Batboard

Hi to all,

I had a problem with my 2975's generator.

The problem was identified, a mmic was burned at the output of the generator module.
The supply resistances are also damaged with it, as the MMIC has shorted.

I ask you if any of you could tell me what kind of MMIC is:
On the component is written H1.

I tried a MAR1 but it doesn't go up to 2.8 GHZ.

I suspect it could be an ERA1.

Could any colleague help me understand what component it is?

may actually be a discrete device.

You may want to reverse engineer the schematic around it and you may find there is a bias adjustment.

I think it may be the same device as used in the IFR 1900 output.

The bias adjust was for AM mode to get it in the middle of it's operating range.

"just to be clear the output device is NOT and MMIC but a discrete device GaAs HFET that needs to have the bias adjusted as part of the replacement.

The output needs to be biased in the linear range in order to correctly pass AM as well as the other complex digital waveforms used in the cell phone testing area."
Maybe be a SHF-0186 or SHF-0186K

Hi JRY,
yes I have found and I confirm that it is the part that you say.

I've already ordered it, as soon as it arrives I'll update you!
I also had to order the resistors and inductor that feeds the SFH0186, as it went short and caused these components to break.

Thank you

JRY sorry,
could you tell me the adjustment procedure for 1900, I think it is identical for the 2975 of which I can't find the manuals.

The spare part I found is the SHF-0186 do you think would be okay if it were the SHF-0186K?

The parameters seem very similar.

you may have to run the module outside the unit.

Input a signal mid band at 100% modulation or there about and adjust the bias to get the same modulation and minimal distortion.

At least that's roughly what I did on the 1900's output module.

I used the typical 8902A with the power sensor but an 8901b would work as well

OK thank you.
In order to perform the adjustment I managed to make a hole on the chassis so that I could access the adjustment with the card mounted.

Regarding the differences of SHF-0186 and SHF-0186K what do you think?
They look very similar to me.

I'm waiting for the components, as soon as they arrive I will be able to run the tests.

doubt there is much or any difference ....have not looked at the datasheet though

I mounted the new SHF-0186, the new resistors but I'm waiting for its inductor.
I put a temporary inductor to run a preview test and the tool works perfectly and the levels are correct on the whole band.

Without adjusting anything I get 4-5% distortion at 100% modulation and an error of about 6-7% on 100%.
I seem to be the parameters I found before the failure.

As soon as I have the inductor I can try and adjust in trimmer to see if it improves.


I update you when work is completed

Inductor arrived, I mounted it and everything works perfectly.
I made a small adjustment on the nearby trimmer and the distortion improved.
I can therefore confirm, that if this problem should occur, it will be necessary to replace this component:

- N.1 SHF-0186 or SHF-0186K (I have mounted SHF-0186)
- N.2 18 Ohm 1/2W smd resistor (CRGS2010J18R)
- N.1 10 nH high frequency inductor (MLG1005S10NJT000) observe the mark director towards the resistance.

Generation levels are correct.

I hope this experience can be useful.

I thanks JRY for telling me how to make the adjustment to get the least distortion.

Best regard
Gianfranco, IW2NXE