2m Station Progress

Three months ago, a nice, clean 2m Microset 200W amplifier was advertised on a Facebook ham radio page.  With lots of money to spend on the house and kids, I struck an agreement with the seller to pay for this non-essential amp over three months.

The new arrival, together with its tidily homebrewed cooling fans.

Yesterday, the amp duly arrived!  In as-new condition, this was a good £200 cheaper than a new model.

This is the first time I've ever used an amplifier, so there is a little learning to get to grips with - not least whether a 25A continuous PSU would be adequate to power it (it is).   In general, it will have no use other than when there is unusual DX available via tropo and/or Es.

One issue that is common to all these amps is a momentary spike in SWR when using RF to trigger the amp.

I was fortunate that Jim, GM4FVM, helped me with his experience, advising that a wired PTT to the amp is better, and avoids this problem.

In practice, with careful adjustment of the output, ALC and audio levels, it's possible to reduce the spike to about 1.5:1, and it only lasts for a fraction of a second.  Jim says that it's crucial not to have the amp's receive preamp turned on if using RF triggering, as the SWR spike will eventually destroy it.

I've now wired the PTT on the amp, and Jim's advice is sound: the SWR spike is completely eliminated.  If you have one of these amps, just connect the lower pin, labelled, confusingly, '-', to the rig's PTT line (if that socket on the rig is already occupied and you don't want to disrupt your existing system, then you can, for example, strip some of the connecting wire back, and attach your amp PTT wire there - solder or any form of clip is fine.  The other, '+' pin you connect to the rig's ground.  That's all there is to it.  

The 8-ele beaming east at sunrise.

Nevertheless, I did get the amp up and running, and managed three QSOs with very strong signal reports of around -04dB, on an evening when there was no particular 2m propagation.  This, with the antenna in its lowered, wind-safe position of just 2m above ground!  As the map below shows, the signal from my east-pointing 8-ele beam was getting to most parts of the UK.

The wider message here for newcomers is that, with a little application of wisdom and care, used equipment can provide you with years of enjoyment.  I have only once bought a new transceiver.  Almost every other piece of equipment I have is used, and never caused me any problems.

IC-746 - a problem that wasn't!

Well, my heart sank yesterday as I connected up to the 2m slimjim atop my roof and tried to send FT8 with the new ICOM IC-746.

Nothing happened!

I tried to work through everything, but got nowhere.  The data transmission works perfectly on all bands except 144MHz - the very band I'd bought the 746 for!  If I manually pressed 'Transmit' on the front panel, the data went out just fine.  So it seemed to be a TX-trigger issue of some sort.

I could find no help on the internet, and so resorted to asking for help from ICOM in the UK.

Outstanding help from Icom.

I've specifically written this blogpost to highlight to others the incredible fact that ICOM actually phoned me back within 30 minutes of sending an enquiry to their servicing team.  How many companies bother to answer at all these days, let alone so quickly?

A very friendly technician told me it was simply a case of having a different transmit trigger line for VHF (the so-called 'HSEND' for HF, and 'VSEND' for VHF). 

With just one simple, free support callback for a second-hand rig, ICOM have shown themselves to be a rig maker worth taking very seriously in my next new purchase.  Take note, other makers!

Three others who must be thanked for kindly helping me when they might reasonably have just turned their eyes skyward at another fool asking for assistance were:

• Technofix, providers of just about any data/CAT cable you can imagine

• Neil, owner of low noise data interfaces and accessories at ZLP Electronics

• Sam Hayward at UK ham radio outlet, Radioworld

UPDATE:

I eventually found some useful information online, courtesy of N5KBP, Marty Duplissey.  My colleague PE4BAS rightly says there is pinout information in the manual (p.72), but I wanted to triple-check I wouldn't get it all wrong and damage the rig.  One thing to remember is that, when looking at the pinout diagrams, you are looking at the socket as it appears at the rear of the rig, not the plug you are trying to wire!

Here's what N5KBP kindly submitted, which may help others in future (or help me remember when I do it again!)

'All the audio goes through ACC1 regardless of band. Pin 4 is audio from computer to radio, Pin 5 is audio from radio to computer, pin 2 is ground and pin 3 is ground to transmit on HF. On ACC2 the only pin you will use is pin 6 for VHF ground to transmit.  All you need to do is to wire pin 6 on ACC2 in parallel with pin 3 on ACC1.   On my setup I built the ACC1 8 pin connection then just ran a single wire from pin 3 on it out to pin 6 on a 7 pin din plug for the ACC2 to enable transmit for VHF.  Basically get it going on HF then add the wire to ACC2 to enable VHF transmit.'

It turns out that it's quite difficult to solder another wire onto pin 3.  You need very thin gauge wire, first of all.  I found it a bit easier, although not ideal, to cut into the cable some way from the DIN connector, and take a tap from it.  Having not yet received my 7-pin DIN plug from E-bay, I couldn't wait and just fashioned a 'pin' from 1mm copper wire.

It got me going.  I replaced the wire with a proper DIN plug later.

This is my schematic for the connections:

Et, voila!  Works a dream!

First 24hr reception reports, with a fair few QSOs, too!