins-Johnson performance, but they could afford to use a lot of them.

On the professional front, phase noise limitations were well understood. Marconi printed their notorious article on HF receiver reception failure factor by B M Sosin. It included a survey of the many professional HF receivers of the day and the star of the show was the Marconi H2900, whose design had been led by one B M Sosin! No surprise. It was a very good receiver, done with cost no object and taken to the extreme. Phase noise reduction was a major design goal. I got given one of the H2900 prototypes in the 1980s. The whole cabinet had been milled out of one slab of aluminium. Marconi trumpeted their receivers in the article and kept their competitors' products anonymous. However, it was dead easy to be sure which some of them were, others left a bit of doubt. Some of the figures fell rather short of the competitors' claimed specs. The competitors' lawyers pounced! Marconi wrote to all recipients of their journal to return all copies.... please!... There was no mention of why. I assume everyone else made damned sure they had a photocopy first new copies were sent out without the contentious material. A spectacular home-goal by the competitors, they could not have made the data more prominent. Decades before Barbera Streisand gave her name to the effect by fighting to get her house masked out on Google Earth. Within Marconi the H2900 was nicknamed Sosin's Folly. It was too expensive for all but a tiny few of their customers. A commercial flop and very rare now. Thumbwheel switch tuning only so no use for amateur interests.

Racal needed a successor to their RA17/RA117. The transistorised RA217/RA1217 was pretty awful. It didn't cut the mustard and they knew it. They licenced the mosfet ring mixer by P R Rafuse (of MIT) and allied it with a decent synthesiser and good filters and brought out the RA1772. A milestone receiver if there ever was one. I suspect those Australian NRD515s may have been the back up for a bank of RA1772s. The RA1772 was not up to the H2900, but at least it wasn't unaffordable (even by government standards).

HP had been involved in low phase noise signal generators and was developing synthesised replacements for the 8640B. Less prominent, there were needs fo very low noise synths to do some particularly demanding measurements on FDM telecomms systems. I got involved in this in the seventies and designed a 5-loop synth for a huge instrument that sank without trace! It was simply too late to a market shifting fast to PCM. But what was learned went into many other things. It's described in the April 1982 HP journal if you want to compare the block diagram of the synth with the NRD515. And yes, there is an MC4044 phase detector in one of the loops, the others use low noise diode sampling bridges and very accurate pre-tuning to get lock.

It was rather good fun being in the thick of it when there were major things happening in receiver design. Frantic at times, but fun.

David

[dave walsh]

I've enjoyed reading this thread for a variety of reasons [thanks Radio 1950] despite being somewhat out of my depth [to say the least] with the theory aspects. Although it's been mentioned I don't recall the 515 being discussed by a Forum member who actually owns one before and it's been helpful to learn about some of the ageing effects as well having confirmation that it was quite a historic and advanced technical break through in the eighties. I recall that the front page advert in Short Wave Magazine WAS this set for quite a while although the price would perhaps have been well out of reach for many people at the time [certainly me] and maybe now? As it happens I have an example of this receiver, matching transmitter, orginal Paperwork, Instruction Manual, Key Pad and even some original boxes I think there may be a speaker unit but can't recall [ironically as you will see].

Here's the story. I was asked to help a gentleman struck down by Altzhiemers Disease round about 1994, whose radio room he still had running without much comprehension or control. I could see he wasn't well as, sadly, he greeted me as an old friend! Once we got everything safely switched off he more or less forgot about it. I did know this chap in a way because his tower and enormous Yagi Aerial couldn't be missed and I often wondered about it while at school as I went past on the bus! I brought people in to help me assist his wife [he died a few years later, she lived until last December]. There was a lot to do. I stored the 515 equipment for three years but eventually I was told to just keep it, along with other radio related items when certain legal matters had been settled. I have his International Awards, Trophies and QSL Cards, Log Books etc that, I fear, would have been skipped otherwise

I used the Receiver now and again through to 1996 but felt a bit awkward, as when I once had a very expensive guitar but little ability to play it. Basically it's been pretty much untouched since then but that might not be such a good thing. Any comments on this aspect will be very welcome!!
Lots of things happened over the next twenty years or so and the situation continues but this thread has prompted me to respond simply because it is rare to see a 515 discussion on here as I said. The only other time I've thought about doing something with this kit was when a new member posted a few years back asking for "high end receivers". He was a bit insistent so I proceeded with caution. Then the Mods gently advised me that I could still make contact privately but he wouldn't be on the Forum anymore for a good reason

I'm aware that these sets are now rare, still expensive and highly regarded by many but not all. I could go down the World Wide Auction sale route but because of the issues I raised and the length of time it's been stored I anticipate complications with that. My ideal purchaser would be someone with patience who could view and test here in E Sussex and would want to preserve and use the equipment as an enthusiast. I'm aware that the basis of a Restoration Site is often spending as little as possible but if an established Forum Member wanted to get in touch I would be happy to discuss things. I'm not going to put it in the For Sale section because [a] It would be very difficult to state a price and keep within the rules. [b] I don't want "new members" suddenly appearing and creating problems for the management. I am hopeful that mentioning it here keeps me below the Radar. I wasn't sure about posting in this thread at all or the perhaps unusual request that I make. If I have breached the rules/ethos in anyway, perhaps this last paragraph could just be deleted. Info about reviving the units/ possible problems would still be very much appreciated although I shan't be rushing to do anything with it myself. Basically I'm giving the Forum a first preference [just in case] while seeking advice and "testing the water."

Dave W

[Damien VK3RX]

NRD515s would have made an effective emergency backup to these and allow the system to be monitored for about a tenth the cost of MOPS-compliant receivers.

A commonwealth government organisation I worked for used Eddystone 1830/1 units (with crystals) for backup till the late 70's, then the JRC NRD-515 and NDH-518 memory unit.

The JRC units were certainly easy to operate for non-technical users; select a memory or just dial in the desired frequency.

For nostalgia I had both at one time. Kept the Eddy and moved on the JRC.

Regretted the latter ever since It had Sherwood filters and main board mods done when I bought it.

[dave walsh]

Oh yes thanks Damien-I think there is the memory unit [another sad irony] as well, now you mention it, to go with the keypad. The main units are certainly together but the sundries may need locating.

Dave W

[Radio Wrangler]

It's well worth rounding up all the sundries. They make quite a difference to useablity.

Sherwood Engineering in the US did super duper improved filters for a number of well-regarded receivers, especially Drakes. If you have a look at the ARRL's list of all time pecking order of dynamic range tests, you'll find several Sherwood-equipped receivers figure quite well.

David