3.4 GHz Transverter Conversion (3.5 GHz WiFi transceiver)

[VK5ZD]

Also, for the -50dBm input (@3400Mhz) when testing/peaking the rx, what sort of output is everyone getting at the 444Mhz side to the transceiver?
Or, with -50dBm input what rough S reading are people getting on their radios - noting that S meters on radios can be vastly different (lets not get into THAT debate ).

S9 is -93dbm, so -50dbm is S9+43db.
An S1 signal would be (theoretically) -141dbm. In practice, S-meter readings are pretty much meaningless, especially when using a transverter.
The probably exception to this would be if you're using a SDR and have factored in the transverter conversion gain (or loss).

Either way, as Tim says, -50dbm is a massive signal and should be 'bending the needle' on your S-meter.

[VK3HY]

As for the Tx switching.....

The low dropout 5V regulator supplies power to the comparator IC. Note that +5 is on Pin 7, output is pin 6 which is LOW for TX.
Pin 3 should be around 2.5 V and pin 2 around zero until DC is applied via the resistor. When pin 2 volts exceeds pin 3 the output goes low.

(Note that in my mods where the micro controls the TX, I bias the comparator into TX mode then rely on the other control input to that circuitry from the micro....)

Any questions...just ask.

Tim VK5ZT

Dear Doctor Tim

I also have a Panel that will not switch to TX.
I checked the voltages as per your note and found that the voltage on Pin 3 of the comparator IC to be 4.5V not 2.5V. When DC is applied via the 4k7 resistor, the pin 2 volts do not exceed pin 3 volts so the output pin does not go low as required for switching to TX.

Voltages measured are:

Pin 7 +5V TX/RX
Pin 6 +5V TX/RX
Pin 3 +4.5V TX/RX
Pin 2 0V RX & 4.3V TX

Any ideas/suggestions?

Gavin, VK3HY

[VK5ZT]

Hi Gavin

Your problem looks fairly straightforward. Looking at the extract from the GARC publication, you can see that the voltage on pin 3 is obtained by using the two 1 meg resistors as a voltage divider giving 2.5 volts. If you are getting 4.5 volts on pin 3 maybe the bottom resistor of the divider chain is not connected or open circuit. Since the mod requires you to add that 1 meg resistor I would look closely at that. The only other possibility is too low a value for the other resistor but since you are not required to move that I am assuming that is not the case.

Hope this helps....


Tim VK5ZT

[VK3HY]

Hope this helps....


Tim VK5ZT

Thanks Tim....your 'prescription' was spot on. The lower 1M resistor of the voltage divider was open circuit. I guess I damaged it when moving it as per the GARC modifications. I now have a healthy looking 30.55dBm tx output.

Thanks again
73 Gavin, VK3HY

[VK4EA]

I thought I had finished a panel for our 23 on 23 day yesterday, all tested out fine on the bench with a signal source, output looked clean on the SA etc, ---- SNIP ----
OUCH Peter. Well you'd think it was a mechanical problem if it happened after a fall but I have had one dead LM2676 - you could try there.

Lou, spot on, the LM2676 input was a dead short to the 12 vdc supply. New items ordered from XON.

[VK4EA]

add that 1 meg resistor I would look closely at that. The only other possibility is too low a value for the other resistor but since you are not required to move that I am assuming that is not the case.

Tim VK5ZT

And rather embarrassingly, this was exactly the case with my issue as well, I reluctantly used my binocular microscope to inspect my soldering, was to say, errm, was rather dodgy. All good now now both sides of the 1M resistor are connected

[VK7HH]

I've started conversion on my 3.5GHz panel after being donated it by Matt VK3PP (thanks Matt). I was motivated to convert one after Peter 7PD's contact earlier this week with Chas 3PY over Bass Strait using one.

I'm now up to the stage in the manual to test the 3.4GHz RX/TX before going onto installing the switcher, which is yet to arrive from Lou 3ALB. I have hit a speed bump because I don’t have any means of measuring output power at 3.4GHz.
I also don’t have a signal source, my HP8924C will only go up to 1GHz. I did do some tests though and the board powers up, and draws about 350mA on receive. TX current is about 850mA with -4dBm on the IF TX input so that sounds good. I can see it vary a little when I adjust the input up and down on 444MHz from my signal generator too and the beeper goes nuts.

I did try a quick test with my sig gen on 850MHz and hoped for a 4th harmonic at 3400MHz but I think my test set is too clean. At maximum 16dBm output connected to the RX input I can’t get the beeper to go any faster. I also don't have a handheld that will go down to 425MHz to use as a signal source.... I used to have a Baofeng, perfect harmonic generator, but I can't find it now

I can pop the sig gen on 444MHz and wave the probe around near the UHF IF filter and the beeper starts going crazy, so from that point onwards seems to be working.

