46 and counting…

Ok, not quite antenna meltdown but possibly not too far from that. You know, or at least have reason to suspect, that there’s something wrong with your antenna system if the SWR starts to vary during transmissions. I have noticed this in the past few weeks but thought little of it, other than to touch the ATU (SEM TranZmatch z-match) between transmissions to see if it was getting warm, which it wasn’t.

A few words by way of explaining my normal way of operating. Mindful of having a relatively weak signal I tend not to call CQ a lot unless I’m working PSK31. I find it more productive to work stations that I can hear, strong or weak, because I at least have some chance of a QSO if there is at least one way propagation.
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Dean Amateur Radio antenna, ATU, propagation, SEM TranZmatch, SWR, z-match

If you have read any of my previous amateur radio related posts you may by now be well aware that I don’t have the best of antennas.

To be perfectly honest it’s a bit difficult to gauge just how much of that is mere perception due to relatively poor conditions these past 12 months but, compared to more efficient resonant wire antennas or exotic beams, my end fed wire is at best what they call a ‘compromise’ design.

This antenna is known variously as the ‘no counterpoise antenna’ or an ‘end fed Zepp’ - it is physically a long wire radiating element fed with a balanced feed line. It is usually constructed from either a 50ft or 25ft length of twin feed line (bell wire or speaker wire can also be used) where one of the wires is cut at the mid point and removed. The longer wire forms the radiating element and the remaining twin lead is the balanced feed line. My current installation employs a raditor of some 40ft with a 20ft feed line (having been sized to fit into the limited space available).

In this configuration it is an unbalanced antenna fed with a balanced feedline which results in the feedline also radiating. The most interesting property of this design however is the radiation pattern: For all frequencies that the antenna will load up on, the distributed current maximum stays at or near the center of the antenna where the twin lead stops and the single conductor (radiator) continues. This gives the antenna a radiation pattern very similar to that of a resonant half wave dipole, except that unlike a half wave dipole antenna being used as multi band antenna, the radiation pattern and current distribution remains intact over the full range of frequencies tunable for the antenna! This means nice low angle radiation with decent gain over a broad range of frequencies (using a tuner) without having to adjust the antenna length. Well so says the theory at least!

As you can see - on the face of it, according to the theory, this should be a good multiband, compromise antenna. It has the additional benefit of being end fed which for my setup is the only option when it comes to feeding an antenna. However, I will be reserving judgement for now because I am still not entirely convinced that it is working as well as the theory suggests it should.

Dean Amateur Radio antenna, SEM TranZmatch, z-match

…are blowing through amateur radio station G0RIF! I have made the decision to finally commit to getting a radio that I believe will be with me for a very long time, a Yaesu FT-950 (pictured). The reason? Digital IF filtering! For too long I have put up with adjacent channel interference, even with the 500Hz filter in the TS-480. With the FT-950 (with the PEP updates) this will be [mostly*] a thing of the past.

In addition I am now moving to a ’single radio setup’ with a single interface unit (MyDel SB-2000) for PSK31 and other soundcard data modes, FSK RTTY, CW keying and rig control.

Yaesu FT-950 HF/6m transceiver

To that end I have agreed a sale on my TS-480SAT that has been a faithful servant for the past few years, mainly used for RTTY and CW. Other gear for sale includes my LDG AT-200Pro auto antenna tuner, my SignaLink USB radio interface, my Rigblaster Plug & Play radio interface and my Yaesu FT-857 radio, used primarily for portable operating.

The net result of this change will be that I have one radio (the FT-950) with one interface unit (the SB-2000) and one antenna tuner (the SEM Tranzmatch - see earlier posts for details). The FT-897D currently in use as the primary PSK31 set (and standby HF rig) will then be used for portable work (as and when required) and will retain it’s role as a spare HF set.

