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Old 29th Nov 2017, 4:32 pm   #1
Al (astral highway)
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Default Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

I was intrigued to see this data capture of a transmission from Voyager, picked up at 140 Astronomical Units (Earth-Sun distances=12+Billion miles) from earth the other day. Attached photo shows all the details.

Astonishingly, this is from Voyager's on board transmitter at just 22W, at a transmit frequency of 8.4GHz. I can only imagine the size of the array needed.

Voyager's transmitter will be detectable from earth until 2025, which is just astonishing. The next significant encounter she will have , in very deep interstellar space, will be in 40,000 years time.

All of this reminded me of a VHF+ converter I built shortly after I joined the forum, almost ten years ago. I'm linking to it again as most of the people who saw it at the time are no longer active on the forum and conversely, most of the people who are active now were not active then...

It used a Nuvistor in the front end and I was initially trying to pick up transmissions from NASA's early 1960s satellites, including TIROS. The design is from a 1962 Practical Electronics article. The converter enabled me to listen to transmissions at above 140+ MHz using a pretty standard comms receiver on the 15m band, as if it were a 2 metre receiver of great sensitivity and selectivity.

This was a far-fetched idea indeed, but I thought I might pick up even a carrier wave. The project was great fun, however, and I managed to listen to many contemporary satellite comms instead, using a simple dipole aerial only about a metre long, and then even more with a proper home-made loop aerial.

I recorded some of the transmissions and you can clearly hear the Doppler effect as the satellites pass over earth.

I hope you enjoy the circuit and also the comparison with the current attempts by NASA to keep track of Voyager, which are just astonishing, to me, anyway.
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Last edited by Al (astral highway); 29th Nov 2017 at 4:44 pm. Reason: typo
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Old 30th Nov 2017, 9:47 am   #2
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Hello, the scan looks small so I can dig out the original article if anyone is interested, including the narrative and circuit diagram from 1962’s Practical Electronics (before I was born).
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Old 30th Nov 2017, 10:10 am   #3
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Thanks - I will give it a look
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Old 30th Nov 2017, 10:23 am   #4
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

I looked back at your original, and it's actually Popular Electronics, June 1962. It is available on the American Radio History site (I have just downloaded).
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Old 30th Nov 2017, 11:01 am   #5
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Wow, that takes us back in time! There is a fascination in looking for old satellites. The old LES-1 is still alive (just) after 52 years in orbit and its signal can be heard when the satellite is in sunlight and within view. Its batteries failed years ago. It's on 237 MHz (dopplering LF) and you can find a prediction chart for the UK here: http://www.n2yo.com/passes/?s=1002
I receive it on an SDRPlay RSP2 SDR with a DAB dipole outside. It's pretty weak!
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Old 30th Nov 2017, 1:11 pm   #6
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Quote:
Originally Posted by ionburn View Post
it's actually Popular Electronics, June 1962. It is available on the American Radio History site (I have just downloaded).
...

Oops,you're quite right. And here are scans of the original.


Quote:
Originally Posted by Andrew2 View Post
Wow, that takes us back in time! There is a fascination in looking for old satellites. The old LES-1 is still alive (just) after 52 years in orbit and its signal can be heard when the satellite is in sunlight and within view !
Yes, it's pretty fascinating stuff. I know thesedays anyone can buy a scanner and sweep VHF+ to UHF, but there's something wonderful about using the Nuvistor in the front end of this circuit, and the set will work nicely off a 90V battery. It's pretty neat.

I was reminded of the RCA Nuvistor by Argus25's (Hugo's) mention of the Fetron yesterday. It sounds similarly sci-fi, at least to me!
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Old 30th Nov 2017, 1:55 pm   #7
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Back in 2013, a radio telescope detected the exact position of Voyager when it was about 11 billion miles away. Here is an article about it. When you read further down, the telescope 'easily detected the spacecraft in less than a second....'! Not bad from a 22 watt transmitter....
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Old 30th Nov 2017, 2:13 pm   #8
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

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Back in 2013, a radio telescope detected the exact position of Voyager when it was about 11 billion miles away.

Yep, it's pretty phenomenal!

I was delighted to pick up satellites much closer to home, orbiting earth. It's incredible when you hear the Doppler effect.
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Old 30th Nov 2017, 2:19 pm   #9
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Nice! That circuit is very much one of the standard VHF/UHF converter ones from the early-1960s, very similar ones being built by countles radio-amateurs so they could receive 2-Metre amateur transmissions on their HF-bands communications receivers.

[5th overtone crystal on 116MHz puts the 144-146MHz VHF amateur-band on to 28-30MHz as a tunable IF]

The 6AK5 valves as used for the mixer and oscillator are direct descendants of the 1930s "Acorn" valves that were used in a great deal of WWII-era Radar gear. Triode-connecting the 6AK5 as a mixer in that circuit is good - it gives a lower level of self-generated noise than the more-usual pentode-mixer circuit - important when you're searching for signals that are barely above the background cosmic-noise level anyway!

