Category Archives: News

Propagation forecast tools

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Many thanks to Peter (and his able assistants) for the informative presentation on ‘Propagation Forecasts’ this past Wednesday, I found it fascinating and very useful.

On a related note I happened to stumble across the following news on the RSGB website:

The RSGB Propagation Studies Committee has begun work on a new web HF propagation prediction service. It will feature both area coverage predictions as well as point-to-point on-demand predictions. Presently, only area coverage has been completed and this can be seen at www.predtest.uk. This will soon be followed by the P2P predictions. It is planned that following these trials the RSGB website will host the predictions. Comments and suggestions are invited by Gwyn Williams, G4FKH via email to g4fkh@sky.com.

The site itself (screenshot at the top of this post) also mentions that the Python source code behind the new tool is open source and available on GitHub.

Please share your own propagation tools with us in the comments below 🙂

Harwell Radio & Electronics Rally

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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 

My New Shack Home QTH

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Progress is taking a pace in the completion of my new purpose built radio shack/home office. Some say I’ve been banished finally to life in the garden whereas I would argue the serenity of peach and purposeful entertainment ….oh and some work thrown in I guess!

Plans are for HF, VHF and UHF antennas to be located and installed behind the shack. I have a purpose built store room on the far side of the shack which will house remote tuners if required, rotator gear and other ham radio ‘bits’ as my better half calls it all.

I really hoping that when it come to installing equipment in particular my antenna systems and perhaps the rest of the gear I might call upon a few members who might want to help me with that. I’m also more than happy to ‘loan’ out my shack for other members to use and perhaps experiment with particularly when it comes to VHF/UHF developments.

I intend to purchase a hex beam for HF and then work on my home brew projects.  Currently have 4 home brew antennas waiting for modification before I decide which one’s to install when the shack is ready….VHF(UHF) Parabeam (late 80’s) will need rotator … a must, a J pole (slim Jim design)..that’s going up somewhere, and some old CB stuff …an original 5/8th wave vertical Hygain Super Penatrator (left over from my CB days), an original Avanti Astro Plane (basically a co-inductive J pole that has a capacitance hat and is omnidirectional), a modified dipole that intend to use on 6m. I am about to take delivery of another beat up old Avanti PDL2 beam (a basic bi-polarised double fed antenna). These were legendary (as were Moonraker beams) back in the day. I intend to modify it for Ham use not sure which bands yet but considering VHF/UHF after reading Andrews post. A fellow Ham has modified his for 6m.

Busy but fun times ahead. Looking forward to it.

Mark M6KMJ

Drive levels…

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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:

  • Voice chain:  3 x microphone and 2 x RF amplifiers
  • Data chain: 2 x audio and 2 x RF amplifiers.

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

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

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

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

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

TSGARC – A short history

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In September 1987 I joined the Thornbury Radio Club as I had recently passed the Radio Amateurs Examination (RAE), in those days we met in the upstairs hall of the United Reformed Church (URC).

We had a variety of radios at our disposal and a large hall, so if conditions allowed we were able to have smaller meetings around the hall; CW in one corner, a radio operating in another and maybe a group stood nattering about all things Amateur Radio, oh and computers were just making themselves known so we were also looking at packet radio and amateur television broadcast and receive.

But now for a short history.  The Thornbury Radio Club was formed in early 1980 by Alan Jones G8AZT after running the first RAE in Thornbury.  This, however, was not the first club in Thornbury.  During the late 60’s and early 70’s there was a club that met, as it happens, at our current location, the Chantry.  This club obtained the callsign G4ABC but when the club ceased it passed to a couple of members in Chipping Sodbury where it remained unused.  But during the 1980’s it was offered to the newly formed Thornbury Radio Club.  During the club’s expansion in the 80’s members also joined from area’s a little further afield: Wotton, Dursley, Yate and Chipping Sodbury.  To reflect this larger catchment area the club changed its name to the Thornbury and District Radio Club.  But in the early 2000’s the government disbanded Avon county and replaced it with South Gloucestershire, so the club again changed its name to reflect this new division, becoming the Thornbury and South Gloucestershire Radio Club.

We were a club of about 40 members in the late 80’s and into the mid 90’s. Then we started to lose members, either because they were moving away or because the stage after retirement caught them up. So for the period from then until about August 2008 we struggled on with a nucleus of about 12 to 15 members, then we had to vacate the hall for refurbishment, so for nearly 9 months we were offered the HQ of GX0WOI the local Scout radio station at Woodhouse park. Finally in May 2009, we were able to move back into the newly finished URC Hall! But it was not a good period as the hall had been finished with aluminium clad insulation boards in the roof, a highly gloss laminate floor and shiny gloss walls, the echo and cold feeling made it impossible to do anything resembling radio activities, so we were forced to find alternative accommodation.

Finally in August 2009 we were able to rent on a long term but weekly paid rental the Tudor Room in the Community Association premises, this just worked with 10 members but was not ideal. Over a period of time we negotiated the installation of both VHF and HF antenna’s, so things improved and we were gaining new members. The search began again for a larger room, after talks with the Chantry staff, it was agreed that we could trial the Buckingham Room in November and December of 2012, finally, in January 2013 we negotiated a similar deal for this room as we had for the Tudor room although it was about £4 per week dearer. A team exercise one weekend saw us transfer the antenna feed points to the Buckingham room.

Today the Buckingham room is the home of the Thornbury and South Gloucestershire Amateur Radio Club (TSGARC) where it meets each Wednesday evening.  Click here for further information.  Being one large room it has space to accommodate the club which continues to grow and now has 35 members.

Many thanks to Alan G8AZT for information about the earlier clubs.

Stan G0RYM