AR8600 Filters and Add-on.

As mentioned earlier, the AR8600 receiver originally has a poor SSB filter. 

I do have an old Mk1 and a newer Mk2, and the filters are different. Also, the Mk1 stops at 2040MHz, and the Mk2 continues up to 3GHz, so it is useful for reception on 2400MHz, too. 

I suspect that a preamplifier will be needed for those high frequencies. I can find one, or use a module I have for that.

I made a search on Ebay after looking at a video on updating the receiver.

I did locate one SSB filter suitable filter, and ordered it from Japan. This is an 8-pole Collins SSB filter that should be much better that the original Murata filter in the receiver. The post mentions the AR8600, so I hope that the filter fits in the PCB. I am hoping to receive the filter some time in February.

The filter I ordered looks like a fit for the Mk2, and that suits me fine, as the Mk2 has the wider frequency range.

I suspect that I will have to find an alignment procedure for the AR8600s, as there seems to be some misalignment, at least in the Mk1 I have used until now.

I do have an AR7030, too, and I also ordered a 500Hz CW filter suitable for that one.

When I look into my crystal ball I see some upgrade activity in my future ;)

An added Idea Box entry:

The other part is the audio output of the AR8600. The built-in speaker is very small and not very loud. So I am thinking (ouch! ;) ) of building myself a new audio device with an external audio amplifier, possibly with an equalizer circuit (I have PCB a module for that), and an audio CW filter.

I do have a stereo amplifier suitable for use with at least two radios. With a little mixing trickery that could easily become 3 radios simultaneously, one in the left channel one in the right, and the last one in the middle. With an external switch box (that I already have) more radios could be added to the external audio system, albeit not all radios simultaneously.

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.

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.

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.

Mini Project #1.

Before the NanoVNAs became widely available it was tricky to find low cost test equipment for testing SWR or return loss in the low GHz range. 

At the time I did find one possibility: The transverter-store in Ukraine sold some low cost impedance bridge PCBs, so I got myself one.

The PCB bridge circuitry looks like this:

Looking at a Youtube video I found that the PCB has a fault. The bridge has 2 50Ohm resistances, made up by two 50Ohm resistors that should be connected in parallel. On the PCB he tested, and on mine, this is not the case. No connection between 2x two islands on one side of each pair.

Now, this is not difficult to correct. A short piece of wire  mounted at the junctions between the resistor pairs solve this.

A quick test using my NanoVNA 2 showed a shortcoming of the NanoVNA output level (too low), but also gave an indication of the functioning of the bridge.

With a 6dB attenuator as the DUT (Device Under Test) the return loss showed close to 12dB, as it should.

Testing a 10dB attenuator the same way showed that the return loss went down into the noise of the NanoVNA. Close enough to 20dB, so I accept the reading as correct, and that the bridge is working properly.

That is the end of mini project #1 of this year.

Will I use this bridge a lot? Not really, but I did want it to be in working order. It is now going into the test PCB pile as a working unit.

The NanoVNAs that came out after this are much easier yo use, and much more versatile. The cost is not prohibitive, so in the lab I will be using a NanoVNA F (I think is the designation) for frequencies up to 1GHz, and a NanoVNA v2 for up to 4GHz.

Mini Projects for This Year.

I have an idea for an addition to the challenge/wish list for 2023.

In my shack, and in the lab there are a ton of small projects that will improve the ability to make larger projects. 

This could be an extremely simple repair or modification of some existing equipment or a PCB module.

The intention is to make a small blog entry for each of mini projects.

There should be one mini project per month as an average, so 12 of them this year.

Why?

Sometimes I get the impression that I do not doo anything, even when I do. So this is to show me that I do, in actual fact do some stuff, even if not as much as I want to do.

This is, of course in addition to doing a few larger projects.

Last year's large project was making a minimum of 365 QSOs with 5W output, so I suspect this year I will make fewer QSOs, as I have some practical building projects I want to get done.

Let us see how that goes.

One 10m Antenna With Multiple Receivers.

Some time ago I made a modification to my IC-703. It was a RX antenna adapter, originally made for the IC-7300.
It was possible to fit it into the IC-703, albeit with a bit of extra work: I had to file a bit of the adapter's plates an a bit in the radio casing, but it looks acceptable to me.
For a while I only had it connected to loop back the receiver signal, but this week I connected a signal splitter, so it is possible to connect more receivers in a way that does not destroy the receivers when I transmit with the radio.
Yes, when I transmit, I cannot receive anything on the 10m antenna, but I consider that an acceptable compromise. Further, it is possible to use a more complex system, so a transverter could be connected to the transceiver, too.
A TX power amplifier I have, I can connect it to the RX part/common connector, so I can transmit up to 200-250W with that combination

This is how the system looks right now:

10m vertical --- IC-703 ---                               !--- IC-703 RX input
                                         !                             !
                                         !                             !--- RX monitoring 28.074 (FT8)
                                         --- Signal Splitter --
                                                                       !
                                                                       !--- RX monitoring the international beacon project
                                                                             on 28.200

The splitter has more outputs
At the moment the signal splitter is just hanging next to the TRX, but it is the intention to build a casing for the system, so a preamplifier (attenuation in the splitter is too high for some of my receivers) and a switch for transverter or separate RX antenna can be added. For now, the system just has to work as it is, as well as possible. Improvements can come later, after other projects have been done, at least in part.

I would like to have a similar system for the higher bands (6-4-2m and 70cm), but that will have to wait.

IC-703 Modification.

For the first time in almost 2 years I have been traveling (more than about 100km from my home) for a bit less than 2 weeks, and I am back now. This was a non-radio-related round trip From my home near Copenhagen through Northern Germany, The Netherlands and Belgium, then to Paris. On the way back via Köln (Cologne). Last year I spent getting rid of a colon cancer, and I am now free of it, just going to control visits every few months.

Today I modified my old IC-703 for receive output/input. Will likely use that TRX for 10m with aux RXs for 10/11/12m propagation monitoring, using the TRX with the 10m PA running about 200 - 250W CW or about 150W FT8. Should work nicely.

Why do a modification like that ?
Well I wanted to be able to add some kind of spectrum/waterfall display, and possibly use the same antenna with several monitor receivers, e.g. beacon watch, FT8 watch etc.

I was using a kit purchased for doing the trick on a IC-7300, but decided to try it with this one first.

The mod took a bit of filing off the outward side of the new adapter and filing a bit of the bottom cover, and removing the connector for the external ATU control. The external control is not necessary as long as the built-in tuner works (or is not needed at all).

It now fits nicely into the casing.

System check of the RX shows that it is working nicely in through-mode.

It is likely that the modulation circuit will need an equalizer, because the reports on the modulation are not good enough. Initially, I will check the adjustment of BFO and SSB filters.

Second use for this low power TRX could be driving a transverter to 4m, including RX output for AUX RXs, such as spectrum waterfall.