#LimeSDR Transmit Anomaly #limesdr


jose maria trueba
 

Hi Mike, Sigi and Joe,

Thanks for the 50ms hint, Mike. I will try it.

Sigi,
Your skyworks 20dB gain MMIC does look great. Mine is only 12dB gain, which means that I need to use 8dB more power from LimeMini than if I would replace my MMIC with the one that you've got.
I have three amplifiers after LimeMini, 12+21+17=50dB gain in all, so I need -10dBm from Lime to get 10w output power and -7dBm from LimeMini for my regular PEP which is around 20w with final linear amplifier working at 14VDC (I get around 50w at 26VDC). 

My unmodified Lime Mini does have a strong jitter, but it gets better after several minutes. I have mot seen any otjer Lime Mini carefully. I wonder if other people can see such a strong jitter as mine.A very unacceptable jitter comparing with Sigi's Pluto with TCXO replaced, and Joe's Lime SDR using an external OCXO.
I did check what happened if beacon is unlocked and I saw no differences. I sent another picture with neacon unlocked and we could see the drift but jitter was as bad as with the beacon locked.
I will try an external reference in the future (I already have two SMA connectors ready for this purpose fitted at the rear panel).

I do not see the central spur if Lime power level is set normally, to any output level lower than 10dB below max power, but I can see it if I push TX power to -5dB. I agree with Sigi that is better to set TX offset to 0KHz so we can see easily what happens with the spur. By the way I do not see it exactly at the frequency where an AM carrier would be located but around 900Hz below that point. I had no idea why but it must be that I had my XIT set to +860Hz, that must be the reason why most probably.

I have talked with Sigi several times after our very first and very short QSO, the first day that I went on air through QO-100. He is a very enthusiastic ham and it is always a pleasure to talk with him.
Yesterday Joe and I met for our first time and we had a super.interesting and long QSO until we had to quit to have lunch. I learnt many things including that Israel time is only one hour ahead of central European time. Really it's a pleasure to meet so many nice and very interesting people.
This sat is really something!

73,
jose, ea2jx



jdow
 

That may not be particularly good for CW, AM, PM, FM, and digital modes. For SSB and SSB generated digital modes it's ideal.

{^_^}

On 20200530 08:48:25, MikeC wrote:
I agree about the levels. Anything above about -10dBm output causes distortion so there needs to be and amplifier for whatever you are using.
I also rather agree about the offset frequency, I always set it to 0Hz and then the spur is where your carrier would be in SSB. If the tx cal is done and the output level is not above -10dBm the spur is very low.
Maybe I was lucky with the hanging problem being solved by adding the 50ms tx delay, but it did fix it on the slower pc – I think....
This noise problem is the one that is causing me most concern at the moment particularly if you are running any power.
Mike
Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10


josephlevy
 

Hi max zoom 20 lps
Single tone transmitted
High beacon (look at the part that only a single tone)


Siegfried Jackstien
 

he see wobble also with no beacon lock ... (but then additional drifting)

please please ... do NOT use offset ... if there IS a spur ... you see it in your own if display (next to your passband) and you just do another tx calibrate (and spur should be gone or a lot lower) ... if you use offset ... then you may send the spur without notice (but may disturb on anotherones frequency) ... so best is to set that to 0hz ... and in case you see your own spur do a tx calibrate (do NOT FORGET TO SWITCH OFF AMP!!) ...

jose also measured how clean (or not) the lime is with different levels ... and he also wrote to stay 10 db or more below max power (and use another lna in the chain) ... in that level range gain is cheap :-) ... i use a skyworks65017 for around 20 db gain from 0.1 to 6 gig ... VERY nice broadband amp for a few mw out

first pic is jose

secondand third is my pluto ... first half with beacon lock on and second half beacon lock off

lnb is only tcxo modded and tcxo is INSIDE lnb but we have almost stable temp outside (cloudy and only a tiny bit of wind) so lnb drift is low

spectrum set to x8 resolution and 20 lines/sec on waterfall speed in first and 10 lines/sec on second picture

compare that with what jose sees ... his signal wobbles a lot more even if i do not count the maximum swings (100hz) but only the mean swings up and down (say 30 hz or so) ...

