Sunday 14th February is the Harwell radio rally. Some of our members have been and greatly enjoyed it in the past. It’s in Didcot which is not too far out of our patch. I’m sure if there is sufficient interest we can turn it into a club outing… Anyone interested? Login and vote by leaving a reply to this post.
Further details can be found about the rally at: http://www.ntay.com/hars/rally_pre.html
Andrew
G0RVM
Just spotted these short videos and thought they may be useful….
Ham college: http://www.hamcollege.tv
Andrew
Santa was kind enough to get me a new SDR radio this year 🙂 It’s very different and will take some getting used too.
Andrew
G0RVM
OK, so this is not a technical video, but I just love the simple overview of HF communications not to mention some of the historic artefacts present at the old base.
Enjoy 🙂
I really enjoyed this video, perhaps as it goes places I’ve been but perhaps also because of its lightweight approach…. Makes you think we could do the odd trip as a club?
Andrew
G0RVM / VP8CES
A great video. Thank you RSGB.
Amateur Radio: A Hobby for the 21st Century
Over the last few years I have not had to think too hard about ensuring I’m driving my FT-2000 at a good level. i.e. its not being overdriven. It has an Automatic Limit Control (ALC) meter and its been a matter of adjusting the audio amplifier gain such that the ALC triggers occasionally and only on the highest signal peaks. If a good quality transmitted representation of the input signal is to be produced its essential that the equipment stages are not overdriven. I guess we all rely on the ALC and its correct adjustment is second nature, however, take away the ALC function and what do you do? How do you ensure you don’t overdrive the radio or downstream amplifiers? This is the problem I had 🙂
I’m using the FT-2000 as an exciter for my Kuhne Electronic VHF transverter. In this mode the ALC circuitry of the FT-2000 no longer works and the transverter does not output a drive level signal which I could connect to the FT-2000 or to a homebrew ALC meter. But the transverter does have a red ALC LED which illuminates when the drive level becomes excessive.
The signals I’m presenting to the radio are audio and are either voice from the microphone (voice chain) or data from a SignaLink USB audio interface (data chain). Each of these chains has several amplifiers which can be adjusted by an operator:
Ensuring each amplifier is set to a level such that downstream equipment is not overdriven producing distortion and splatter is essential!
So, how did I adjust everything? Well, the transverter documentation says to start by setting the radio to full power (0.1mW when using the transverter connector) in RTTY or CW modes and key the transmitter, then adjust the TX Power control of the transverter to output 20 Watts which should be prior to ALC LED illumination. Having done that using a constant CW modulated signal I had the transverter generating maximum power for a maximum signal drive level from the radio. That set the upper threshold which could not be breached by the voice or data chains without distortion or the transverters ALC activating.
Next I fed the constant CW, RF output of the radio directly into my digital oscilloscope rather than the transverter and noted the signal power. Interestingly, the power levels seemed much higher than the figures stated in the FT-2000 Operating Manual. But from the previous step I knew the transverter was ok with this.
CW Transmission
This allowed the accurate identification of the RF power level driving the transverter and thus the baseline levels for the voice and data chains. The next step was to generate a constant RTTY tone using the computer and adjust the amplifiers in the data chain such that the levels identified in the first step where not breached.
RTTY tone generated by DM-780
Once done, I performed a similar exercise on the voice chain for J3E (SSB). By selecting a cumulative display mode it was possible to record the varying power level over several iterations of a CQ call. As can be seen, most elements of the call resulted in an average level, but interestingly, the ‘G’ or Golf in G0RVM generated significantly more power.
J3E SSB Voice adjustment
The gain of the voice amplifiers in the voice chain were adjusted so that the upper threshold identified in the first step were not breached. The last step was to adjust amplifier gain for A3E (AM). I had expected this to be very similar to the J3E level but it needed to be slightly higher.
A3E (AM) Transmission
AM is not a mode I use very often, if at all, so I didn’t spend too much time adjusting amplifier gain but I did change the gain from the factory default to ensure that the upper threshold identified by the first step was not breached. It could still go a little higher but it will do…
So, the result of all this testing is that I am now confident that using the voice or data chain’s I’m not going to overdrive the radio or transverter. Downstream of the transverter is an RF power amplifier, but that is specified to generate 1kW for 25 Watts of drive, and as I don’t wish to run it at full power, overdriving should not be an issue.
