How to hear NASA satellites...

[Al (astral highway)]

I’ve just finished building and testing a June 1962 circuit from Popular Electronics. It’s a converter for listening to satellites – in fact the featured article of this copy (June) was ‘How to Hear NASA Satellites.’ I was born a couple of years after the Bay of Pigs episode and have always been interested in the cold war, electronic surveillance and the superpowers’ efforts to harness technology.

I found fascinating the idea of tuning in to milliwatt transmissions from 23 thousand miles into space, in the hope of picking up a signal from one of the earliest satellites, TIROS 10 at 136.235 MHz.

This is my choice, as the satellite went up 3 years after the circuit was published. The original article describes Explorer XII, Telstar I, s-51, Injun SR-3, OSO and TIROS IV, all sub-137 Mhz.
Curiously, although it references the Iron Curtain, it doesn’t list Soviet satellite frequencies of the time.

The original design was by Tom Lamb, call sign K8ERV.

I have made two off-the-cuff recordings on a mobile, and am excited by these first results. [These are currently real-player files - please PM me if you know how to convert to .MP3 so that I can post the audio files thx.]

What it does:
The completed set plugs into any comms receiver and allows you to tune it on the 15 metre band as if it were an (approx) 2 metre receiver of great sensitivity.

The set-up:
It’s appealingly based on a now little heard-of device, the nuvistor, which is basically a thimble-sized triode. That’s the RF amplifier. The mixer is a triode-configured 6AK5 valve and the local oscillator is a crystal-controlled 6AK.

The IF is available at the BNC socket of the set which is impedance matched to 50R for feeding to a comms receiver with standard RGB coax. The LO is tuned to the 3rd harmonic of the 38.66666 Mhz crystal, 116 Mhz.
You have to get these custom-made (mine was from Canada) but I only paid £10 for this critical component.

The valves are very low power devices and the mixer and LO run very cool. The nuvistor has a metal can and because of its tiny size, it runs hot just dealing with the heater.

The power supply is half-wave rectified, unregulated, and goes through a simple pi network. Under load, it delivers 130V HT+ , which is about as safe as it gets with valve equipment.

Mine is housed in a casing from a piece of WWII military equipment, using transformers I had to hand. I’ve added an NTC thermistor to the heater supply. I may add basic regulation later on.
The set-up dwarfs the little converter, but there’s a lot of air in that box.

The tricky bits:
A single loop of wire around one of the local oscillator’s tuning caps feeds a tiny signal to the mixer. This ingenious trick is to avoid loading the LO.

The coupling is critical. I had to install a physically bulkier cap than originally specified to get coupling from the loop in line with the text's test readings. You can see this in one of the pictures - a white insulated wire wrapped round the porcelain body of an ex-military equipment trimmer cap.

There are quite a few coils to wind. Thanks to Skywave (Al) for helping me work out how to wind the impedance-matching xformer (four windings on two formers with twisted pair transmission line).

If you do as I did and build it on a double sided printed circuit board, that goes a long way to minimising stray inductance as you can ground a component practically anywhere you want to. (You can’t do this with tag-strips, clearly.)

Results:
Last night, I tuned all the way from 20-27Mhz on my comms receiver, which of course is 136-143 Mhz in real money. You will get lots of strong carrier waves as you tune these frequencies. You also get unintelligible FM periodically but a stub will fix this.

Eventually, I got something very interesting. The first hit was at 141.000 Mhz exactly. There’s nothing on my list to match that, but it's the first of the recordings below.

The second hit was at 145.971 Mhz which could be COSMOS 2398, used for navigation and comms.

Incidentally, I suspect that the anode circuit which tunes the local oscillator, isn’t sharp enough at the moment, and that’s partly why I’m getting a ‘broadband’ reception. I’ll find out when I run tests later.

Next steps
It’s a bonus that the receiver is more broadband than I expected – it was designed for 136-137 Mhz, but here I am tuning up to 145 Mhz. On the other hand, this of course probably means that the set is less sensitive than it could be at the original target frequency.

