13 September 2018

Rethinking my mobile setup

Alright, the shortened UHF-only Nagoya UT-106 is back in service.

I added a piece of RG-58 with PL-259 so that I could measure SWR. But just the fact of terminating the coax with a PL-259 made me think of a way to fit the QYT KT-8900 mobile in the new car in place of a handheld.

While the large glass roof drastically reduces the flat metallic area for a magmount antenna, it does not block RF either. Since the only place for a small magmount is above driver's head, the antenna cable would be in the way of the passenger because I don't leave the antenna outside when the car is unattended, go figure. But there is plenty of space in the back of the car. Yes, inside, but with all those transparencies (be it glass or plastic), RF-wise it is almost like being outside.

The plan is to place the magmount base on a metallic surface and let it rest on the parcel shelf. At home I found an L-shaped 40 cm long iron piece that can be forced between the back seat and the shelf. SWR of this combo is 1.5:1 on the FT-817. So far so good.

Will it work?

06 September 2018

Nagoya UT-106 intermittent signal

Now that I was enjoying trouble-free mobile HAMming, my modified Nagoya UT-106 developed a fault causing intermittent reception. Moving the coax near the RTX would restore/loose the signal, so probably something has broken in the coax. Since the handheld lays on the passenger's seat, holding the microphone causes it to move around and put some stress on the cable.

I will cut out the broken part and try to resolder the SMA connector. Before that I will fit a PL-259 so that I can try the whole setup with a more powerful RTX as well as measure SWR.

03 September 2018

FM radio for the morning routine: September 2018 attempt

Following my previous post on two attempts at joining the morning news and the morning bathroom routine, in both cases something is too wrong. Memory lost and instable signal are no-go.

Initially I admitted my failure to provide a suitable device and let the family member head to the shop to look for a replacement. Then an idea strike: why not use the FM radio into that old Samsung Galaxy S phone that was gathering dust? Just fit a 3.5mm jack (with enough wire) to behave as an antenna and set the output through the internal loudspeaker.

Bingo! While an overkill, it is battery powered, rechargeable and does not loose memory when the battery goes flat (but you can monitor it easily). It has more than enough audio power to fill the bathroom and costs nothing. Last but not least there is a self power-off setting at 30 minutes! The only drawback is that the RF-GSM part has to be ON to receive FM radio. But that works even without a SIM card inserted.

As shown in the picture, if the FM station is close/strong enough a 3.5mm jack alone acts as a perfect antenna (picture shows a 5mm to 3.5mm adapter). Probably it also helps not to overload the input stages resulting in better reception!

Let's see how long this solution lasts.

Note. I know I could have used an Android app to listen to the Internet streaming transmission. But who knows if there is still a working app around for Android 4.x? And how it would compare with power consumption? And the current over-the-air solution works even during power outages.

01 September 2018

FM radio for the morning routine

The "old-style" replacement RX-16F
I was appointed an apparently simple task from a family member: have an FM radio in the bathroom to listen to the morning news. It is basically a single frequency FM receiver outputting audio through a loudspeaker. Possibly as small as possible and requiring as little maintenance as possible. Something: "flip a switch and listen to the news."

If we were in the 1980's I would buy an analog tuned pocket radio powered with two AA batteries. Unfortunately they don't seem to be produced anymore, replaced with energy-hungry digitally tuned radios (with a varying degree of user friendliness user interface). Used devices have all sort of problems.

4 years ago I bought a small cube powered with a rechargeable Lithium cell (Kevler KP-520PLL). It would receive FM just fine with a big problem: current consumption. Even when powered off it would drain the battery flat in a week (2mA when off, 48mA when on). What is worse is that it looses memory of the last tuned station when the battery dies and the single-button tuning system makes it really annoying to reset way too often.

Then in Marzaglia ham flea market in May 2018 I picked a 1970's analog tuned FM radio that sounded good in the field, marked RX-16F. This one, while lasting forever on a couple of modern AA batteries, suffers a long forgotten (and solved) problem: the hand proximity effect! If you hold the receiver in your hand it would behave perfectly, but looses the tuning and strength (no AGC!) when left on the table. It's fine for listening to the football match while walking downtown, but not practical for the bathroom morning routine.

I need a better solution.

Back of the FM radio.
RX-16F circuit.



27 August 2018

Flea markets in Croatia

I think Croatia's population of 4.1 million does not justify the presence of thrift stores. In fact I could not locate one that would sell electronics and related items. The key to success in this case is to know the right name in the local language. That's how I discovered periodic flea markets: "sajam".

While I have always known of Hrelic market in Zagreb, and never managed to pay a visit because I am never there on Sunday morning, searching for "sajam" on an Internet search engine brought up other events.

Like in Sesvete (East of Zagreb) every Thursday morning. Or in Samobor (N-W of Zagreb) every Saturday morning. And in Split every Sunday morning.

All of them open quite early, so you can get there at 6-7 A.M. and be back to your usual business before anyone notices.

I could visit Sesvete sajam on 2018-08-23. No pictures, sorry. It is a mix of farmers' (wholesale, sort-of), textile and flea market. Given the holiday period my impression was that the flea area was not too crowded. Best to get there by car. Electronically speaking, there were few sellers with this kind of items including one stand full of 1980's radio receivers. As usual you need your usual luck and trained eye to spot something interesting. In Sesvete sajam there are stands serving warm food, so if your bargaining takes ages you can have lunch break as well.

If you know other periodic "sajam" around Croatia please leave a comment!

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.