26 June 2023

My Ham Messe Friedrichshafen 2023

I'm back from Friedrichshafen Ham Messe 2023 and it is time to sum it up.

Hall A4 at 1/3 capacity.
Hall A4 at 1/3 capacity at 9:18 day 1

Space usage was pretty much the same of last year, as I had documented for my future self on this blog. The crowd was more or less the same. We stayed from 09:15 to 15:30 on day 1, Friday.

Regardless of the shrinking (or not) of sellers and audience, Ham Messe is still unique as it gathers HAMs from all over Europe and the world.

What I bought:

  • an energy measuring device for home (5 €)
  • 8 sticks of machined pin sockets and 2 sticks of multiturn Bourns trimpots (2 €/stick)
  • two Z303C dekatrons (10 €)
  • a variable lab power supply with 8V, 18V, 80V independent outputs (25 €)
  • T-shaped BNC adapters to play with the HP counter (1 €/each)

What I haven't bought:

  • an HP signal generator "for parts" (probably working) we couldn't reach an agreement on the price
  • other gear that I saw leaving the hall at lunch time, I think withdrawn from owners not actually sold!
  • Nixie tubes at current market price
  • what looked like homemade HF RTX from HA and YU sellers, since I have no HF antenna at home
  • other aero DME receivers that I bought last years, too bad

That's it. Next year the Ham Messe will be held on 28-30 June, 2024, if it will take place.

Three more pictures.

Pretty early days vacuum tubes...

... quite recent lab instruments.

I didn't know of this initiative from the nearby city Tettnang.

23 June 2023

An HP 5326B enters my lab

It was just a matter of waiting until I could buy an old/surplus/vintage HP device with Nixies for little money. Unknown conditions, of course.

I bought an HP 5326B Electronic Counter in Basaluzzo HAM flea market (June 2023) which was designed to measure 100 mV up to 50 MHz and display the result on 7x B5750 Nixies (or similar). It also has a 1000Vdc voltmeter measured using an internal V/F converter.

Display board of HP 5326B.
Display board of HP 5326B.
On a first visual inspection the unit was serviced once to replace a 1820-0119 IC that was actually rebuilt with TTL ICs! It had loose screws of the top cover, so I wasn't hoping for the best but I powered it up nevertheless.

Well, well, it sprang to life and seemed to give proper readings, so I needed to read the manual to check for proper operation and calibration check.

The unit is in proper working order. The stock 10 MHz reference oscillator is spot-on at least for the precision I can reach in my lab. The DVM might be reading 1% high my calibrated voltage source, but I'm comparing it to other uncalibrated, various era, less resolution devices.

I like the possibility to make it count events until the reset button is pressed, which means it can become a clock with very simple interfacing.

The rebuilt 1820-0119 does not implement leading-zero blanking so the 7th digit is always on. I'm even thinking of building a modern replacement of the counter+buffer pair 1820-0119/1820-0116 by means of a microprocessor. This way I regain the leading-zero blanking and I might even add the 8th digit option!

I played a little game: how far does it measure beyond the 50 MHz upper limit? I used the NanoVNA as a frequency generator using the "CW mode" (alternatively you set the Span to 0). I have no idea of the signal amplitude at this point but it reached 95.000 MHz! The counter is 9.3 kHz high (0.01% or 100 ppm).

A visual proof that with enough input signal the HP 5326B can count up to 95 MHz
HP 5326B measuring 95 MHz.



17 June 2023

MEMS microphone with TDA1308 amplifier board - 1

A local HAM has asked me help to integrate a microphone module in his mobile setup. He was directed to the little MEMS/silicone microphone module shown in the picture below with very positive comments.

An electronic board with a MEMS active microphone and an amplifier consisting of TDA1803 integrated circuit.
MEMS microphone with amplifier circuit.

The problem with his initial setup was a wiring error in the RJ plug, but with that fixed the module showed an unexpected effect: even in complete silence the circuit would produce a strong hiss like driving at 100 km/h with open windows, and the modulation was extremely loud.

Digging a bit further on aliexpress I found a description of the circuit:

  • Working voltage: DC3V-5V
  • Output about 30mw, can directly drive ordinary 32 ohm headphones
  • R5: amplification adjustment resistor, resistance value can be used 4.7k-100k [cut] The higher the resistance value, the higher the gain [the board comes with 22k]
  • R6: for the microphone sensitivity adjustment resistor, shipping default for high sensitivity (resistance value of 0 ohms), the resistance can be selected from 0 ohms -10K between [cut], the greater the resistance value of the resistor, the lower the sensitivity

Very good information: the stock board has maximum microphone gain and middle amplification gain. 

I also checked some random datasheets from Knowles SiSonic product range and noticed that 5V is usually the Absolute Maximum Rating for their MEMS microphones.

He gave me one module to experiment with. Stay tuned!