Posts by DF2HF

This may be a silly question, but if you can't open it while powered on, then how do you troubleshoot an amp like this (when you need to measure voltages across different parts of the circuit)?

Thanks G0MJW

I will stop testing this amp until I make proper heatsink.

Out of curiosity: is it also important to have the proper ground/heatsink for a quick passive power-on test? Will it still do this self-oscillation? My initial assumption was that it's safe just to turn on the amp without driving it.

PA3FYM Thanks. I was aware of it. In fact I just soldered the isolator in place (and will take care of the ground)

DB8TF Sure, but 0.35V ?! It's so low that I can't reproduce the expected idle current (0.8-1A)

So the left transistor has bias issues (the bias voltages for the right, including the V201 pinout readings match G8UGD 's schematic)

G0MJW Thanks for your time.

Well, I'm also a beginner to microwave. My experience in this area is limited to my QO100 setup (this is the 3rd amplifier I'm tinkering with, after the Chinese WiFi booster, and the other Doherty amp)

The voltage at drains seem to be normal (28V), but the gates are 0.4V and 0.5V, so you're right about the threshold and that's where my problem is.

I've attached some pictures. Please note that this is not my final setup and I'm not gonna use it like this. I just wanted to make sure that this device is not faulty, and only then I would spend time on a proper heatsink. So no RF input is given to it. Just idle measurements.

Also as you see in the pictures, the sources are not grounded, so before I do the test setup, I connect the source to ground manually.

These modifications are according to the manual provided by the seller (removing the capacitor in the input, doing 2 snowflakes, cutting some traces in the output path, and removing the final isolator)

Regards

G0MJW Of course not. I attached this picture to distinguish this question from the previous ones talking about the other amp.

Hello everyone

I faced another weird issue, but this time on another amplifier.

The idle current should be around 1A, but it's only 6mA !!

When I touch the gate of the transistor at the top of the picture, the current increases to 1A.

What can be the issue? I'm checking all the connections. The only thing I can think of is a loose connection to ground somewhere.

Any ideas?

Bests

One more update: I cut BLF6G22L`s access to N100 and provided an external voltage directly to the gate.

This caused the idle current draw to increase from 200mA to 1.4A and also increased the output power again, so the problem exists in that section, but I think I have messed up something because the output is a little bit distorted and has an echo in the voice.

Thanks. I will do that as well.

In the initial tests, I couldn't find a bad capacitor.

I measured the voltages on Gain and Drain of every stage.

It seems there's a problem in either N100 or N110, because I don't have a voltage in the gate of BLF6G22L.

Going to test more and will update you if I manage to find the issue.

Thanks DB8TF

I will check the capacitors today and will follow those posts.

I was initially concerned that I have damaged the first stage.

Is it safe to remove the faulty bias capacitors entirely and not replace them?

One more thing: the PA's idle current has dropped from around 1.4A to 0.3A !!

Seems similar to DK4FT 's problem

Did I just damage the driver of the PA?

Hello. I ran into an issue with this amp today.

For 2 days, I was running it and had many QSOs with strong signal reports and clean output modulation.

Today I did the same, but in the middle of a QSO, suddenly my power dropped a little bit and my voice became distorted!

I have checked everything and even changed my SDR to make sure the problem is not them.

It seems the PA is in an under-drive mode. If I set the TX gain on SDR Console to 100, it works and the output signal is strong, but it's distorted. If I reduce the gain, my signal becomes very weak!

I provide ~25dBm to its input.

Any ideas? Is it possible that the input stage of the PA is damaged? How can I best troubleshoot it?

Regards

Mehdi / DF2HF

Thanks DK8KW

I decreased the gain but the problem still exists. It's just getting very weak. I'd like to find out the source of the issue. Is it a problem in LimeSDR Mini's FPGA code?

Bests

Mehdi, DF2HF

Dear OMs

I have encountered an issue but I don't know what's the reason:

When transmitting with LimeSDR Mini, I see a constant tone in the background of my signal, but I don't have the same with PlutoSDR. To show you the difference, I made screenshots with a muted microphone while transmitting. As you see Pluto has a clean signal, but LimeSDR Mini still has that tone (although the mic is mute)

All the hardware and software setup are the same (SDR Console latest version with the same config, CN0417 pre-amp and also the same PA)

Have anyone else made a similar observation? Do you know what's the source?

I have also attached 2 pictures of the output of the two SDRs connected directly to spectrum.

73

Pluto connected to spectrum:

LimeSDR Mini on spectrum:

Pluto on QO100 WebSDR:

LimeSDR Mini on QO100 WebSDR:

PA3GUO I don't know. I will test it more and share the results.

Today I tested it on-air. The amplifier gets hot, so I put it in the balcony. I also connected the output to spectrum analyzer (see the attachments)

Update: I increased the voltage to 27.6V (the maximum I can get from the power supply) and could get 44dBm output at 10A

Thanks to everyone for your help and replies. I finally tested the amplifier and it works (without any mods)

I used a SMA-to-AFI adapter for output, and made a SMA-to-MMBX cable for the input, so I don't have to desolder the existing connectors.

I used a 24V Meanwell.

The idle current is 1.8A

With ~10dBm input, it produces 36dBm.

With ~20dBm input, it produces 43dBm and draws 9.8A. This is enough for me for now. I may increase the input a little bit and get 1-2dBm more.

I didn't feed it with more power, because I lacked the equipment (my power supply is 13A, my ammeter is 10A, and the power wires I used are not safe for more than 10A)

Next step is to test it on the air!

It gets a little bit hot but I guess it's Ok. I've attached a picture (the outside seems to be around 52C in less than a minute)

PA3GUO @OH3WE @G3XOU

Hey. My connectors arrived today and I'm ready to test. Can you please give me some info about how to supply voltage to it? Based on the pictures, it seems I should just connect the two connectors across the board and then connect them to power supply, except the pin 1 which seems to have a different voltage (It's not connected to the other 4 pins in the line).

OK I measured it again. With a CW tone at 2.4GHZ I get 33.3 dBm.

In SSB and maximum drive and gain, I get 34-35 dBm.

Quote from HB9SKA

This WiFi booster has an amplification of about 10dB. This is the reason why you are not happy with it. 35dBm are too much, about 100 mW are real.

I'm happy with it to use it via NB transponder. 73

Hey Thomas.

What do you mean by "100 mW are real" ?

I have attached a picture of my setup and also a picture of my antenna's VSWR.

I've measured the output of each step with an RF power meter.

Output of LimeSDR Mini: 8-10dBm

Output of CN0417 (which is connected to LimeSDR): 27dBm

Output of the WiFi booster (which is connected to CN0417): 35dBm

My cable has about 1dB loss and my antenna's VSWR is less than 2.