Moving an old CB walkie-talkie to 29 MHz AM - Part 1

Hello there, after quite a long pause I write again on this blog to describe my recent experience of moving an old CB walkie-talkie to 29 MHz AM in the 10 meter band.
I had found a nice pair of Inno-Hit RT923 talkies for 15 euros, while visiting a junk dealer shop near home, looking for something cheap and unusual for my personal collection of useless things. They looked in a very good condition and I though that probably there were still working too.
In the next few days, I sold the better-looking one on an on-line auction site for 10 euros and I decided to try moving the remaining talkie on 10 meters, 29 MHz AM. Here below a couple of photographs of the "star" of this post.

The Inno-Hit is a 3 channels, 2 watts, crystal-controlled handheld CB transceiver. The receiver is a single-conversion superetherodyne with 455 kHz IF. The tx frequency and the local oscillator frequency in the rx are controlled by two different crystals. The LO crystal is of course 455 kHz below the actual rx frequency.
The same rig was sold with several brands and some differencies (mainly cosmetic); for example Royce 1-402, Brilliant BT-1232, Finetone TNC-203, MacDonald CE-420, Universum BSG-3271 and maybe others. All those rigs came from the mid '70s and had a very robust steel case, with a small opening door on the front to access the battery pack. Some of them had external connectors for an external antenna, earphone, power supply or battery charger. Usually they were sold with only one channel actually equipped with crystals (for CB channel 11).

The astonishing successes of my good friend Franco I5KAP on 10 meters AM, with even very old and simple QRP rigs, inspired me.

A visit to Franco (who live 10 km or so from my QTH) convinced me to go ahead with my plan. Franco was very kind and helped me in deciding which modifications would have made sense to try.
First decision, was to leave the transceiver as much as possible in its original box and appearance. Given the very limited space inside the case, the only sensible modifications to do were to add external connectors for the antenna and power supply (or external battery) and of course to buy a new pair of crystals (for the rx and tx oscillators) for the 29 MHz AM band.
The crystals were ordered to a factory here in the north of Italy (unfortunately, they costed about 25 euros each, including taxes and shipment). Then I bought for 2 euros each some schematic diagrams of the walkie-talkies I mentioned above (in particular, those which had the antenna and power supply connectors) and I proceeded with my work.
I identified the better points in the circuit were to connect the external antenna and power supply, I prepared the small removable plastic panel that was inserted on the right side of the case (like in photographs below) and quickly checked that all was OK, both mechanically and electrically.

Now it was simply a matter of setting a small measurement bench and do some tweaking on the tx path and the rx path to ensure that the talkie could work properly at the new frequency. This will be the subject of next post. Thank you for reading.

Panasonic RF-2200 test on MW

A video showing a quick scan of medium wave band in the evening with an old Panasonic RF-2200 receiver, before and after my restoration work on it.

Panasonic RF-2200 restoration adventures - Final

This is the last post (here the previous one) of a series about the restoration of my Panasonic RF-2200 vintage receiver. This is about the final cleanup of the radio. In one of posts I spoke about restoring proper behaviour of switches and potentiometers by using the renowned DeoxIT products from CAIG Labs. While these products proven to be very effective in my case, however I suspected I had used a bit too much of them for each device. So before re-mounting the case of the radio, I wanted to try to remove out any excess of DeoxIT from inside switches and potentiometers, by spraying a lot of compressed air into each device. Well, the amount of DeoxIT that came out from potentiometers were really in excess! It spread out over the main circuit board - without causing any damage, luckily - and I had to carefully remove it with compressed air, paper towel and some cotton swabs.
My recommendation is to use only the strictly necessary amount of DeoxIT (or similar product), especially if it is in the liquid form (the spray form usually contains a reduced grade of product, which easily evaporates together with solvents).
I already had cleaned up the front panel, back panel and the knobs in a soapy bath of warm water (see pictures below), using a soft brush for the panels and a toothbrush for the knobs.

Now I had only to re-mount the radio and proceed with renewing the black plastic of the case. I started with trying the Novus 3 Heavy Scratch Remover, but it did not a great job. I have found it too thick and a bit waxy, difficult to remove when it permeates the small wrinkles and scratches on the black case, causing it to look a bit milky and opaque, not that good really.
Then I tried to repair to my error with a normal, typical spray polisher for car dashboards. Boys, it did it! Faster, easier, cheaper and very effective: ideal for my needs. The results are in pictures below. Far from perfect, but good enough in my view.

That's all folks! I hope you have enjoyed your reading (thank you for that!) and may be you have found something useful for your own restoration project. These beatiful old ladies are well worth the effort.

Panasonic RF-2200 restoration adventures - Part 4

So here we go again. Since latest post of this series (you can find it here if you like), I managed to complete my restoration of Panasonic DR-22 (a.k.a. RF-2200BS).
In this post I will try to summarize what happened during the alignment work on the radio and to provide some suggestions that I learnt from this experience. It was quite a time-consuming activity for me, requiring care, patience and attention, because of both my limited experience in this task and the number of adjustment points on the main board of the radio.
Here below you can see the testbench, with the RF-2200, a simple digital oscilloscope and a good RF generator (I borrowed both the scope and the generator from a laboratory at my workplace). For most of the checks, the digital scope was connected to the speaker wires, where I had connected a 8 ohm, 7W resistor just to provide a safe load for the audio amplifier of the RF-2200.

The big coil made of red wire on the gyro antenna of RF-2200 in picture above, was used to transfer the RF signal from the generator to the receiver during MW alignment. I didn't try to open the gyro antenna to expose the internal ferrite rod and get a better match with the RF signal from the generator. I wanted to avoid any risk of damaging the gyro antenna itself, which is a vital part and one of reasons of the very good MW performance of RF-2200. For the same reason, I didn't performed the adjustment of the MW antenna coil, which is one of the steps of the MW RF alignment process.

