Harmonic operation


#21

Yea … id expect usability of LimeSDR @ 140Ghz to be nill (thats like a 38th harmonic – id guess past the 9th is dreaming)
… even if all the components outside of the LMS7002 were removed and a I/Q pair was routed from waveguide to the board traces would still be impossible.

But going by the inverse square rule ( i think its called) of a square wave harmonics … that the 3rd harmonic should be roughly 10db lower than fundamental (my Avatar show another SquareWave Lo with mixer in action) …

The usability of the LimeSDR @ 10Ghz still needs to be quantified – What is the 3db and 10db loss of the LNA – perhaps thats already known and has been used at 3.8Ghz …

I am getting something at 10.368 Ghz from the Gunnplexer unknown 13dbm output. might be more, might be less … its well within the scale of what i see from my HF antenna …

I would expect to use an external LNA as there are better LNA out there than what is used in the LimeSDR


#22

You got it almost all wrong :slight_smile:
I said that LimeSDR on 10Ghz is almost unusable. Do not even think going higher than that.
Just to compare how much loses at 10Ghz you have all together in such a harmonic receiver try the following:

Use some 200 Mhz signal or some 144mhz signal with 10dBm near the same LimeSDR antenna that you used to pick up the 10Ghz. You should use even more power if you calculate the gain of the horn you had on Gunplexer.
Measure the signal level at the Lime SDR (try not to damage the limeSDR frontend) and the difference between this two signals are losses in you receiving chain (limeSDR used as harmonic mixer on 10GHz)


#23

I would use an antenna meant for the band wanted … the Wifi is all i have at the moment – loss there can be reversed with the correct antenna.

Once i put my LimeSDR and Odroid-C2 back together ( i’m looking for a suitable case that i don’t need to cut a bunch of holes in) … Ill probably reassemble it like it was just to get a video of the signal difference when only changing to a harmonic and nothing else …

First video here is not quite what you propose … but is fairly close. The harmonic Rx of 162Mhz (lime set at 54Mhz) is not in the noise – as its called.

The Gunnplexer does not have a horn on it … its not in my video either. ( loss of signal out of the Gunnplexer due to SWR mismatch is not of concern i don’t think)


#24

It is difficult to evaluate exactly the performance as you are in the near field messing with the antennas.
The way how to find it your LimeSDR is performing as a Harmonic mixer on 10 Ghz is simple:

Tune the signal you are transmitting from a gunplexer or from that automotive 10ghz radar DRO device.
Change the LO LimeSDR frequency from 3456 to 3455 MHz.
The signal you were receiving on 10368 should be received now on 10371 or 3Mhz higher from 3456 MHz.


#25

Im not sure near field is accurate … i did that same thing before … and since its known from the 60’s that the 3rd harmonic is 180deg out of phase in relation to the fundamental …

At microwave frequencys … when are you out of near field. the wavelength is so short. I did previously point the Gunnplexer away at arms length and was still visible on the display in one of the videos.

I think the real way to know if this Rx with the 3rd of the Lo and not a 3rd of mixing of the LNA is to get a transmitter or signal that would be within the second and 3rd harmonic range of LimeSDR. Then looking at the signal level of the fundemental, 3rd and then the second. If the 2nd is roughly ~40-50db lower than the fundemental … then its harmonic of the square Lo … if its high then its a harmonic produced in the LNA.


#26

Here is a comparison of fundamental and 3rd on indoor 2Meter antenna … of NOAA 162.4Mhz

I had cut the connector off of my outside antenna and pulled the coax outside … moving stuff around and cleaning up … and couldnt push the coax back inside since the hole was filled in … moving every thing.


#27

Too bad i didn’t think of capturing on 2nd harmonic frequency of 162.4 … ill go back to the garage and see …


#28

#29

I have done a bunch of testing and see results all over the place… Nothing that really convinced me there was a signal.

So I set up my GPS locked signal source at 2.592 MHz. I see a very strong and quite clean harmonic on 10.368 MHz on a couple of rigs here.