I intend to tune to the very oldest satellites, including TIROS, and so I could do with ensuring that the set is as sensitive as it could be at 136-137 Mhz. Higher-frequency stations are coming in more strongly at the moment, but bear in mind that I haven’t properly calibrated the set. I’m getting a second hand RACAL siggy soon and will use that to calibrate the converter properly.
I could also do with a more selective antenna. I’m using the TV aerial.

The set runs of a half-wave rectified power supply and uses 130V under load and has a huge grounded surface so I’m not too worried about housing it in a hurry, but I could finish it nicely with a case made from printed circuit board.

Any comments most welcome! I can post a scan of the circuit this evening if anyone's interested.

I'm a happy punter as this is the first VHF+ valve circuit I have ever consructed.

[dave walsh]

Al it's interesting that you built a device from the same era instead of just a modern scanner or similar receiver. Are you are using the UHF tv aerial? That's quite a mismatch so something designed for 136 megs could be really interesting. Ive no experience of Nuvistors myself but I didn't think they were that obscure. They are referred to in 60's editions of the RSGB Handbook. I've got a Nems Clarke RX with a similar sort of device on the front end. It's hard to get info on these sets although a web site is slowly building up. I couldn't understand this at first until I realised that they were used in the NASA program. Dave

[Al (astral highway)]

Hi Dave. Exactly, I know I could have gone out and got a scanner, but I thought 'Where's the fun in that?' The attraction was that here was a circuit that was put together in the middle of the Cold War and in a way, celebrated the might of NASA. It's a sensitive wee beastie, too. My correction:when I say that nuvistors are 'obscure', that's a relative term. I'm judging by the number of mentions they get in practical wireless, practical TV and practical electronics of the period -- very few, from what I can see. Of course, the cognoscenti know about them, but isn't it fair to say they were virtually eclipsed by transistors, so RCA probably never recouped their research costs?

How sensitive is the Nems Clarke RX?

Here is the circuit, by the way.

[Station X]

Where did you get the coil formers from Al?

[Al (astral highway)]

Hi Graham. They came from a supplier in the US for a few dollars. As an inveterate collector of eye-catching inductors, I got them a while back with no particular use in mind. Five of them were mounted on a single punched and grommeted stainless steel strip, if that gives any clues as to the origins of the equipment.

So they were just sitting there in a drawer, waiting to be used, and when I saw this circuit, I thought: ahah, now's your moment.

[brunel]

To change your real media to another audio format try "Super"

http://www.erightsoft.com/home.html

Brunel

[Al (astral highway)]

Thanks Brunel. I'll try that and post the results late this evening.

[MichaelR]

good little project AL

Mike

[Al (astral highway)]

Thanks Mike.

[HMV 1120]

Any chance of picking up 'Prospero', Britians only self-launched satelight? I gather it is still active between 137-138MHZ, although only it's timer signal can be recieved.
Great set up, satelight reception is something I've always wanted to try. Can't justify the money on a scanner though (this is a shack on a budget!), so perhaps a converter would be sensible way to go.

[jjl]

Originally Posted by astral highway

My correction:when I say that nuvistors are 'obscure', that's a relative term. I'm judging by the number of mentions they get in practical wireless, practical TV and practical electronics of the period -- very few, from what I can see. Of course, the cognoscenti know about them, but isn't it fair to say they were virtually eclipsed by transistors, so RCA probably never recouped their research costs?

Al

I believe that nuvistors were quite widely used in professional and test equipment up to the late '60s / early '70s. My 1968 vintage Tek 454 'scope uses them in the amplifier input stages and timebase.

John

[ppppenguin]

Nuvistors were also used in TV camera head amplifiers. The Philips PC60, an early Plumbicon camera dating from around 1966, certainly used them.

Along with compactrons they were very much the last gasp of valve technology for low and medium power applications. For the camera application I mentioned FETs soon outclassed nuvistors.

