30m SOTA antenna options

Equipment Antennas
21

My 60/40/30 dipole has lasted almost 19 years, but I agree, it’s less than ideal when it comes to deployment. That’s why I constructed the 40/30/20 dipoles (I have two versions) which are somewhat easier. Also the popularity of 60m for SOTA in the UK has unfortunately declined over the past decade which sort of supported my decision.

Indeed, that’s why I bought a tunable base coil and constructed my own vertical with flexible heavy gauge wire, utlising a pole for the support to make it suitable for windy summits such as usually found in Scotland. I didn’t fancy a rigid whip disappearing downwind.

22

Yes - indeed. The next iteration of the vertical game will probably be that …

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23

I’m guessing SSB on 30m is allowed in Region 3. I’m glad it’s not allowed in Region 1 as with the larger bandwidth requirement of SSB would make the small 10MHz allocation rather crowded at times.

I’ve noticed that too, which is a pity as daytime NVIS makes it so good for regional and inter-G contacts.

24

This will make things interesting VK < - > ZL with 30 m SSB available on both sides of the ditch.

The 30m band is only available to VK amateurs with Advanced qualification but there are quite a few SOTA operators that use 30m SSB with good inter-VK contacts so it will be good to get some ZL in the log on 30m SSB as well.

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25

Put a link 5m from the feed end of a 20m wire. Swap your EFHW connection from the end to this point. So now you can have a 20m long EFHW or a 15m long EFHW. (Your transformer is on a 3-5m coax). The antenna remains plain wire, you have no tuner, and you can change the bands without walking to the far end

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26

‘Up there for thinking’ …

Would need my transformer hanging off the dipole/guy-rope rather than tied-in between the guy and antenna wire, but no reason that should be a problem …

27

Or with 3 injection points, I could do 30m (full-wave), 60m (half-wave), 40m (half-wave) all within 8m of the wire-end.

28

Where it doesn’t really work is when you are inside a hut and need the 3m of coax to get through the door.

There are clever-arse arrangements of folding or looping-back the end 5m to make it shorter or to bring both feedpoints to the same place. (Clever-arse seldom survives first contact with divaricating scrub.)

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29

Hence the costly (kg, dB) 10m of RG174 coax that I carry.

30

…thanks Matt for your insights re 30m. A great read.

Geoff vk3sq

31

A variation I have not gotten around to trying, is using a slinky spring of ~5m circumferential length stretched out to 1-2m long, at the feed end, with a shorting crocodile clip lead to change the EFHW length from 15m to 20m.

The idea (hope) being that when the turns are stretched well apart, the mutual inductance is low, and it (might) act as the length of wire not an inductor, thus leaving the EFHW multi-band operation and impedances largely unchanged.

This would also allow easy fine tuning of the resonant length from the feed end.

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32

My suggestion is a full-size-vertical:

No antenna tuner needed and you can ofcourse use it on 30 to 10 meter band.

73!
Peter DL3NAA

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33

I also use MFJ 1830 in short or difficult activations. But in a resonant configuration (shortening some cms the whip, as measured with a Nano VNA) with 2 radials of 7.5 m. So I have no need of a tuner. Results are good.

But in normal conditions I prefer a LW of 16.2 m with an ATU.

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34

I’ve used the QRP Guys 20/30/40 vertical on 30m with some success (the coils are switched in and out). There is some variation in the tuning from site to site but it’s usually good enough.

I haven’t tried it yet on 30m, but the Aliexpress red slug whip antenna with the extra loading coil should work on 30m. It works on 40m fine with the coil, and on 20-6 without no problem.

This is even better for constrained locations as it doesn’t need any guys, but isn’t much use on rocky ground as you can’t get the ground spike in.

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35

The whip looks very similar to my Chameleon MPAS Lite vertical which, when used with its supplied impedance matching transformer and counterpoise wires, definitely needs an ATU on 30m to 10m. I don’t believe in trying to change the length of the whip when changing bands. I’ld rather press the ATU button on the KX2, let it go ‘brrr’ for a few seconds than mess around with an antenna analyser.

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36

The QRP guys is a PC board with toroids and switches and works fine.

