13 July 2018

Nagoya UT-106 modified for UHF only

Over the past days I could spend few minutes with the UT-106, study the problem and solutions.

1. Magnet.

The magnet is stuck to a metallic spacer that is supposed to be glued to the antenna base. I re-glued it and reapplied the adhesive paper: it seems it holds better now.

2. Length.

Some reviewers report that the UT-106 is not cut for HAM radio bands, but resonates higher (so it is too short). I don't have a proper connector adapter to measure SWR but I trusted those reviews and applied what I originally wanted to do: cut it to a 1/4 wave on UHF just below the upper coil. The lower coil is still there, but the resulting antenna is stiffer and does not wobble freely, which means it does not pull the base all the time. As for SWR, 3 metres of RG-174 cable introduces enough losses that the transceiver won't notice an antenna mismatch.

3. Testing.

First on-air test was positive as I could hit the repeater from the underground garage, which is not possible with the UV-82 stock antenna.

Second test was on the road. I could see the antenna through the glass roof and it is stable even on bumpy asphalt at 60 km/h. Signal reports from the usual friends were positive as they know how I got through every morning with the rubber duckie.


Third test at high speed. The antenna is positioned above my head and I can see it through the glass roof. My car has no flat metallic surface, so the small base does not touch 100%. At 117 km/h the antenna begins to vibrate: probably a bit faster and something bad happens. I can try to fix this with a small spacer that reduces the front-back empty space, but that's low priority considering that I rarely drive out of town and speak on the radio.

Fourth test at "DX" distance. This surprised me most. I could hit my usual repeater from far away, through a valley where I could do the same with a 20W mobile RTX and a better performing antenna (theoretically).

So after all I will keep this antenna and enjoy mobile HAMming. But I had to modify it to suit my needs and safety requirements.



Now I do want to check the SWR.

12 July 2018

My Nagoya UT-106 review

I needed a small VHF-UHF antenna for mobile operation. I use mostly UHF, so I picked one of the cheapest antennas on the Bay with the idea of using the connector, coax, magmount while cutting the antenna to a simple 430 MHz 1/4 wave vertical.

I ordered a Nagoya UT-106.

In the past I owned a similar dualband antenna, but with just one coil, so I can do comparisons. The very first impression is that the base is too small. The  UT-106 base is as large as 2€ coin and purely circular, while the older was slightly larger and had three small protruding feet that helped stability.

A smaller base means a smaller metallic area that couples with the car body (reflector or ground plane). Also the antenna oscillation is more likely to snap everything off the car in a bump or just at highway speed.

So I tried the magnet on pure iron. Weak. Too weak. Wobbling the antenna radiator caused the whole base to jump back and forth. I will not mount this antenna on my new-ish car and drive around!

As last check I tried to lift the bottom cover that is not made of rubber. It was not hard at all as it pulled off with my thumb and no force whatsoever. The result is visible in the picture below. Horror! The magnet is sticked to the paper base and not to the conic shape! So the antenna could fly away and leave you with a black sticky paper magnetically attached to your car! Actually there are sign of glue on the base side, but the adhesive paper won!

With all these "bugs" I will not even try it on-the-air.

I know the old say "you get what you pay for". I was prepared to do some improvements, but this is probably too much to fix.

My review: don't buy it.

27 June 2018

Data for obsolete HP 1820 ICs

You will read everywhere that in the golden age of electronics (1960's 1970's) many parts were very short lived because newer versions became available almost each month.

This means that if you are reverse-engineering a board from those years you might meet strange part numbers that do not have modern equivalent. The problem arises if there is no manual/diagram available or you have a board of unknown origin.

Today I will concentrate on HP integrated circuits from 1970 and thereabout. Just because the HP 9403B device is full of them. They were numbered 1820-.... with no resemblance to the current CMOS or TLL naming standard.

I realised that the information is available online but it is not indexed because it is contained into PDF scans of device manuals, that in those years were written in a very detailed way: they would explain in detail how it worked theoretically and practically, schematic diagram included.

So searching for the part number will not get you far. Hoping to help the community of reverse engineers and addicted to 1970 circuits, I include below the pinout of some HP 1820 integrated circuits with plain text description found in the HP 5326B manual, so that it should become indexed by search engines. Please leave a comment if you found the information you were looking for.

List of integrated circuits currently covered:
HP 1820-0054
HP 1820-0068
HP 1820-0092
HP 1820-0094
HP 1820-0102
HP 1820-0117
HP 1820-0142
HP 1820-0145
HP 1820-0147
HP 1820-0174
HP 1820-0198
HP 1820-0199
HP 1820-0201
HP 1820-0209
HP 1820-0212
HP 1820-0213
HP 1820-0223
HP 1820-0238
HP 1820-0253
HP 1820-0272
HP 1820-0273
HP 1820-0274
HP 1820-0275
HP 1820-0276
HP 1820-0729 (see 1820-0092)
HP 1820-0307
HP 1820-0327
HP 1820-0328
HP 1820-0558
HP 1820-0561
HP 1858-0004

There is one image file per part number. The file name is the part number.

