2023-01-26

Mini Project #4a: 16 element Flexa Yagi for 23cm.

A while ago I purchased a front-mast mounted yagi antenna for 23cm.

This is a 16 element yagi with a  stated gain of 14dBd. We shall see, but it is much better than no antenna at all ;)

Today I got that one assembled.

Next: a corresponding 70cm antenna for front mast mounting.


2023-01-23

Mini Project #4. 4 El. Yagi For 2m.

 A while ago I purchased the Flexa Yagi 4 element antenna for 2m. 

At the time I purchased it I did not have sufficient strength in the fingers, and  the precision to do the job, due to having chemo therapy. That is now much less of a problem, though there are some side effects of that left over. Yes, I did not ask for assistance, as I like to do most of my stuff myself.

This one is designed for being mounted in front of the mast, so the mast would be behind the reflector. This allows the antenna to be mounted for horizontal or in the vertical polarization.

Another advantage is that this antenna has very thin steel elements, so only the boom is clearly visible from the ground. This is part of my low-visibility antenna system.

For my use I have mounted the mast clamp between the reflector and the feed element.

The FX 205V has a claimed gain of 7.6dBd. That may be a bit on the high side, but let us estimate the gain to be above 6dBd, and I will be satisfied.

I have used a "Big Wheel" or "Clover leaf" omnidirectional antenna for a while. It has been mounted right in the to of an apple tree, and I did make a bit of DX on 2m with that one. Ukraine was one of them.

In order to get the full benefit of this antenna I need to mount it on a rotator. That will not happen until the weather is much better, some time in the spring. When that happens, the small Yagi will likely be mounted 2-3m higher than the clover leaf antenna, and due to the height difference and the fact that the Yagi will be in the clear, I would expect signals to improve significantly on 2m, probably in the order of 10dB.

What next?

Maybe the 23cm Flexa Yagi I have had lying in the box for quite a while Then it will be ready, even if I cannot mount it yet.

2023-01-22

PM2B and Documentation, Mini Project #3 Goes on Hold.

Having seen the receiver working, if not very sensitive, and the transmitter part with no output at all,

I am putting the mini project on hold.

First of all because I have no proper documentation, no service manual, no circuit diagram and not even a user manual. If the set would have been in proper working order I would have found out how to use it, no problem.

Second, the transceiver is so old and primitive that I find the operation too cumbersome to my kind of CW operation:

1) The receiver preselector has to be readjusted when tuning through the band, and especially if changing band.

2) The transmitter needs 2 extra adjustments after tuning over the band, or at band switching.

3) The VFO tuning ranges are too large for my use. For CW I use about 100kHz at the bottom of each band. This model covers 3.5-4.0 MHz, 7.0-7.4 MHz and 14.0-14.8MHz. On 20m the useful tuning range of 100kHz takes up very little space on the dial.

4) I have not found any way of making an offset between receive and transmit frequencies, meaning that tuning to a proper receive tone offsets the transmitter frequency. Not practical on crowded bands. Modification necessary for this alone.

5) The audio output can only drive high impedance headphones (>1kOhm). Not very practical, as I do not have those any more, though I could use a piezoelectric earphone for tests, but I would not use it regularly. In order to use the set with ordinary modern headphones or earphones, or a speaker an additional audio amplifier is necessary. This already means that  another modification is needed in any case.

For these reasons I do not find the time to restore this radio to its original state a good use of my time.

So what to do now?

Modifications are needed in any case, if I should want to use the transceiver

The casing, with some shielding at the sides will still be useful. I can build my (partly) own construction in there, and make myself a multiband CW transceiver. This is no longer a mini project, but a much larger one.

I may try to find a replacement for the PA transistor, maybe the driver if necessary, so the transmitter can be shown as operational, but that is all. Apart from that, the PM2B mini project is on hold.

I do not have any lack of mini- or smaller projects, so life goes on.


2023-01-20

Mini(?) Project #3. Ten-Tec PM2B.

After finishing the IC910 mod, here is the next mini project. This may be more than just a small one.

For a very low price I purchased two low pass filters (30MHz) and a non-tested Ten-Tec PM2B, so I do expect to have some activity before it is fully functional.

This is an old CW only QRP transceiver, officially with 1 or 2W out, and with a direct conversion receiver. The rig covers the 80, 40 and 20m bands

After cleaning the AF potentiometer and some slide switches I got it to draw about 30mA from a 14V power supply. The headphone output showed some noise, variable with the pot. It looks like the headphone output is high impedance. It does use banana plugs, not even a mini jack connector. Yes, this is very old.

With an external SSB receiver I found that the local oscillator is working and can be tuned correctly.

No external signal received yet.

No transmit output detected.

Also I have no documentation, not even a circuit diagram

It does indeed look like there is more work to do with this one

Looking into the casing I was not impressed with the build quality, with long flimsy wires running around, and it looks like it has been messed up somewhat.

This might end up being a larger project, essentially building a modernized version of a direct conversion CW transceiver with a digital VFO, and maybe with additional bands. We shall see what I do with this one.

If I do a total make-over I may add some shielding to the sides of the transceiver, as they are totally non-shielded.

Mini Project #2 (IC910) finished.

 The addition of the 23cm band to the IC910 is now complete.

After disassembling, checking the (flat) cables etc the fault was still there.

A complete reset of the CPU, losing all memory channels, cured the problem. The radio has been running all evening without trouble.

This concludes mini project #2.

I still need to set up an antenna or two for 23cm, but that is for later.

2023-01-18

Quick Update. Mini Project #2a. IC910

Messing around inside the IC910 did get me improvements, but it developed a fault.

When setting a frequency, after a short while the dial moves the frequency without any action.

Initially I suspected that the switches in the microphone had got faulty, but this happens even with the microphone disconnected.

Then there are two more obvious possibilities:

a) Dust has entered into the the rotary encoder, or

b) A flat cable has a poor connection.

So tomorrow the radio goes on the lab desk again, let us see if we can get rid of that annoying fault.

Yes, beware when you mess around inside an older radio.

2023-01-17

MIni-project #2: 23cm etc on the IC910.

 The second mini-project of the year is almost complete.

Two things had to happen with the IC-910: 

1) The original reference oscillator needed to be replaced with a high-stability oscillator. This was necessary, because temperature drift cannot keep the IC910 on frequency, especially when operating at high power levels.

I got the new oscillator mounted on the PLL board, and then the adjustment started. Initially I adjusted the output signal while transmitting low power FM on 70cm. Yes using lots of attenuation. I was using my microwave capable spectrum analyzer with a 10MHz GPSDO as reference. The trimmer in the oscillator was a bit fiddly to work with, but I got the initial 70cm frequency adjusted within 150Hz of the set frequency. After some warm up it looked a bit better.

Time to mount the shield for the PLL and the 23cm module. This is a rather easy add-on.

Set the main band to 23cm and test on 1296.000MHz. The frequency was less than 250Hz, and after warm-up it was within about 150Hz.

Now the radio is re-assembled with all the covers, and tomorrow I will make another test of frequencies with the radio fully assembled, and after a good warm-up period.

I do not expect any significant change, but I do need to check, so I know the offset.