[dave walsh]

I've just recalled that in one of the Coast BBC TV programs they went to the research site on the Isle of Wight where the British Space Program research was done. They used a portable rx and hand held dipole lash up
pointed at the sky, to look at the 136 meg band tand see if a particular satellite was still going round-and it was! Not sure if it was a Nasa one though. Probaly Prospero that HMV mentioned. Dave

[Skywave]

Hi Astral
From your OP:

<< Incidentally, I suspect that the anode circuit which tunes the local oscillator, isn’t sharp enough at the moment, and that’s partly why I’m getting a ‘broadband’ reception. I’ll find out when I run tests later.

It’s a bonus that the receiver is more broadband than I expected – it was designed for 136-137 Mhz, but here I am tuning up to 145 Mhz. On the other hand, this of course probably means that the set is less sensitive than it could be at the original target frequency.

. . so I could do with ensuring that the set is as sensitive as it could be at 136-137 Mhz. Higher-frequency stations are coming in more strongly at the moment. >>

Ok - the cct. works - it's pretty basic, but it works

A few observations.

I see that there is only one tuned L/C cct. in the whole signal chain - and that is at the IF. For a converter aimed at covering 136 - 137 MHz (1 MHz bandwidth), I would have expected to see a tuned input or tuned output at the RF amp. (not both - it'll oscillate like crazy. Yes - I can see that the RF amp. - as is - has neutralisation). A tuned RF amp. narrows the bandwidth, reduces image response and improves the S/N ratio.

Further, since the mixer is a pentode, I would have preferred to see the LO injection other that by adding it to the signal grid at these frequencies.

Finally, I see that the aerial input winding is configured for a balanced aerial. When you get around to using a more effective aerial, you might like to consider using a balun - if the aerial will use coax (most likely) or re-config. this input cct. for unbalanced (i.e. coax) feed.

The signals your chasing are pretty weak anyway - so anything which improves the S/N & selectivity is welcome.

Having said all that, though, overall I'm quite impressed with what you have achieved - well done!

Al / Skywave.

[Al (astral highway)]

Thanks for the support, Al.

I appreciate your comments on how the original circuit might be improved for greater selectivity. Having said that, I don't want 'scope creep' with this project or it will never end..! So I think I'll leave this one broadly as it is in the original cct and reflect on your comments and perhaps integrate these sophistications in a future prototype.

But I'm particularly taking on board your comment about the aerial and balun -- I think my priority should be to get hold of a 41 inch dipole that the text refers to.

The signals your chasing are pretty weak anyway - so anything which improves the S/N & selectivity is welcome.

Very true!

[Al (astral highway)]

Any chance of picking up 'Prospero', Britians only self-launched satelight? I gather it is still active between 137-138MHZ...

I didn't even know about Prospero, to be honest. Shame on me! I'll have a go hunting it down when I'm tuning this slightly lower frequency range than I can successfully as the set stands.
I'll make a recording if I get anything.

[Skywave]

Originally Posted by astral highway

. . . So I think I'll leave this one broadly as it is in the original cct. . . .

Very wise; if it ain't broke . . . don't fix it!

I just felt the urge to make a few passing comments for the benefit of the 'wider audience'

Incidentally, since that last post of mine, I've been looking at some ccts. of Nuvistors (6CW4) for (a) HF band pre-amps. for comms. receivers; (b) RF amps. for converters for the 70 MHz and 145 MHz AmRad bands. I know that somewhere in deep storage I have a couple of brand new 6CW4 that I bought way back in the '60's to have a shot at (b) . . . but like many things, the project got shelved for 'another day' . . .

Al / Skywave.

[Al (astral highway)]

Originally Posted by Skywave

Very wise; if it ain't broke . . . don't fix it!

Very wise.

Interesting to note the doppler effect when I 'tuned in' to a satellite in the mid-143 Mhz this evening. I had to keep retuning and after four minutes, lost all but the weakening carrier wave.

[chipp1968]

Im amazed there are satellites even surviving , let alone still sending signals from space dating from the 1960s
fascinating

[Al (astral highway)]

I've now converted the recordings to .mp3 format but these still won't upload. Mods: is there a way of doing this, please?