The zip file can be downloaded here http://bit.ly/HP1820pinouts on Google Drive or here http://bit.ly/HP1820pinoutsDropbox via Dropbox (1.1 MB).




26 June 2018

HP Nixie driver IC (HP 1820-0729)

The HP 9403A brought another set of Nixie driver chain ICs in my home. It was the HP take on the matter: custom ICs with hard to find pinouts, let alone a datasheet. Apparently with one positive side: the pinout was laid out to simplify PCB routing.

I found an HP 1820-0729 that is an updated version of HP 1820-0092. They are a sort of 74141/7441 BCD to decimal decoder and driver but obviously with different pinout.

Ahead of that there is an HP 1820-0116 that is a 4-bit latch.

HP 09403-60006 board with buffer, driver and Nixies.

I have got an idea where to look for pinouts, but it is another story.




21 June 2018

A cheap hands-free solution: first test

Just a quick update on the hands-free solution.

The stock earpiece-microphone of the Baofeng UV-82 is quite lousy with its muffled sound and insensitive microphone. At least that's how my specimen behaves. So it is not a big deal to sacrifice it.

I removed the microphone capsule and used it to feed the audio coming out of the wireless receiver. I added a 470nF capacitor in series to block DC. Initially I chose 10nF but the resulting signal was too low (checked on the oscilloscope). Also remember that this C makes a high-pass network together with the input Resistance, so your voice could be attenuated further.

The first on-air test resulted in low audio. Then I hit twice the [+] button on the transmitter and the transmitted volume was back to normal. An unknowing HAM did not report a different sound of my voice, so the whole thing works.
VOX can work but it is insensitive and on UV-82 there is no setting for the hold time.

Next step will be to build everything into a comfortable box, add a lever PTT and possibly a way to power up the receiver together with the RTX. It has to work until I don't receive the external antenna and check if it can handle the RF power of the mobile transceiver I still own.

19 June 2018

A cheap hands-free solution: the idea

One of the many drawbacks of driving and talking on the radio is that the microphone is usually physically wired to the transceiver. Let alone that it is illegal in many parts of the world. Very few RTX's have a hands-free solution out-of-the-box and even in 2018 too few support some form of [Bluetooth] detached earphone-microphone. Last but not least, all off-the-shelf solutions can be expensive.

Obviously I looked for a DIY alternative. To simplify things a bit I assumed that an RTX for mobile use has enough audio power in the speaker so that an earphone or an audio amplifier is not needed. This means we need to transmit audio one-way only: from the mouth to the TX.

Now our feared Chinese fellows come very handy. Head to any of their portal and look for "Wireless microphone 2.4 GHz" (they have some that operate in UHF too). Be prepared to dig through many products until you land on something advertised for touristic guides. These products have a boom mic with transmitter and a simple receiver that is supposed to plug into an amplified speaker or other form of audio amplification.

I bought the product from NEWGOOD for 19€ (in 2017). It's still a bit more expensive that my desiderata since I hoped for 10-12€, but definitely cheaper than other solutions.


Both parts have an on-off switch, a microUSB socket for charging and the transmitter has volume control buttons. They are not Bluetooth so there's no need of pairing. I have no idea whether two similar units would interfere or could be swapped, but it's not a popular product I'd say and the risk is low even if the advertised range is 50 metres!

In its intended use, so with an amplified speaker on the other side, it works right. The audio quality is also very good.
How to interface with the transceiver then? Just feed the receiver output into the microphone input through a bypass capacitor, think of a way to handle the PTT: pushbutton, lever switch, VOX, .... and hope that signal levels & impedances match!

My current mobile RTX is the Baofeng UV-82 handheld, so it will be my test platform.

14 June 2018

HP 9403A System Control Panel

The purchase at Friedrichshafen 2018 with the best €/kg was the HP 9403A device. And I think it will have a very high fun/€ ratio too!

Let's see how it looks:

HP 9403A in FN, near the beer kiosk.
There are three display windows, a numerical keypad, other buttons, flip switches and a key operated switch. Let's not forget the two handles for carrying. On the back side there are three large barrel connectors with a high count of contacts (40 or so), AC power, fuse, power switch.

Me and the HP 9403A.
A preliminary search on the Net before the purchase did not return meaningful data. It turns out HP has "recycled" the 9403 code with inkjet printer cartridge. The challenge is set!

The seller held the device until the afternoon, when I picked it up on the way to Hall A (with new stuff) and the car.

I had to be careful not to hit someone's legs with it. I took few breaks along the way and I even sat on it. Hans G0UPL wanted to get one too because it had Nixies and all the driving circuitry. Yeah, I know, that's why I got it in the first place.

So the mysterious device came home with me, silently opening a deep dive into 1970's documentation.