Langstone V2... Now with Lime Mini Support

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

Re: Langstone V2... Now with Lime Mini Support

Post by g4eml » Tue Mar 15, 2022 1:53 pm

Hi Dave,

I haven’t done much testing with the Lime, I have just used the default GNU Radio modules and settings.

It may be that forcing a recalibration would improve the balance but it is not something that seems to be supported by the GNURadio module. If I get the time I may investigate some more.

I have got the general impression that the Pluto seems to have a better RF performance than the Lime. The Lime’s USB connection is much more reliable though.


Colin.

G4FRE
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Re: Langstone V2... Now with Lime Mini Support

Post by G4FRE » Wed Mar 16, 2022 12:01 pm

After doing some receive comparisons on the GB3SEV 2m beacon last night I agree that the Pluto has the better RF performance. Even with an external BPF (to avoid overload) I had to drop the Lime gain from the default 73 (there is no "auto" )to 20 to even detect the beacon. Using the Pluto with gain of 73 it was a good signal

Now going ahead and finishing the Portsdown4XV with a pluto. I will just have to live without the limes DATV spectrum display!

Dave
G4FRE

radiogareth
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Re: Langstone V2... Now with Lime Mini Support

Post by radiogareth » Wed Mar 16, 2022 2:36 pm

If you are stuck you can use a RTL dongle on an old Android phone with SDRTouch. Does what you need in terms of 'seeing the RF'...
Gareth

G8GKQ
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Re: Langstone V2... Now with Lime Mini Support

Post by G8GKQ » Sat Mar 19, 2022 10:20 am

I looked at the poor key-up/key down performance of the LimeSDR Mini with Langstone V2 last night.

Reducing the TX gain to 69 or below increases the on/off ratio to 42 dB. It also significantly improves the carrier suppression in USB. More investigation to follow.

Dave

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

Re: Langstone V2... Now with Lime Mini Support

Post by g4eml » Sat Mar 19, 2022 11:28 am

My Langstone test rig is in bits at the moment while I try to repair a blown up Pluto! (There is a short on the power supply).

Once it is all back together I will have a look at the CW performance. At the moment just the IQ inputs are keyed but I could probably also key the Tx Gain between its set value and zero. That might give a larger ratio. There doesn’t seem to be any way of turning off the Tx local oscillator completely.

SSB carrier suppression would be more difficult to fix but is not really that important. It doesn’t really affect the readability.

Colin G4EML

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

Re: Langstone V2... Now with Lime Mini Support

Post by g4eml » Sun Mar 20, 2022 10:24 pm

I am getting similar results to you Dave. Reducing the TX gain to 66 gives a big improvement in residual carrier level. It looks like the Lime doesn’t perform so well at maximum output. It may be necessary to limit the maximum gain setting, but that will obviously reduce the available output level.

Colin.

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

Re: Langstone V2... Now with Lime Mini Support

Post by g4eml » Mon Mar 21, 2022 9:53 pm

After a lot of experimenting today the best carrier suppression I could achieve with the Lime Mini was 50dB. To do this, as Dave found, I had to reduce the Tx Gain to 66dB. This reduces the maximum output power to about +6dBm. Running the Lime calibration did not improve on this.

I tried adding a manual adjustment for the I and Q offsets but this only resulted in an improvement of a couple of dB, so I decided it was not really worth the hassle of including it.

I also made several other changes to improve the Tx performance on CW, SSB and AM. The previous settings were overdriving the Lime under some conditions.

The updated software has been uploaded to Github so you should be able to do an update.

Overall the Pluto still seems to perform better than the Lime. The carrier suppression is closer to 70dB with the Pluto. Its a pity its USB connection is so unreliable.

Colin G4EML

G4FRE
Posts: 197
Joined: Fri May 26, 2017 6:57 am

Re: Langstone V2... Now with Lime Mini Support

Post by G4FRE » Wed Mar 23, 2022 3:17 pm

I did try reducing the TX gain on Sunday and found a sweet spot with 40dB of carrier suppression but the output was only -16dBm so an external amplifier would have been needed to restore the level

I updated the Langstone software last night and have noticed the suppression is around 50dB now at 0dBm output. Much improved and good enough for casual DATV expeditions!

I did use my original portsdown with Lime to work Gareth on Monday. It was worth it for the Band viewer and being able to generate a carrier in the portsdown mode

Dave
G4FRE

g4eml
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Re: Langstone V2... Now with Lime Mini Support

Post by g4eml » Wed Mar 23, 2022 3:25 pm

Hi Dave,

I must admit I don’t really know exactly what’s going on. The Lime seems to behave unpredictably. I think at least some of it might be down to overheating. I had one situation where the carrier suppression dropped to 20dB and I could not improve it. After leaving it overnight it came back to 50dB with me doing nothing!

Overall I will still continue to use it, mainly because it’s more compatible with the other Portsdown features.

Colin.

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