Radio Active

Radio Active

About the Blog

This blog is an occasional 'diary' of my radio activity, what I have been up to, any interesting stations I have heard, experiments carried out and my thoughts on band conditions etc.

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Please Note: The 'RSS Subscribe' button does not operate correctly with the Google 'Chrome' browser.

It works fine with Internet Explorer 8 (and probably other versions too) and also Firefox. I haven't tested it with any other browser, but if it doesn't work on your browser, try one of those mentioned.

Today on JT65a

Digimode happeningsPosted by Sean Gilbert Mon, August 02, 2010 19:05:23
Quite an interesting day on 20m JT65. Best DX has been V31UB in Belize, and at -7dB was quite strong. Another good one was DS1DLS from Korea. I've heard him a few times now, ZS1LS from South Africa was also logged once again. The West Coast of the USA is coming in now (1845UTC) in the form of N6MZ from Washington State (which is in '7' land, rather than '6' - it gets confusing when USA stations move states and keep the same call!).

It's a pity there isn't more JT65 activity on bands other than 20m, it's a great mode even if it's pretty limited as far as QSO content goes. I quite often put out a call on 17m just in case!

I may well try 30 or 40m later on, so keep your ears open for G4UCJ :)

73, Sean

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tuning the OCF

AntennasPosted by Sean Gilbert Sun, August 01, 2010 12:00:33
Last weekend, just before the IOTA contest I decided to try and tune my OCF/Windom so that it resonated on at least some of the ham bands.

The OCF started life at 10.5m long, I then extended it to 21m so that I would get better coverage of 40 and 30m. However I discovered that it was not resonating where I wanted it (6300kHz gave the best SWR).

The way I tuned it was not scientific, and I don't have access to an antenna analyser so I used the SWR meter that is built in to the IC756pro. Probably not the most accurate but good enough for my needs.

Anyway I started trimming the OCF, 6 inches at a time. After each cut I came into the shack and tested the SWR on some spot frequencies. Slowly the resonant frequency rose. In the end I chopped off about 3 feet/1metre off the long side of the OCF, making it about 20m in length - a half wave on 40m. Lowest SWR was on the low end of 40m, which was perfect.

Now comes the part I didn't expect! Being a half wave dipole I was expecting a reasonable SWR on 21MHz as that is the 3rd harmonic - the SWR was off the scale! BUT the SWR was low on 7, 14 and 28MHz - EVEN harmonics.

One other frequency has a low SWR and that is 18MHz, I presume that the 10 feet of coax that acts as a top fed vertical radiator is having some effect there. The SWR on 50MHz is about 3:1 so operation is possible on that band with the ATU.

So we have low/lowish SWR on 40, 20, 17, 12, 10 and 6m, and very high SWR on 30 and 15m.

There are only two bands I cannot use the antenna on and they are 160m (obviously!) and 60m (I don't have an NOV so that is not an issue). However my Wellbrook loop works well on those bands so I can receive on them.

For a 20m long antenna that I have fitted into a 7x6m garden I am very pleased with it. There are full details and pics on my website .

Tuning an antenna just before a contest isn't really the best idea because any manner of things could go wrong! Luckily Murphy was away annoying someone else that day and it all went smoothly. I have noticed that resonance changes according to the weather. I guess this is due to the close proximity of wood to the antenna (it is mounted on a 10m dead tree and all the supports are wood).

Once it has been up for a couple of months I will do some further resonance checks and compare them to the original to see if there are any noticeable changes. It is useful to do this from time to time as it enables you to spot possible problems, such as a poor connection, water in the feeder etc. If there is a significant change in readings it is worth investigating as the sooner it is found, the easier it will be to fix (in theory at least!).

Watch this space for more reports on the skywire.

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Setting up the blog

Digimode happeningsPosted by Sean Gilbert Sat, July 31, 2010 19:32:49
I thought it about time I had a 'proper' blog! I have a couple knocking around on the internet somewhere but this is the first time I have set one up properly with a dedicated address and RSS feed subscription (sounds technical - It's not, it's just a way of keeping up to date and having a notification when I post something to my blog). So what has been happening digimode wise? Well ROS is still being developed and is still attracting just as much press (good and bad). It's an interesting mode but it can be rather frustrating to use, especially if you are in a QSO and someone starts sending on the same QRG as that effectively means QSO over!! There are a few niggles with it, such as not being able to key in a tx/rx switch into a macro, so you can remain in transmit mode until youre member to switch it back to receive. I have been busy with JT65 and WSPR, both have produced good results from my 5-10 watts. My signals have been reported on the West Coast USA, something that is rather pleasing to me. PSK has been busy, lots of stations active we just need beter conditions on the higher bands. It seems that the Sporadic E meter has run out of credit this month as there has not been much heard above 21MHz. Very pleased with the way the new OCF antenna is working (details on, particularly on 40 and 17m. 73 de G4UCJ ...-.-

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