Electronics > Repair
Aeroflex IFR-2398 / calibration / repair help
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andy_silicon:
So - focussing on the high end loss.

I've retouched a couple of dry looking joints and firmly pressed all the rf absorbers down.

Now I have 8db loss at 40Mhz and 22dB at 2.7ghz.

I.e. I lose 14db from 40Mhz to 2.7Ghz. Getting a little better.

BTW all my measurements are with the E4406a VSA at the target frequency and NOT using a wideband power meter.

( the source is an E4437B - and I've accounted for losses in the cable ).
The generator and vsa are known to agree closely within 0.2dB
( when connected by a very low loss N hardline )
KJDS:
That big frequency slope suggests it's a problem up to and including the first mixer and it's LO.
andy_silicon:
Last time I measured at the attenuator output it was flat.

So that leaves the first preamp and that 'bodge'

What about the carrier null at the first mixer - could that show as this ?
( I've left that area untouched - but no guarantee the previous owner hasn't had a tweak )
G0HZU:
I'd advise against meddling with the LO null circuit just yet... I would expect that its function is to boost the isolation (at around 3.4GHz) between the LO port and the 3.4GHz IF1 port on the mixer. It looks to have two trimpot controls in a pair of microstrip tuned sections.

The net idea of this is to presumably to have control of both amplitude and phase at ~3.5GHz in order to deliberately leak the 3.4GHz LO energy across to the first IF such that the leaked signal cancels the internal LO1 leakage in the mixer itself. Without this circuit, if the LO1 was able to leak into IF1 at a reasonably high level (when the LO1 is down near 3.4GHz) it could get amplified in the two IF1 amplifiers and overload the second mixer.

Also the noise sidebands from the LO1 (when tuning down near 3.4GHz) could leak across into IF1 and mask weak signals. So this null circuit is presumably adjusted to null the net LO leakage into IF1 at about 3.4GHz.

Note:
What is a bit worrying about this analyser is that it appears to rely on NVRAM to hold all the factory calibration data. By contrast, all the analysers I have here have a hard coded (default) factory calibration that doesn't rely on a battery. But you can run a user calibration at anytime to allow the analyser to self calibrate all its attenuators and filters etc to allow the storage of an enhanced 'user' calibration and this is backed up in battery backed memory.

So in my case (HP or Advantest analysers) it's no big deal if the (rechargeable) battery fails because you replace it and load the hard coded factory cal data and then run a user cal after that...

But your analyser looks like it will lose all calibration once the battery goes flat... Not good!

If I were you I would contact IFR in the USA with your serial number and ask for all the hardcoded passwords and if it is possible to have access to the original factory calibration data file (for your serial number) so you can reload it into your analyser if your battery has gone flat.

If your battery is NOT flat then be careful not to short it accidentally because you will lose all cal data on the processor board!

I doubt they will let you have their little software program that lets you dump/load the cal data so you may need to reverse engineer the commands to allow a read or load of cal data. If you know anyone who works in a decent cal lab in the UK you might be able to sweet talk them into giving you their copy of the IFR cal software because I assume they must need a copy themselves.


G0HZU:
In my case I found IFR UK and USA to be very helpful with my old Mi2024 sig gen.

The IFR UK office put me in touch with the IFR USA office that deals with passwords etc and they asked me to phone them at a specific time with my serial number on hand.

They then told me the unique/permanent 'master' password inside my sig gen that overrides everything else. They also sent me the full service manual in pdf format at a time when it wasn't available on the net.
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