Friday, 25 December 2015

Repaired my ATU

Merry Christmas!

Not wishing to contend with an evening of dire XYL style Christmas TV (Strictly Come Dancing, Call the Midwife and Downton Abbey) I escaped into the shack and decided to repair my Vectronics VC300DLP Antenna Tuner. I got this ATU second hand last year and while it has been serviceable it had become temperamental of late. The units rotary inductor switch had become stiff and suddenly I was unable to match the OCFD on some bands so it had clearly broken.

I had a 12-position switch (rated at 5A) and knob, originally sourced for an abandoned project and hoped it would be suitable. The existing switch knob on the ATU wasn't an original, I'd assumed it had replaced one lost or broken. When I removed the cover it was clear that the whole switch had already been changed at sometime.

I also noticed a prominent burn mark inside the inductor coil, caused by a clear break in the insulation of the wire which was resting on the grounded bottom plate.

I know the previous owner of the ATU has a 300W RM BLA-350 linear amplifier, whereas I only normally operate around 30W maximum at my QTH, so not sure how much of this arcing I had caused but it needed sorting! A little over half an hour with the soldering iron and I had replaced the switch and slipped some heat shrink over the broken insulation and re-soldered the wire, lifting it off the ground plate.

The ATU seems to work well, now fitted with a new knob (just missing a cap at the moment) the switch turns nicely. I also cleaned up the SO-239 connectors on the back as they were tarnished and oxidised. I used a small bit of contact cleaner on some cotton buds to clean up the threads and the centre pins, removing a surprising amount of crud. The patch and antenna leads now screws on much better.

With the Mother--in-law staying with us over the festive period I suspect I may be in the shack quite a bit, I have plenty of jobs and half finished projects to keep me busy!

Tuesday, 22 December 2015

DMR - Joining the Dark Side!

As a birthday present to myself I have just ordered a Retevis RT3 DMR hand-held off eBay which should be delivered just after Christmas.

South Kesteven ARS had a talk in October by Sean Burton 2E0ENN about amateur DMR where he demonstrated some handsets and the new DV4Mini which allows gateway and internet linking for the various networks, DSTAR, DMR and System Fusion. This piqued my interest in the DMR scene.

As I posted last time I dabbled a few years ago with decoding PMR DMR using software and a sound card but they were very hit and miss at the time. I reacquainted myself with the various projects and using the FUNCube Dongle Pro+ and the latest version of DSDPlus (support forum at monitored the nearby GB7RR DMRPlus repeater managing to get some reasonably clear decodes of some amateur transmissions.

I decided to dig out my Realistic PRO-2022 scanner and using a discriminator tap fed into the sound card got slightly better quality decodes.

Doing some research and reading a couple of reviews had decided I was going to get a Tytera TYT MD-380 when funds allowed but spotted the Retevis RT3 which appears to be identical and slightly cheaper.

I know some people wince at the thought of DMR and issues with proprietary technology used in some of the systems but I think the genie is out the bottle and it isn't going away soon. Adoption of DMR appears to be growing with talk of restructuring of talk groups needed to deal with the growth (whatever that means!) so I should at least get my feet wet and understand the technology.

I registered for an ID, now off to decode the jingo and understand all this talk of codeplugs, talk groups and time slots.