so all lime and maybe also pluto users ... please post a screenshot ... resolution x8 .. 10 to 20 lines wf speed and max zoom ... so we can compare the results (internal and external reference welcome)

joe ... may you also do the same test and post a screenshot??

greetz sigi dg9bfc



Am 30.05.2020 um 15:36 schrieb josephlevy via groups.io:

Hi Jose and Sigi
I can relate my experience with the LimeSdr USB

Do not transmit anything near the max power out.(signal is way distorted  then)
I set it to -20Dbm  (so needed another amplifier in the chain to reach the 2.4 Ghz for the Qo100)
But then it does not get stuck, no central spur (I use 250 khz offset) and see no spur anywhere on the full band of the Qo100)  (peak signal when modulating with a single tone S9+12
and nearly 37-8 S/N).
BTW   Jose I use now the X8 resolution on the waterfall and then you can see very accurately any Jitter in your signal, and mine is very similar to the band edge Beacon. If the 'lock to Beacon' is wobbling (a bit, not complete unlock) the you'll have wobbling on your TX freq.)

De Joe 4X1RV


MikeC
 

I agree about the levels. Anything above about -10dBm output causes distortion so there needs to be and amplifier for whatever you are using.

 

I also rather agree about the offset frequency, I always set it to 0Hz and then the spur is where your carrier would be in SSB. If the tx cal is done and the output level is not above -10dBm the spur is very low.

 

Maybe I was lucky with the hanging problem being solved by adding the 50ms tx delay, but it did fix it on the slower pc – I think....

 

This noise problem is the one that is causing me most concern at the moment particularly if you are running any power.

 

Mike

 

Sent from Mail for Windows 10

 

 


josephlevy
 

Hi Jose and Sigi
I can relate my experience with the LimeSdr USB

Do not transmit anything near the max power out.(signal is way distorted  then)
I set it to -20Dbm  (so needed another amplifier in the chain to reach the 2.4 Ghz for the Qo100)
But then it does not get stuck, no central spur (I use 250 khz offset) and see no spur anywhere on the full band of the Qo100)  (peak signal when modulating with a single tone S9+12
and nearly 37-8 S/N).
BTW   Jose I use now the X8 resolution on the waterfall and then you can see very accurately any Jitter in your signal, and mine is very similar to the band edge Beacon. If the 'lock to Beacon' is wobbling (a bit, not complete unlock) the you'll have wobbling on your TX freq.)

De Joe 4X1RV


Siegfried Jackstien
 

jose .. do not use offset ... not 25 and not 250 ... set that to 0hz!!

reason is ... that way the spur is next to your passband ... and you do not disturb on another frequency ...

(in my view simon should set default to 0hz)

dg9bfc sigi

Am 30.05.2020 um 14:21 schrieb jose maria trueba:

Yes. I have also seen very dirty transmitting most often and aclean signal sometimes. I do not know how.
Regarding the no transmission issue ... It used to happen quite often. Once every hour or so. Now with newest version of SDRC it happens very seldom with my i3 laptop running win10, maybe once every 5 hours, but if happens very often with my i5 running win7. I found out that transmission lacks audio, no Tune nor Tone either but if I push Drive all the way to 100% then I see that LimeMini is actually transmitting the DC central spur very visible 0.9KHz below the nominal transmitting frequency if TX offset is set to 0KHz instead the 25kHz default. 
By the way... How can I add your 50mw? I would love to try it.


MikeC
 

I have two pcs. On the fast one (I7) I do not see the no transmission problem, but on the slower one (I5) I seem to see it often. It seems to not stop properly at the end of a transmission and therefore will not start another. Stopping or closing causes the program to hang.