I have put my Lime in a case. I was seeing all kinds of weird signals with it in my acrylic case (as I would expect). I then hooked a WR-90 transition to it.

Here’s SDRConsole tuned to 3456 with no signal. Center spike as expected.

Then, here is the signal generator turned on. Some sort of signal at 3456. I didn’t hit “auto” on the waterfall, so the high phase noise is not showing.

Then I tuned SDRConsole up 1 MHz to 3457. Signal moved to 3460. (auto on waterfall) Image at 3454.

Then I tuned SDRConsole down 1 MHz to 3455. Signal moved to 3452. (auto on waterfall) Image at 3458.

LOTS of phase noise… So it looks like there is something there. I wouldn’t consider it usable. I can do many times better with a simple Avenger PLL locked LNB for $10 with the Lime tuned to ~ 618 MHz…

I did check my signal source that way and to avoid overload on the Lime, I had to insert 30 dB of IF pad between the Avenger and Lime and set the Lime LNA at -30 and I still saw about 50 dB of signal…

Mike


#30

Weird, i still wonder what connector on the board your using …

I get almost 50db difference from noise floor to peek before the phase noise comes into view … (about the same as i do from a close 2Meter repeater level)

I also removed the 2pF capacitor from across the I/Q lines … – that didn’t seem to change much.

Wonder if there manufacturing differences (variations) of the LMS7002.

There shouldn’t be a signal large difference from using Linux/Ubuntu/Gqrx and windows/sdrconsole.

Does your signal source have that kind of phase noise (seen on a spectrum analyser ) … or is it something else . It reminds me of AM.


#31

I used the W port. I checked all to see which was best.

For comparison, here’s the $10 Avenger LNB with the same WR-90 transition hooked to it. Same signal source.

I inserted 30 dB of pad between the Lime and LNB and you can see I also have the Lime LNA gain set at -30 dB (all the way down).

Signal peaking at -34 dBm… That’s what the signal source looks like.

Is your Lime in a case? When mine was in the acrylic case, I saw all kinds of weird signals - some very strong - by holding the signal source above the Lime board. Also saw signal getting via the USB cable.


#32

On mine … The H port has the best signal … Rx1_H – farthest right/top with USB away.


#33

Still no case … but did use 3foot of some micro hardline that iv had for years … and tied it to a HB100 pannel antennas (also disabled the path to its DRO/amp)


#34

Mike, so it is a classical harmonic mixer on 3cm, with a lot of losses.


#35

You are right, I did use the H port. It’s the top right on my case.

Small fan just arrived. Now to get that installed.

Also got some 0402 zero ohm resistors. Next is to modify the RX1_H port by removing all the caps leaving the transformer. Then we can sweep it with a VNA. Possibly come up with some decent matching networks for 902/1296/2304/3456.

You mentioned removing a 2 pf cap? I see 2 in series on the RX1_H port, but the the shunt is 1pf??


#36

Yup, classic with emphasis on “Lots of Losses”. Not really worth the effort to work with IMHO considering cheap options available for receiving 10 GHz really well…

Possibly the LMS8001+ will work - if and when we see it.


#37

I would think that different LNA’s and mixers for the 3 ports would do …
The H port use parts designed for ~15Ghz

The L port have blocking capacitors that are more suited for 100Khz up to 500Mhz


#38

I keep for getting to ask you N1JEZ

You have attenuators … could you add more attenuation, like 5db or 10 and relay the displayed change?

I once did this – but cant remember what band, and it was not 10db of display drop per 10db added on gqrx


#39

Well … iv been up to a bit more …

I think N1JEZ blew out the LNA in his board …

How far away do you need to go before your out of Near Field on 10Ghz?


#40

How far? 2x D squared / lambda
I think you have something wrong there. The signal you have from the DRO radar device is too stable and the signal does not change when you move your hand around the antenna. You should note the dopler in frequency at least, plus fading in signal.