Now to see if I can find a screwdriver small enough to adjust the trimmers on the UHF filter board.

Regards
Hayden VK7HH

[VK7HH]

Conversion update -

Tested the board... The good news is it's receiving. I think it's receiving well too. Measured down to -120dBm at least, on FM. USB it could be heard even further.

I tweaked the RX and former TX filters. I don't think I can get much more out of them. The UHF trimmer made a HUGE difference. Brought the noise right up.
I can also hear a signal when generating 850MHz from my test set. 4th harmonic at 3400MHz.

However, there is some bad news. I measured output power and it's only 125mW, probably 150mW maximum. I suspect I didn't realize and left the PA open circuit for a short amount of time whilst current testing. One of the FETs is probably blown.
I'm not 100% sure whether to try replacing the FET or just live with the output and use it to drive one of those "Stealth" amps. There is plenty of drive there to get 20W out. that way I can make it a full transverter, box it up, maybe GPS lock etc. and just use the panel antenna, or an alternative down the track.

[VK7HH]

A further update.

My Stealth amp has arrived in the mail yesterday. Really fast turnaround, only took a week and a half from Israel. So now to get that wired in.
Are there any surplus panels floating around? I'd like to try to generate a bit more interest in VK7 with these panels.

[VK7HH]

Panel re-boxing is almost complete. Just final adjustments being made. I added a Minikits sequencer and a Mini-Circuits preamplifier. The unit seems to be receiving very very well.

Interestingly I had issues with no output from the panel after I changed the RG-142 to 0.085" hardline on the TX mixer IF input. I redid this connection and generally cleaned it up a bit around the board. After doing this I now measure 32dBm out of the PA, which is amazing considering I only had 20dBm before. Perhaps I had a really bad connection on the IF side.

I also opened up the panel today to redo the connection and put an SMA connector on the cable. Below is a photo for interest.

[VK3ALB]

Nice one Hayden,

Hang on to that panel if you can. It's a pretty good performer and has 18.5dBi gain. Chris VK3ACG has run his at 50W on several outings now with no ill effect or indication that it it is overheating. You're probably looking to build something bigger but it's nice to have a smaller antenna for that quick local contact. Don't forget Peter and I worked over 420km with panels and there was still plenty of signal.

MTI_405013 3.4GHz panel.pdf

(130.22 KiB) Downloaded 360 times

[VK7HH]

I reduced the output power by driving the panel from my test set at a much lower level. I then measured 0dBm on the output of the transverter and fed that into my SM3437 amp. The end result is a nice 22W output (although I did cook a 10dB pad by mistake - 2W not 22W rated ).

Once external attenuators arrive then I'll place them on the input to the amp.

Some have commented on the microphonics of these boards. I could tap the case/board when it was mounted in it's original configuration and easily hear it in the speaker of the radio. However since mounting on the aluminium plate as I have done, it has either reduced it to a level where I cannot hear them anymore, or gone completely.

I just used metal standoffs and made sure everything was secure and doesn't rattle.

Next step is to now pop a connector on the back of the patch antenna and mount in some way to the rear of the case or lid for easy portable work.

[VK7HH]

GPS locking the GARC transverter:

[VK7HH]

Low receive performance on your GARC panel?

Kindly provided by David VK5KK, here is a couple of mods that can be done to your panel to increase the receive sensitivity. This has been personally done and tested on my panel and it's made a huge difference.

3.4Ghz Panel - Low RX.docx

(1.73 MiB) Downloaded 350 times

[VK7HH]

Wanted: GARC 3.4 GHz panels. Is there anyone with a spare out there? I want to convert a panel for use as a beacon using Tim's standalone beacon code. Of course, if there is someone willing to program such a board for me, that would be even better!

Even if you don't have a spare, but do have a unconverted panel, now's the time to get the soldering iron out and convert it!

Alternatively, even after just the panel as an antenna!

[VK3ZSJ]

Hi Gavin

Your problem looks fairly straightforward. Looking at the extract from the GARC publication, you can see that the voltage on pin 3 is obtained by using the two 1 meg resistors as a voltage divider giving 2.5 volts. If you are getting 4.5 volts on pin 3 maybe the bottom resistor of the divider chain is not connected or open circuit. Since the mod requires you to add that 1 meg resistor I would look closely at that. The only other possibility is too low a value for the other resistor but since you are not required to move that I am assuming that is not the case.


TX Squelch.png

Hope this helps....


Tim VK5ZT

thanks for this post. i found myself to be in the exact same situation and it was my lousy soldering at the bottom of the 1M ohm too. rgds