For the alignment, I relied on the detailed step-by-step procedure described in the RF-2200 service manual (you can easily download a PDF copy of it from the web).
With the exception of a few cases, the procedure is fairly clear and simple to follow, but there are quite many steps to go through. Some of the checks require the front-panel controls (for example, the AFC/bandwidth selector) to be set in a specific way and I found it easy to forget this point, in the middle of a number of adjustment operations. When you see that adjusting a given coil ferrite core or trimmer capacitor does not produce visible changes on the signal level, I suggest to stop for a while and to carefully check that the setup for that specific procedure step is correct. It is happened sometimes to me that one front panel switch was not correctly set. More frequently than desired I also realized I was simply adjusting the wrong coil or capacitor...
Compared to what is suggested by the service manual, often I have had to raise both the signal level and the modulation depth (in particular, during AM tests) from my RF generator, in order to get a good signal reading on the oscilloscope. For higher SW bands (SW3, SW4, SW5, SW6), typically I needed to set at least 75% modulation depth. This could also be caused by the high level of RF noise in the lab (at my workplace) where I was performing my measures.
Sometimes I reduced the level of audio output (by the volume control) to avoid clipping of the signal in the audio amplifier, which made it not possible to look for the point of maximum amplitude during a given adjustment. In similar cases, however, first measure should be to reduce the output level and/or the modulation depth on the RF generator.

If possible, I suggest to use plastic screwdrivers to turn ferrite cores of coils and transformers and for trimmer capacitors. This allows for an easier adjustment, by removing the magnetic/capacitive effects of a metal screwdriver.
In some cases, a plastic screwdriver does not provide the required torque. In such cases, be extremely careful: using a metal screwdriver for adjusting coils and transformers exposes to a non negligible risk of damaging their magnetic cores, which I did actually with L2 and L3 coils of the FM section (luckily not heavily enough to put them out of work).
Adjustment of trimmer capacitors is very touchy. I needed to proceed very slowly and with very small increments of rotation angles in order to be able to identity the position for the maximum signal amplitude.

All in all, I'm pretty satisfied with the results of the alignment. Even if it has been quite a demanding task, I think it was definitely worth to do it. Now my RF-2200 works much, much better than when it came into my hands from eBay. In addition, I learnt a lot and I had a lot of fun while trying to bring it back to its better days.

Tecsun PL-660 vs Panasonic RF-2200

At the end of my Panasonic RF-2200 restoration adventures (more in a dedicated post soon), I wanted to perform a very quick and simple comparative test on medium wave with my brand new Tecsun PL-660. The result is documented in the short video here below:

Panasonic RF-2200 restoration adventures - Part 3

This post follows Part 2 on the same subject. As anticipated, I proceeded in the restoration project of my Panasonic DR-22 (also named the RF-2200BS) with trying to clean-up contacts of front-panel switches and potentiometers.

For this purpose I bought some products: a spray "dust remover" (compressed air) and a couple of well-known products from CAIG Laboratories: the DeoxIT D100 for switches and the DeoxIT Fader for potentiometes. Here below a picture of the toolkit, ready for use:

First step was to try to remove as much dust as possible from inside the case, the switches, the potentiometers and the tuning variable capacitor. Using a bottle of spray compressed air was quite appropriate for this operation, as illustrated by pictures below:

Next step was to use DeoxIT D100L cleaner to restore proper behaviour of contacts in front-panel switches. CAIG guidelines recommed to always wipe off excess of their products. However, wiping off excess is sometimes not possible, especially if the cleaner is applied into a semi-sealed part, like in my case. If this happens, CAIG recommend to just apply a small amount of their product into the part to be cleaned. Here is where the "small squeeze tube" type of applicator helps (compared to the more common spray type), as it allows providing small drops to the target device.

Final step was to apply the CAIG Fader F100L to the potentiometers, to restore and lubricate their internal contacts. Here again, the small squeeze tube applicator proven to be perfectly suitable for my needs:

Just after a single application of DeoxIT, I noticed a significant improvement in contact reliability of switches and in noise of potentiometers. Nevertheless, the 125 kHz marker switch will require a second application of DeoxIT, as it still works not perfect. I plan a second round for it just before re-assembling the unit in its case. Stay tuned for more RF-2200 restoration adventures.

Sulla tragedia del volo Germanwings

Non se ne può più di leggere pagine e pagine, interviste di "esperti" di ogni sorta, sproloqui politici, post nei blog e sui social network e chi più ne ha più ne metta sui particolari - possibilmente torbidi - della vita del co-pilota tedesco dello sfortunato volo Germanwings, precipitato nelle Alpi Francesi lo scorso 24 Marzo. A nemmeno una settimana dalla tragedia, nessuno spende più una parola per le vittime del disastro aereo (in tutto 150); le cui vite spezzate - che continueremo serenamente ad ignorare - sono state destinate da subito a confondersi in un semplice numero, divenuto ormai quasi un punteggio. Così come nessuno sembra provare un minimo di pietà per i familiari di Andreas Lubitz, sospettato di aver causato volontariamente l'incidente, divenuto rapidamente l'oggetto della morbosa attenzione dei media e del loro vasto pubblico, sempre avido di soluzioni semplici e di colpevoli da vivisezionare. Qui in Italia un quotidiano - se così lo si può chiamare - nei giorni scorsi ha avuto la brillante idea di titolare a tutta pagina "Schettinen", accomunando così in un'unica battuta di triste umorismo - uno sfottò che a qualcuno dev'essere parso geniale o almeno spiritoso - due tragedie recenti e le sofferenze che hanno causato in tante famiglie innocenti. Chapeau.