I’ve never had a decent aerial for the 30m (10 MHz) band and have struggled to work much on the band either with my old doublet or the inverted L that I’ve had up for the last couple of years.
About a month ago, I realised that I could hang a single band 30m dipole in the space that I was previously using for an off centre fed dipole. I’ve tried an OCFD a couple of times now but they don’t seem to work well for me.
I make no secret that I still consider baluns a magic art and I’ve not taken the time to get my mind around balun construction yet. In theory, I should be able to do this as I’ve wound so many wires around ferrite cores when I’ve been making filters and QRSS/WSPR transmitters that it’s become second nature. I’m just not comfortable with the idea of building baluns.
The largest rally in the UK is the Newark Hamfest which takes place in September every year and I was hoping to pick either a commercial 30m dipole or a suitable balun when I went but sadly I didn’t see any of either of them. Shortly after returning from the rally, I ordered a pre built dipole which as delivered a couple of weeks ago.
Although it’s not been particularly cold here recently, we’ve had a fair amount of wind and rain and this weekend was the first chance I’ve had to do anything.
The first thing I had to do was clear the bushes from the support pole at the end of the garden. I generally lower and raise my wire aerial a few times throughout the year but it’s been two years since the last time I did that and there was about three yards of undergrowth to clear (note to self: a hedge trimmer really isn’t suitable for this kind of job, a chainsaw would be far more useful). This took a good hour to clear and has made it obvious to me that I need to make the effort over the winter and clear the end of the garden properly.
With that clear, I was able to lower the paracord I use to hold the end of my wire aerials and then get the centre support pole down. I don’t like leaving the centre of my wire aerials just dangling so I have a 25ft pole in the garden which is strapped to a washing line end post.
It was straightforward enough to fix the new dipole to the centre support pole and lift it back up again.
Here you can see the centre pole, the dipole and the far support pole. Note that it’s well clear of the overhead power cables which are behind the pole.
I didn’t get a chance to properly test it straight away but I did make a couple of quick QSOs using FT8 and although the internal SWR meter on my TS-590SG showed below 1.7:1, I had to use the built in ATU to persuade it to transmit full power.
This morning I put my Mini VNA Tiny on the dipole and was surprised to see that the SWR was a lot worse than the rig had showed me at around 2.4:1 in the centre of the band (2). It was most resonant at 9.9 MHz (1) but wasn’t particularly good there at nearly 2:1.
To feed the dipole, I used the length of RG-213 I previously had connected to my inverted L and added a run of Westflex 103 up the pole. To save me having to run backwards and forwards to the shack to check after each adjustment, I took my laptop outside, disconnected the Westflex 103 from the RG-213 and made my measurements there.
I had to lower the ends and chop three lengths off before I got the aerial tuned correctly. In total, I took just over six inches off from each side which brought it bang into the middle of the band.
You can see the results of my trimming below – The SWR is flat over the entire band (it’s only 50 kHz wide) at a fraction over 1.6:1.
The two markers are the band limits.
When I connected the aerial back to the wireless, everything was much better than before. The rig transmits full power without needing the ATU and the internal SWR meter reads unity.
I had a quick session this evening and have already worked a couple of new countries on 30m so it’s having the desired effect straight away.
The downside is that I now don’t have any aerial up for 160m, 80m and 60m but my SG-237 smartuner is now free and I’m wondering if I can string a loop around the garden somehow.
Here’s the dipole from the other side – Note again that it’s well clear of the cables you can see running across the picture.