Nice to see the ex-Army variable capacitor [the one with the ZA label..] in your construction!
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Old 30th Nov 2017, 2:59 pm   #10
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

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Originally Posted by G6Tanuki View Post

The 6AK5 valves as used for the mixer and oscillator are direct descendants of the 1930s "Acorn" valves that were used in a great deal of WWII-era Radar gear. Triode-connecting the 6AK5 as a mixer in that circuit is good - it gives a lower level of self-generated noise than the more-usual pentode-mixer circuit - important when you're searching for signals that are barely above the background cosmic-noise level anyway!
That’s interesting, thanks: I mean the evolution from their Acorn ancestors! I have some Acorn types in my collection. I found the converter very noise-free, as you suggest, and sensitive. I think signals were of the order of 5uA

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Nice to see the ex-Army variable capacitor [the one with the ZA label..] in your construction!
Well-spotted! I love using ex-Mil components when I can-just for the sheer quality as well as their aesthetics.
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Old 30th Nov 2017, 3:47 pm   #11
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

The immediate descendants of the original 95x-series of Acorns were the 9001 to 9003, which appeared early in WWII.

http://www.r-type.org/exhib/aab0161.htm
http://www.r-type.org/exhib/aaa0254.htm
http://www.r-type.org/exhib/aaa0253.htm

partly to fix the issues that Acorns had wth the sealing of the 'legs' to the glass.

The 6AK5 came on the scene as an improvement over the original pentode acorns: RCA/AT&T/Bell Labs promoted it as a wideband VHF/low-UHF amplifier - it was used in some of the first 'sending thousands of phone calls down a single coax cable' multiplexing/subcarrier work because of its ability to deliver consistent low-noise gain across a wide bandwidth at VHF.

Then, of course came the likes of your 6CW4 Nuvistor, which must be regarded as the last gasp of the vacuum-tube industry in the face of overwhelming competition from transistors.
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Old 30th Nov 2017, 6:21 pm   #12
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

I've still got the 2m converter I built around about 1968. Published in PW, it had an ECC88 (I think I had an E88CC with gold pins!) in cascode at the front and a pair of ECC81's doing the other stuff. There were some 46.7 MHz crystals selling for pennies at the time, so the IF was roughly 4-6MHz. Later on I added a pre-amp with a pair of 6CW4's in cascode. I don't think the overall S/N ratio would ever have won any prizes but it got me going on 2m.

The (surviving) people who built the Voyager spacecraft have good reason to be immensely proud of them . I saw the guy who was the original Project Manager interviewed on TV a while ago, and he talked about how his children and then his grandchildren had grown up and followed the mission.

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Old 30th Nov 2017, 6:57 pm   #13
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

For reference, here's a grabbed-from-a-1970s-RSGB-publication table of noise-figures of RF amplifiers and mixers.

[In terms of weak-signal performance, the valves with the lower numbers are the ones to choose]

Alas it doesn't show the 6CW4 Nuvistor's NF as a RF amplifier, but it does show the noise-figure for the 6AK5 *as a pentode*. Uusing it as a triode would give a noise-figure more like those listed for the 6J6 12AT7 or 6U8(triode) or the other triodes shown.

"Multigrid" mixers are truly gruesome in terms of internally-generated noise - look at the number for the 6K8!! Even the ECH81 is enough to trigger anxiety....

All in all, choosing a triode-connected 6AK5 as the mixer for your circuit was really rather cunning - its noise-contribution to the signal would have been really small so less likely to mask the weak signals you were trying to receive.

[The only downside of triode mixers is that they don't provide much isolation against local-oscillator feedthrough, which can become a serious issue when the intended received-frequency and the local-oscillator frequency start to converge]
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Old 1st Dec 2017, 2:43 am   #14
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

The 6J6 comes up very well in the specs on that table. These were popular in RCA TV tuners immediately post war, used as a mixer oscillator, rather than as a cascode amplifier as I recall.
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Old 1st Dec 2017, 8:25 am   #15
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

The 7360 makes a good showing as well.

Its finest hour was probably as the mixer in G3PDM's very high performance HF receiver.

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Old 1st Dec 2017, 10:54 am   #16
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Hi

I'd like to have a go at constructing the converter that astral highway built but the nuvistors seem slightly expensive. Is there a good proven FET design converter for 136/137MHz that anyone can recommend?

Regards
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Old 1st Dec 2017, 2:40 pm   #17
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Symon, it would be a shame if you didn't have a go at building the original design. I can let you have one, if it means you can go ahead with the design.

I'll PM you.
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Old 1st Dec 2017, 4:10 pm   #18
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Hi Al.

That's a very kind offer thanks.
PM sent.

Regards
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Old 1st Dec 2017, 5:40 pm   #19
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Great, Symon, sent! I hope more people are inspired to build the converter. It's really neat and with a bit of forethought, it could be built with a tiny footprint.
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Old 1st Dec 2017, 5:57 pm   #20
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Default Re: Home brew converter to listen to Satellites, plus capture of Voyager TX by NASA

Quote:
Originally Posted by Philips210 View Post
I'd like to have a go at constructing the converter that astral highway built but the nuvistors seem slightly expensive. Is there a good proven FET design converter for 136/137MHz that anyone can recommend?
Symon, you'll need a socket for the Nuvistor and, they're around but not common. The last ones I saw online (some time ago) were being sold in packs of 4 for £22.

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