* I do accept that even modern digital IF filtering has its limitations and that there will still be occasional circumstances where signals are so close together (or when one is particularly strong) when interference may still occur. I believe that such occurences will be significantly fewer with the FT-950 than with the TS-480.

Dean Amateur Radio, Life..., Pictures FT-857, FT-950, G0RIF, PSK31, Rigblaster, RTTY, SB-2000, SEM TranZmatch, SignaLink, Yaesu

I don’t think my previous post about the new antenna said enough about the SEM TranZmatch, which I think is making a positive contribution to the ‘new’ antenna system. In fact I’m prepared to take back any suggestions I may have made in previous posts that this wasn’t in fact a great tuner.

Having previously used an LDG Pro-200 auto tuner I have to say that the SEM z-match is now the tuner of choice at home and for now the LDG is retired to the shelf awaiting redeployment. The z-match is working very well and if nothing else now allows silent band changes at night - a welcome change from the noisy LDG which can only be likened to shaking a can full of ball bearings while it tries to find a match!

Dean Amateur Radio antenna, SEM TranZmatch, z-match

My results in the recent WPX contest certainly suggest that is indeed the case. A new antenna for just £2.99 - how could that be?

To be perfectly honest it’s not an entirely new antenna. It’s probably about 90% of the wire previously used in a sloper configuration to which I have added an 8ft clothes line prop/pole. The clothes line prop is lashed to the back fence at the point where the old antenna was attached to the fence, only now the end of the antenna is some 7ft highter than before with corresponding increases along it’s length, all the way up to the shack window at about 25ft.

The antenna wire, end fed at the top, is now shorter by about 10ft and there are some issues on 40m where I need to limit power to no more than 40 watts. However, on 30m and above it is working fine. The SEM TranZmatch (z-match tuner) gives good matches on all bands 30m-10m and results on 30m and 20m are particularly encouraging (which was a great relief having undertaken this work the afternoon before the WPX CW contest started where 20m would be the band on which my efforts were concentrated). A few contacts were possible on 15m but conditions weren’t great so I’m reserving judgement on the 17/15/12 and 10m bands until they start to open up as cycle 24 develops and propagation improves.

So, for a sum total of £2.99 and a little effort, it seems I have a new, improved antenna that, for now at least, has renewed my enthusiasm for the hobby that was previously a little bit flat based on recent experiences with the previous form of the antenna. It’s still a seriously compromised setup but given the limited possibilities at my location, as long as it works, it’ll do for now!

Dean Amateur Radio antenna, propagation, SEM TranZmatch, Solar Cycle 24, z-match

I think it was John Lennon who said that time you enjoyed wasting wasn’t wasted time. I subscribe to that view entirely but this past weekend was just time wasted and certainly wasn’t very enjoyable.

First of all the weather was terrible…then it was lovely…then it was terrible again…and so on and so on, all weekend. Alternating sunny spells and showers (of varying intensity), all to an almost meticulous hourly cycle. Very difficult to make any plans when trying to get out and operate some portable amateur radio.

Then the technology (or my understanding thereof) let me down. A new doublet antenna I had high hopes for didn’t seem to work very well at all (see ‘An inconclusive test’ below). Time will tell if the new z-match tuner (SEM TranZmatch) will prove to have been a worthwhile purchase.

Then on Sunday, when despite the weather I did get out portable with my 17m vertical dipole (one of the Par End-Fedz), I heard what would have been two all time new ones in the form of Madagascar and St Helena but both stations were buried beneath serious pile-ups with no hope of a QSO in the time I had available. Oh well - another time maybe.

Maybe on reflection I’ll consider it mostly wasted weekend. I did at least get a few contacts in the log and I did learn a little bit about doublet antennas and balanced feedlines. I’m sure I’ll have better luck as the weather improves through the summer and I’m able to spend more time out and about with the portable station and maybe, just maybe, that doublet will come good after all.

