Extending Langstone to include 10GHz

Forum for discussion about the Langstone Microwave Transceiver that shares some features with the Portsdown. Wiki: https://wiki.microwavers.org.uk/Langstone_Project
g4eml
Posts: 673
Joined: Thu Apr 26, 2018 9:36 am

Re: Extending Langstone to include 10GHz

Post by g4eml » Thu Oct 01, 2020 12:53 pm

Hi Barry,
I am happy that it is working for you.
Your picture actually shows the horn on the Tx port of the Pluto if you really were receiving like that then you may find the sensitivity is better with it on the Rx port. The Pluto is unscreened so it does receive even without an antenna.

Regarding the TCXO, The LO is on the low side of the signal so if it is being received on a higher frequency than it should be it would indicate that the LO is low in frequency.

You got me thinking about the error correction. I think the calculation is roughly

(10368.150/10368.2488) * 40 =39.99961883630725

So using a Pluto TCXO correction value of 39999619 should get you close.

I say roughly because the LO actually moves in steps of 100Khz and then the SDR works as if it was a tunable IF from 50 - 150 kHz. So the error is actually in the LO frequency. But I would think it is close.

73
Colin

G8AGN
Posts: 34
Joined: Mon Mar 05, 2018 1:41 pm

Re: Extending Langstone to include 10GHz

Post by G8AGN » Thu Oct 01, 2020 3:59 pm

Colin

that's quite remarkable. I must have forgotten to change the horn over to Rx when I had finished playing with Tx on the lower bands!

Many thanks for the TCXO correction calculation. I will try it out later today.

73 Barry

G8AGN
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Joined: Mon Mar 05, 2018 1:41 pm

Re: Extending Langstone to include 10GHz

Post by G8AGN » Thu Oct 01, 2020 4:57 pm

Colin

I should clarify my last e-mail. I wasn't using the horn to transmit on 3.4 and 5.7GHz but one of Sam's 2-11GHz LP antennas,

73 Barry

G8AGN
Posts: 34
Joined: Mon Mar 05, 2018 1:41 pm

Re: Extending Langstone to include 10GHz

Post by G8AGN » Sat Oct 03, 2020 9:31 am

Colin

I ended up measuring the frequency of the TCXO itself using a scope probe just touching pin 3 on the TCXO and using a counter with 10MHz external reference from a Chinese GPSDO "standard". I then transferred this measured frequency to the Pluto using Putty and the commands
fw_setenv xo_correction 39999525 and then reboot. The new TCXO value then shows up in the config.txt file.

My measured TCXO frequency is still not quite correct but much closer and on 10GHz my error is now around 20kHz, I have a better TCXO on order so will fit that when it arrives and repeat the procedure.

The Pluto is very sensitive on 10GHz even without an antenna so due to pickup through the plastic case as you suggested earlier.
I like the ease of tuning with the mouse.

What is the amplitude range of the spectrum display?

73 Barry, G8AGN
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g4eml
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Re: Extending Langstone to include 10GHz

Post by g4eml » Sat Oct 03, 2020 12:09 pm

Hi Barry,

With an upgraded TCXO my system seems to stay well within 1KHz at 10GHz.

The vertical range of the spectrum display is 50dB and is logarithmic as you would expect. The range is not adjustable but the base level can be adjusted for each band to compensate for preamp gain etc.

Sensitivity on most bands is extremely good even without external preamps. 10GHz is reasonable and perfectly adequate for local testing. When I compared it to my Kuhne transverter it was about 30dB down. Adding an external 30dB preamp followed by a pipe cap filter brought it up to about the same sensitivity.

I haven’t tried using harmonic mixing for any other bands but I guess it might be usable at 8GHz for spacecraft reception. 24GHz might be pushing it a bit but I may give it a try.

Transmit power on 10GHz is around -30dBm, again plenty for local testing. The Tx attenuator setting also seems to remain reasonably well calibrated. So it can be used to provide a very low level test signal for checking other receivers.

73
Colin.

g4eml
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Joined: Thu Apr 26, 2018 9:36 am

Re: Extending Langstone to include 10GHz (and 24GHz!)

Post by g4eml » Sat Oct 03, 2020 2:19 pm

I have just tested my Langstone set for 24GHz and can confirm that it does work!
Both transmit and receive working OK to my transverter with open waveguide on the other side of the shack with no antennas on the Pluto.
I am sure the transmit power and receive sensitivity will be quite low compared to a ‘proper’ rig but it is certainly usable as a test source and monitor receiver. Also I suspect the main signal route may be directly into and out of the chip rather than through the antenna connectors. The losses through the internal transformers must be quite high.

Unfortunately I don’t have any 24GHz test gear to properly check the performance.

Just set the Tx and Rx offsets to zero , the Tx and Rx harmonic to 5 and the frequency to 24048.100

It will of course still also be radiating and receiving at 4.8 GHz so, like 10GHz, external filtering would be needed.

Colin G4EML

G8AGN
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Joined: Mon Mar 05, 2018 1:41 pm

Re: Extending Langstone to include 10GHz

Post by G8AGN » Sat Oct 03, 2020 3:20 pm

Colin

I have mine receiving on 24GHz using a paper clip as the antenna. The signal is not very stable due to the 25ppm TCXO but still very impressive. I'm using the 7th harmonic of 3435.46 MHz as the Tx signal.

73 Barry, G8AGN
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G8AGN
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Re: Extending Langstone to include 10GHz

Post by G8AGN » Sat Oct 03, 2020 3:33 pm

Colin

I'm not sure I believe this but have no way of checking

11th harmonic of 4280.75

73 Barry G8AGN
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g0mjw
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Re: Extending Langstone to include 10GHz

Post by g0mjw » Sat Oct 03, 2020 3:40 pm

I doubt that's a real reception. Interesting if it is though.

Mike

G8AGN
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Joined: Mon Mar 05, 2018 1:41 pm

Re: Extending Langstone to include 10GHz

Post by G8AGN » Sat Oct 03, 2020 3:47 pm

Colin

False alarm as I hadn't set the offsets to 0 and x5 sorry.

I cannot see my marker on 24 or 47 after all -- too weak.

73 Barry

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