I’ll just add at this point that the above approach is applicable to amplitude modulated signals only and thus not those that are frequency modulated.
Andrew
G0RVM
I could not resist the name of this article, it seemed so obvious 🙂
I’ve been in the radio room this afternoon listening to the 2m VHF band, calling CQ on CW and listening to the beacons. The Scottish beacon, GB3ANG in IO86mn near Dundee has been perfectly readable for extended periods which is pretty amazing for a station using a 4 element Yagi and 20 watts.
http://www.youtube.com/watch?v=j8TYKrmpfrY
Andrew
G0RVM
Back in the 80’s I received my first amateur radio license, a ‘B’ license as it was back then entitling me to use, if I recall correctly, bands above 30 MHz only. We didn’t have 6m and 4m band allocations then so it meant 2m and 70cms were the bands of choice for me and the majority of other ‘B’ license holders.
So I started with 2m and 70cms SSB and my interest was soon peeked by space communications with Oscar 10 etc. Those early Oscar’s were excellent as, if I recall correctly, they where in elliptical orbits which meant that they appeared to hang in the sky for some time, not shooting overhead as do satellites in lower more circular orbits. Their transponders were just like big SSB repeaters in the sky and I worked all over Europe. Happy days. But working those Oscars was not that easy especially at Acquisition of Satellite (AOS) as they were pretty far from the Earth so a good station was needed. My station grew to a 2m, 9 element crossed Yagi; a 70cms, 19 element crossed Yagi, both circularly polarised; azimuth plus elevation rotators and mast head preamplifiers. The radio was a Yaesu FT-736 which I only sold last year…It was a wonderful radio.
Of course with those antenna’s it was perfectly possible to work terrestrial communications too. I made contacts across the UK and Europe using sporadic E and Tropospheric propagation. Those were exciting times indeed as not only was amateur radio new, to me, but it was such fun learning about different types of propagation, satellite communications and having great fun talking to people.
Ok, so by now some of you will be asking – what is the point of this article? Well, bear with me… I learnt Morse code and in the early 90’s received my ‘A’ license. Soon afterwards the world changed as I started doing radio professionally for a few years. This removed all interest to do amateur radio stuff when I got home from work. Anyhow, time passed and I started to operate on HF talking to people all over the world – it was fascinating – I learn’t lots more.
With solar cycle 24 rapidly fading and with the real possibility that cycle 25 may be no better, probably worse, I’ve been looking back and found myself comparing my V/UHF experiences with those of HF.
My conclusion is that HF is fun, its pretty easy to work stations across the UK, Europe and further afield depending on your station. Take a minute and think about that, especially the ‘depending on your station’ bit. Do you have the space to erect, for example, a 9 element Yagi for the 20m band? I’m seriously impressed if you do 😉 I bet most of us are using simple HF antenna’s and we are constrained by space, interference and the cost of erecting a high-performance HF station. But move on up to VHF and things get so much easier. I bet many of us could erect a 9 element Yagi for the 2m band and mount it several wavelengths above ground too…. Such an antenna will cost a tiny fraction of its HF equivalent; its small, light and easily rotated too. Interference does certainly exist above HF but its nowhere near as bad. But, FM repeaters and modes such as D-Star aside, VHF is dead these days I hear you say? I cannot deny that it is much quieter than in the 80’s and 90’s but its still a happening place… Its perfectly possible to work stations using phone and data modes across the UK and into Europe when propagation is flat. All those exotic data modes are present and in active use too, people are exploiting Tropospheric propagation, meteor scatter, satellite communications, auroral propagation to name a few.
So its back to the future for me, the HF antenna is now down and until I receive my new VHF antenna I’ve elevated one of my original 9 element Yagi’s. Already I’m hearing beacons GB3ANG in Scotland, GB3VHF in Kent and GB3SSS in Cornwall. I even worked an old friend towards London using CW (RST:559) and Olivia with 20 watts. Who says VHF is line-of-sight. 🙂
I guess you realise the message by now…. V/UHF is lots of fun, you can work DX, high-performance stations are much more achievable than on HF and you learn lots. Amateur radio is so much more than HF, FM, repeaters, D-Star etc. So, why not explore our higher bands?
Andrew
G0RVM
The Kempton rally takes place 8th November.
Andrew