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Friday, 25 May 2018

Tuning an ICOM


I've been fiddling lately with external ATUs and most recently the linear I mentioned last time.

More and more I keep wanting an easy way to generate a tune carrier from the IC-7610. Now, when Kenwood designed the TS-990 (the best radio in the world) they got everything right. There is a tune function you can allocate to one of the user programmable buttons, and also you can set the tune power by band - what could be simpler?

Well, with the latest and greatest Icom radio, you have to stick the radio in FM or AM or RTTY, press the Transmit button after adjusting the power to the required level and sticking a chicken down your trousers and facing north. The last bit isn't actually necessary, I was just checking you were paying attention.

So here we have the answer to the problem:

The switch in the middle of the schematic selects the internal or external ATU and the outside switch (in my case a push button) enables the carrier:

The whole thing connects to the external tuner connector on the back of the majority of Icom radios, which I've made a plug for by butchering an old PC PSU connector:

Easy, don't you think?

Thursday, 24 May 2018

Splashing Out Somewhat


I decided to get myself a new toy. The idea is that this replaces the linear amp, the antenna switching, the radio switching on HF plus the ATU - all in one box. Also it doesn't need to "warm up" or tuning on each band.

So I brought it home, somewhat excited:

Now, I first tried it with my TS-990 as the exciter. The manual doesn't actually tell me anything about required drive levels, but anything from the TS-990 generates "INPUT OVERLOAD" error - even only with 5W output. So more consultation of the manual and it seems they are keen on you using ALC connections to control the exciter drive levels, so I hook up the ALC line and then this is what happens:

Now that's really quite strange.

Next I try the IC-7610, connect up the ALC and PTT lines and it seems to work OK, however, I have very little control over the RF out - in fact I cant get the amplifier to deliver less than just over 500W output even on the lowest power output setting. That's not very clever - I want to be able to control the RF and gain of the amplifier.

So, some email back and forth to the manufacturer and it seems there are two versions of this amp. One for the US market which includes an attenuator in the drive line so that 25-30W of RF is required for full output, and an EU version without the attenuator.

SPE sent me this table which shows the input RF needed for full output by band and power setting (you can have the amp on Low, Med, High):

So at this point I fell off my chair! This amp eneds only 2W of drive on the low bands for maximum output. The only way that low level of drive is possible with most modern transcievers is by using the ALC all the time to restrict the output of the rig - which is exactly how this amp is "designed" to operate. I think the issue with the TS-990 is that despite ramping the ALC voltage to the most -ve it can, the output is still too high to drive the linear.

Either way, there is no way you can set the controls to deliver, say, 200W output. You can have maximum bananas (which seems to be 500W, 1Kw and 1.3Kw) depending on the Low, Med or High selection of the amp power switch.

The manufacturer recommends you run your rig at FULL RF output and rely 100% on the ALC circuitry to protect the MOSFET in the linear from being fried. I personally don't like this theory at all.

Needless to say the amplifier has been returned today for modification to the USA version so I have some hope of controlling the RF output.

Here you see the drive level of 3W:

which produces 508W out in the "low" power setting:

Bonkers, don't you think?

Monday, 21 May 2018



I'm forever adding bits to projects after they are complete. The recent PTT Switching box I made back here is no exception.

Since the original design I've added/changed a few things:

  1. I've significantly sped up the sequencer;
  2. I've added automatic relay switching for the DRV and RX antenna connections to the TS-990. This means that the transverter RF connections are automatically selected when the band select switch is on 2M or 4M. There's even a delay to the relay activation so that passing the switch through that position doesn't falsely change things over;
  3. I've included all the external switching into the schematic as best I can

So there are 4 external PTT connections - these are the triggers to the sequencer and are selected as Radio 1 - Radio 4.

Associated with each Radio PTT input is an ALC output back to the radio so that the selected radio does not generate any RF until the sequencing is complete.

There are PTT outputs to the 3 amplifiers; HF, 2M and 4/6M - these are only keyed when the band switch is in the appropriate place.

There are PTT outputs to both by transverters. Ditto for the amplifiers, these are only keyed when the Band Select is in the appropriate place.

The full schematic is:

and also in a higher res PDF here.

This is our very beautiful Bonnie Dog; in our local dialect her facial expression is translated as "thank God it's spring".

Local conditions.

Thursday, 17 May 2018

DB0XY on 432.475


Some interesting propagation on 70cm this AM:

Fun, egh?

Friday, 11 May 2018

PTT Revisited


This all started when my 2M masthead preamp from here failed. This can only be because there has been some RF into the device, as everything else int he preamp looks fine.

So, how can this have happened?

On 2M, the preamp is powered via the coax and all this is taken care of by my Beko Amplifier.

So to add some more "belt and braces" protection to this I decided to re-visit the PTT switching arrangement I created way back here. Now I've learnt a lot since then and have built a few sequencers now, so the ideal solution seems to be to keep the same switching concept, scrap all the relays and use a sequencer. I also decided to add an ALC output to each radio so I can keep RF at bay from source until the very last sequence event has occurred.

Here's the design I came up with:

I've uploaded a PDF of the schematic here.

This copies a number of previous sequencer ideas but now also adds a ALC -ve voltage output that I can switch to the appropriate radio with a front panel selection.

U1D is configured as an oscillator which is then -ve rectified by D6 and D7 and then switched on and off by the sequencer using U3.

Here's the finished build just about to go into test:

You can see that I have also used some co-ax relays (the latching type) and the drivers we finalised here to switch the DRV and RX Ant connections between my 2M and 4M transverters. The box also has a radio select switch (1-4) and also a second selector for HF, 6M, 4M and 2M.

The second switch operates the HF linear only in the HF setting, the 6/4M linear only in the 6M setting, the 6/4M linear and the 4M transverter in the 4M setting and finally the 2M linear and the 2M transverter in the 2M setting.

I just need some feet and some knobs!

**UPDATE** Some more info on this project here.

Saturday, 5 May 2018

3cm Learning


Ween up a big hill today to play on 3cm:

Pretty nice day in my bit of England:

Here's a video of the Finningley beacon as RX today:

Here's what I learned today:

  1. The beam heading on the dish is extremely sharp;
  2. I need a more accurate way to determine beam headings;
  3. I need a way to turn the mast whilst also tuning round on the radio;
  4. The fitting of the mast into the base is a bit loose; the pole isn't completely vertical
All in all, 3/10 could do better. But I have made QSOs now on 10GHz and that feels like a great achievement.


Here's Miss Pepper, assisting as per usual: