Saturday, December 18, 2021

HP 3312A small repair

 No big troubleshooting here, the HP3312A function generator had been developing small fault over time, the last time I used it was not outputting signal or with the wrong shape, so decided to see what could be done.

This was the "sinusoidal" output:


Not good! Also the frequency was not in line with the bezel markings.

Here's the offending component on top board near the front panel.

I just guessed it was the one causing the issue, the crack was easy to spot.

The reference marked in the capacitor, if needed:

TRW 8508
.5MF +/- 10%
50 VDC

Better now after replacement, I didn't had 0.5MF as originally so by mistake placed a 2.2uF, got better but still some distortion seen:


 I then replaced by a 1uF one and now it's perfect, in the future I will probably try to find the right value (0.5uF) and replace.

Have a nice day!

Wednesday, December 15, 2021

PGA103+ Ultra Linear Low Noise Monolithic Amplifier

Had this little device for some time, an offer from a fellow ham some time ago (thank you Allan).

Schematic used is similar to the datasheet at:

with small changes (similar to, in the implementation I didn't included the front end diodes:

  The PCB was done with very few resources so it had to be tinned.

Basically made with a mix of vinegar and oxygenated water

On the sweep on the spectrum analyzer this is what you get.

 Will try this further on as fronted for a VHF/UHF radio.

 Other sources of information with more comprehensive details here: 

(includes an HPF design for 130Mhz)

Have a great day!

Sunday, December 05, 2021

10Ghz downconverter for 1.5Ghz spectrum Analyser

Had this build for some time, now it's time to show. 


 I was doing some experiments on the 10Ghz band and wanted a way of looking at the signals. Because the spectrum analyser I have only good to 1.5Ghz had to find a cheap way of doing it to get this:

Here looking at the third harmonic from an ADF4351 on 3.3Ghz after a pipe cap 10Ghz filter experiment.

The diagram explanation: a dbm mixer (Watkins-Johnson M80LCA) with a local oscillator based on a FVC99 10Ghz oscillator module (cheapest VCO I could find for 10Ghz). Some preamps on the input and output using 2Ghz preamp modules and replacing the MMIC amplifiers for the ones like Corvo NLB300 or ERA-1 that are good to 10Ghz.

The basic design:

 To this diagram I added a 6db directional coupler inline with the FVC99 VCO (used a Omni Spectra PN2023, good from 8 12.4Ghz) so I could measure the LO frequency and PLL it.

There is no stability control on the FVC99 oscillator, still working on a PLL system (maybe one of these days) but in my case I have two select positions, one: VCO is controlled by a single pot (like on the diagram) and the other position controlled by an EIP371 frequency counter (from the Lo Out via directional coupler) that makes the PLL loop. With EIP371 and since the output voltage of the loop is very small the control range seats near 9.5Ghz, there is an option of extending the range like on the EIP manual:

Or with a similar diagram, a multiply by 10 of the PLL voltage out of the EIP371, that would be enough to use the full range of the FVC99.

For now I use 9.5 Ghz if using the EIP371 for more stability and around 10Ghz set by the pot ("Flo" on the panel) if it's just a quick test.

Here the EIP working as external PLL controling the FVC99 so the LO gets more stable.

On the Rigol DSA815 spectrum analyser you can set the input offset to get the display right on the band of interest

Displaying here a 10Ghz signal using the 9.5Ghz Lo frequency

If you want to just check if the signal is around there, no need to use external PLL control to the FVC99, the "stability" with a simple potentiomenter  is enough.

Inside view:

The VCO adjust pot (top right in blue) is glued directly to the front panel

Some other images during prototype development:

Here one of the firsts tests, just an input amplifier, the mixer, the VCO and VCO amplifier and the mixer IF output directly to the spectrum analyser.

Testing during early days of the prototype with a 10Ghz homemade flange to SMA adapter and a pipe cap filter:



Anyhow, not a measuring device but it serves the purpose of checking if you have any signal around the 10Ghz band and for experiments, still very happy with the outcome and sensitivity.

Have a nice day!