The Chameleon Hybrid 6:1 balun allows one to tune a 8 ft whip with a tuner as it’s non-resonant on most ham bands

I can erect either and let the tuner do the work if wanted to have more contacts time

John ve3ips

The full quarter wave antenna will be better of course but not always easy to deploy due to a longer radiating length.

I have activated SOTA with a mfj-1020 4 ft 2 0m whip and others with an ax-1.

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37

Progress update:

Well - I’ve tried a few things.

KiSS - simple and rugged, a near-end linked EFHW

I ran 60m over this week’s activations using ZL1THH’s approach of a near-end linked EF60mHW with movable feed point for 40m. Rugged and resilient and promising. An additional link would give me 30m full-wave.

A shorter solution: adding 60m and 30m to an EF40mHW

A look at the Portable 7-Band EFHW Antenna gave some confusing hints that this approach might (or might not) cover both 60m and 30m. Figure 32 shows the 2nd VSWR dip where my simulations put it at 9.5MHz, but Figure 41 shows it bang-on 10MHz - much more useful.

However, construction of the EF40mHW with 25uH loading coil at 15.785m showed the simulations to be bang-on with the 2nd VSWR dip at 9.5MHz. Varying coil inductance vs position could bring that 2nd VSWR dip lower in frequency, but I never got it near enough to 10MHz to be useful. In the end, wind stopped play.

I’d be very keen on details from anyone who’s managed to get this approach to tune on 60m and 30m, as-per figure 41.

Not an ideal approach due to a loading-coil in the second half of the antenna (difficult to deploy / switch in-out / retrieve in scrubby country). But I’d be keen to play with it.

==

Seeking a 60m/30m/??m coil-shortened EFHW.

I’ve lost much hair tussling with 4NEC2 and EZNEC - the dreaded ‘Error 6’ (seems to be something to do with poor handling of VB floating-point arithmetic when running under Wine) leading to me going as far as setting up a MS-Windows VM in an attempt to get it to run error-free. Desperate times indeed.

Then, I discovered that if I hit F12 when running Rob / DM1CM’s excellent online EFHW designer I can override his default selection of inductance, length values and get that to simulate all coil values, coil positions and antenna lengths. Speedy progress ensued.

The designer suggested a 25.675m wire with a 10uH coil 2.5m from the feed point would give me 60m, 30m and 20m.

A build of that indicates it to be viable. I don’t have means of measuring inductance, and had to remove about 30% of the turns off my coil to get things to line up - so I’ll have to test the actual inductance used at a later date. Not clear if my calculation of inductance required was out, or I got the turns required to achieve that wrong.

On the VNA I get VSWR minima at 5.3MHZ, 10.1MHz and 14.3MHz. All three with nil or near-nil complex impedance component. Handling the cable or connectors has no impact on those minima indicating that they are genuine and should be reliable.

Connected to the TX-500 all three show VSWR or 1 or 1.1 when set up in an inverted V at 1m-5m-1m on the SOTApole on flat ground at home.

Looking forward to trying it out in the field to see if it really works in a range of conditions / deployments!

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38

I have built Stephan’s antenna. It was a bit fiddly, but in the end it was resonant on all 7 bands. No particular insight, just trial and error. The downside for bushy environments is of course the coil in the outer portion on the wire.

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39

Couple of questions:

  1. Which 7 bands? Design document mentions: 160m, 80m, 60m, 40m, 20m, 17m, 15m, 10m. But nowhere does it mention 30m.

There are a couple of comments in the reflector thread mentioning 30m. But no indication of what they changed to move the SWR low from 9.5MHz (as shown in the design document) to 10MHz.

  1. If you did get it working on 30m, can you confirm that you mean working without the need for an ATU?

  2. Did you stick to the design inductance and location for the coil? Or did you tweak those values to achieve this result? if so, can you remember how?

Thanks

Matt

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40

First, I made 1:49 transformer for efhw. Then I tune wire for resonantion on 30m. Than I added link and wire for 40m. That also gave me 20m. I put coil on the link to get on 5,3MHz. SWR on 60m is about 2,5 because efhw is usualy low

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