 

I found that on my slow pc selecting 50ms on the tx streaming delay seemed to fix the problem and I could not make it do it. I have attached a picture of the setting screen. It is in Options, Radio Configuration. I found that any non zero delay here fixed it. I hope it solves that problem for you.

 

This noise problem is very strange, interesting that you may have seen a similar thing.

 

Mike

 

Sent from Mail for Windows 10

 

From: jose maria trueba
Sent: 30 May 2020 15:21
To: main@sdr-radio.groups.io
Subject: Re: [SDR-Radio] #LimeSDR Transmit Anomaly

 

Yes. I have also seen very dirty transmitting most often and aclean signal sometimes. I do not know how.

Regarding the no transmission issue ... It used to happen quite often. Once every hour or so. Now with newest version of SDRC it happens very seldom with my i3 laptop running win10, maybe once every 5 hours, but if happens very often with my i5 running win7. I found out that transmission lacks audio, no Tune nor Tone either but if I push Drive all the way to 100% then I see that LimeMini is actually transmitting the DC central spur very visible 0.9KHz below the nominal transmitting frequency if TX offset is set to 0KHz instead the 25kHz default. 

By the way... How can I add your 50mw? I would love to try it.

 


jose maria trueba
 

Yes. I have also seen very dirty transmitting most often and aclean signal sometimes. I do not know how.
Regarding the no transmission issue ... It used to happen quite often. Once every hour or so. Now with newest version of SDRC it happens very seldom with my i3 laptop running win10, maybe once every 5 hours, but if happens very often with my i5 running win7. I found out that transmission lacks audio, no Tune nor Tone either but if I push Drive all the way to 100% then I see that LimeMini is actually transmitting the DC central spur very visible 0.9KHz below the nominal transmitting frequency if TX offset is set to 0KHz instead the 25kHz default. 
By the way... How can I add your 50mw? I would love to try it.


MikeC
 

Hello Group

 

I have a LimeSDR (not the mini) and in the course of testing I have come across this curious problem. On transmit it seems to generate noise over several hundred kilohertz, but not all the time. I think this problem has been there for some time but I have not been so aware of it. The noise is clearly band limited by the SDR and seems to occur virtually every time the transmit is keyed. However if you stop the Lime and start it again then sometimes the effect never occurs. Once the Lime is started, and the effect is not there, it is clear until the Lime is stopped and re-started. It seems to happen for more than half the “starts” although varies somewhat in amplitude. I have attached three spectrum analyser pictures, one shows the effect absent, one shows the effect present and the third with a frequency offset of 250kHz selected. I am sure this last observation is significant.  The signal and the noise vary in amplitude together with drive level. I have tried various things, sampling rate makes no difference nor doing a tx calibration. I have also tried a different pc together with buss power/external power with no effect. I do not believe it is temperature dependant either.

 

I tried at 50MHz, 100MHz and 144MHz and the result was identical.

 

The spectrum analyser is connected directly to the Lime low frequency output port.

 

I have also attached two screen shots, with and without the noise present. The other signals are coming from my 2m antenna by the way.

 

I ran up SDRAngel and could not replicate this effect although the whole arrangement is so different that the comparison may not be significant.

 

Receive seems to operate normally at all times.

 

As an aside, while testing on another (slower) pc I experienced the tx hanging effect which required a close and restart of Console. This occurred quite regularly until I added a 50ms hang on the tx streaming which completely fixed it. I don’t think this is related to this noise problem.

 

When working correctly the signal is so very clean and the whole arrangement works extremely well.

 

There is the possibility that the board I have is malfunctioning in some way, I cannot guarantee that this is not a new problem although I think I may have seen it earlier and not realised what it was. I don’t always have the spectrum analyser attached when you can see it more obviously.  

 

Has anybody else seen anything like this and/or can Simon suggest any other tests I can do to see what is happening?

 

 

Mike Christieson