Dean Amateur Radio, Life... doublet, portable, propagation, SEM TranZmatch, vertical, weather, z-match

Not quite what I was expecting or hoping for. I’d read a lot about how well a 44ft doublet antenna worked when fed with a balanced line. Unfortunately my little test this afternoon left me a bit disappointed because I certainly didn’t see the kind of performance I expected. I’d taken the time to construct what I thought was a pretty well made antenna. I’d got the right kind of feed line and I’d found myself a good balanced tuner in the form of the SEM TranZmatch (pictured). I was hoping for great things. For one reason or another though the antenna was very difficult to tune on all but 17m.

SEM TranZmatch

I tried all the bands that the antenna is designed for with the exception of 40m. This includes all of 10m, 12m, 15m, 17m and 20m. I wasn’t able to try 40m due to time contraints and some pretty grotty weather (see yesterdays post).

Using a Yaesu FT-857, my transceiver of choice for portable work, I connected the radio to the TranZmatch with a separate SWR meter in line, connected the antenna to the TranZmatch with 20m of 300 ohm ladder line and set about 17m which wasn’t in great shape but did seem to have the usual early afternoon clutch of Asian stations (including VR2XMT, Charlie, coming in loud & clear as usual).

I tuned the TranZmatch for maximum noise on receive and then tweaked it with a bit of RF - quick & simple and a low SWR <1.2:1 across the band. I tried to reply to a few CQ calls but either wasn’t heard or just wasn’t getting out. I didn’t hang around trying to work stations though because this was primarily a test of the antenna/feedline/tuner combination so I moved on to see what 20m was like.

It was at this time that I got the first inkling that all wasn’t quite as I’d hoped. Getting a good match on 20m was really difficult and the lowest SWR possible was no better than 2:1. Now I know this isn’t terrible but I was hoping that the TranZmatch would do better. Maybe I was expecting too much because the same was then true on 15m, 12m and 10m. All of these bands had very sharp tuning and a minimum SWR no lower than 2:1.

I have a few questions in my own mind as to where the problem might lie. Is the feeder a ‘bad’ length - at twenty metres long it’s a full wave on 20m and might just present an extreme mismatch to the tuner. This doesn’t explain why other bands should be just as difficult to tune. The doublet wasn’t level - it was in an inverted-V configuration and the included angle was probably a bit small at around 100 degrees - 120 degrees is recommended. There was a lot of ’spare’ feedline just lying on the ground, loosely coiled - is it better to trim the feedline to prevent this?

For now the jury is out and I have more work to do before deciding one way or the other whether or not I’ll adopt the 44ft doublet as one of my regular portable antennas. And it’s just started raining again!

Dean Amateur Radio, Pictures antenna, doublet, FT-857, ladder line, portable, SEM TranZmatch, SWR, weather, z-match

I have recently been considering a number of antenna options for portable operating - something I seem to spend a lot of time doing since getting the ‘portable’ bug earlier this year.

From an article titled ‘My Top Five Backyard Multi-Band Wire HF Antennas’ by L. B. Cebik (W4RNL) I have selected the ‘broadside doublet’ as my next little project. Being a balanced antenna and requiring a balanced feed line I have also been exploring suitable antenna matching units and have decided that an old Z-match design should work well.

With that in mind I found an ad for an old SEM Transmatch unit and called the seller to do a deal. To my surprise he told me he’d send me the unit immediately and suggested I ‘pop a cheque in the post when it arrives’. Not at all what I was expecting from a commercial dealer and to be honest, a refreshing change from kind of sellers often found on eBay where nothing happens until your money is firmly in their hands (so to speak).

I am now looking forward to receiving the tuner and experimenting with a 44ft long doublet fed with 300 ohm ladder line. All I need now is a bit of decent weather…or is that too much to ask?

Dean Amateur Radio, Life..., Totally random antenna, Cebik, doublet, eBay, ladder line, portable, SEM TranZmatch, W4RNL, z-match