BK 1856D Frequency counter repair

 I have a BK 1856d 3.5GHz freuency counter which was bought in the USA 20 years ago. It has been languishing in the wardrobe for 5 years as it wouldnt work on the GHz range via Input C but worked fine on the 100MHz Input A. This has happened before when i blew up the input modamp, i assumed the same had happened. Having some spare time it was time to investigate

First I removed the preamp module from the front panel. This required peeling back the plastic front  panel label near the connector and removing the four M3 screws

The circuit has 2 modamps feeding an MC12079 prescaler. The modamps (running off 5V) feed a diode detector,  the output of which is amplified by the LM358 opamp which is used by the logic in the counter to detect a signal at Input C

Firstly i measured the DC conditions of the modamps. Both showed 5V on the output and 1.4V on the inputs which looked promising. I then put a 1296MHz -30dBm signal into the N type and found a suitable amplifed signal at the output of the 2nd modamp. The modamps were good. I then looked at the output of the prescaler . Nothing but noise. The prescaler had died!

I found a replacement  MC12079 on ebay and replaced it. The counter now works fine. 

Protecting the K3 HF receiver when on 6m

 I noticed that when I transmitted on 6m there was relay chattering inside the K3 if I had the HF connected on antenna 1 and the 6m antenna connected to Antenna 2 as the K3 detected RF overload.

I realised this was due to the close proximity of the HF antenna and the 6m HB9CV, the separation being 10m horizontally

Initially I tried a quarterwave 50 MHz coax stub on the antenna 1 input but that didnt attenuate the 6m signal enough. I then moved onto investigating a homebrew 30MHz low pass filter

Searching the internet I came across the design by PA0FRI which looked promising so I opted for the 200W version. 

I bought a box of assorted value 1kV ceramic capacitors from Aliexpress but when I measured them only 2 of 20 came close to the printed values. So I gave in and ordered the values I needed from mouser which when were measured did what they said! 16swg enamelled wire was bought from Ebay.

 I searched for some ceramic pillars but as they were rediculous prices I 3D printed some M3 tapped PLA+ pillars and used m3 screws and solder tags to hold the components in place. I used SO239 connectors for input and output

Low cost SDR update (4) One is not enough!

 Having been impressed by the receiver I could not resist building another one, especially at the price! My supplier of the A/D board had a spare board and as G4BVY also wanted to build one a receiver for skimming purposes so we combined orders

I also discovered GI4DOH had designed (after many iterations) a 3D printed box that was a custom fit to the board stack so I managed to get the .stl file from him and I printed one (took 4 hours (box and lid) on my 3D printer

The printed box was much smaller than my diecast box and was unscreened. I also could not see a way of getting a switcher PSU  in the box and heatsinking it so i continued with the external 5V PSU supplied with the FPGA board

The box also has provision for a fan. I fitted one but have not needed it yet

Low Cost SDR update (3): Multimode skimming

Having got all this data from the Receiver it obviously needed skimming. My current desktop, a 5th generation I5 would not have the power so I started to look around. I consulted GI4DOH what he used but G4BVY discovered an Intel I7 Gen 11 NUC at a good price so we ordered one each.

When mine arrived I was stunned at how small it was! Its features were 

"Intel NUC 11 NUC11PAHi7 32GB DDR4 RAM,1TGB SSD,Win 11 Pro Mini PC,Corei7-1165G7 Processor"

  

Initially I decided to set it up for 8 bands of cw skimming and 8 bands of RTTY skimming. The instructions were at https://pavel-demin.github.io/qmtech-xc7z020-notes/sdr-receiver-hpsdr-77-76/  and were easy to follow. It worked fine but not much RTTY action.

Skimmer server CW (8 bands) + RTTY skimmer (5 bands) +Aggregator

To stress the computer a little mor, for the ARRL RTTY contest i set it up the same way (8 x CW 8 x RTTY) and decoded a lot of RTTY signals but CPU useage never got above 35%