Random jottings

[M1BUU]

Well, that turned out to be my best winter bonus period ever, quite unexpectedly. The weather has been so dry, with a distinct lack of snow. My crampons and ice axe haven’t left the shed this year. It was nice to make double Mountain Goat whilst out with G4TGJ on Fountains Fell on a beautiful sunny day.

I had a bit of a last minute push earning 72 points in the last week of winter bonus, it certainly pushed my average step count up a bit!

I’ve been having a bit of a tough time with my gear since the end of last year, my rigs have been OK but the power leads and my antennas are all failing due to age. I made the power lead for my MTR back in 2012 and I’ve had to resolder it quite a few times recently. I think the actual copper strands have had enough. Now that the winter bonus period has finished, I think that I need to have a period of sorting out my gear. I need to manufacture some completely fresh power cables and antennas.

MTR power cable, broken again!

SOTAbeams Bandhopper 3, failed when I wanted an S2S - I twisted the broken wires together and made the S2S!

SOTAbeams Bandhopper 4 needs fixing

I’m running out of antennas to use now, so I really need to get some made. I’ve been experimenting with end fed half wave antennas but I’m finding it really hard to get the antennas to work on multiple bands. I made a 40m efhw with a link for 30m. The 30m section works great, but I can’t get a tune on 40m that also works on 20m. I’m thinking that maybe I just need to go with links for each band. In most cases I’m struggling to get the VSWR below 1.4:1 at best, altjough I find the VSWR improves as I raise the feed point.

I think I still prefer dipoles over the end fed antennas.

I note that the QMX SSB firmware beta version has been released. The QMX has huge potential to take on the Elecraft KX2. Imagine a trail friendly QMX+ with built in auto-ATU. Amazing to think that Hans has created such a complex and high performance radio! I have the hi-band QMX, but I think I should have got the mid-band version in hindsight. I got the QMX with SSB in mind. Ultimately I’d like to run a QMX on 40m SSB with an EFHW for bicycle based trips. I’m wondering if I could make a low Z tuner for that final tweak to bring an EFHW closer to 50 ohms for the rig. I think a little tuner in an Altoids tin would be great. I have the ALT tuner based on a design by KD1JV, but I mean just a standard unbalanced antenna tuner in a SOTA friendly package.

Lots of work to do in the M1BUU shack, including installing my new 100Ah lithium leisure battery which I’ve had for a few weeks. I need to reprogram my solar controller with new parameters, which I’ve been putting off!

73, Colin

[MW0KXN]

Hi Colin,
The 49:1 EFHW works well and is worth persevering with to resolve the issues. There are dozens of SOTA activators reporting good results using Steve’s @MW0SAW QRP EFHW built onto a Sotabeams winder.

@M1BUU

I can’t get a tune on 40m that also works on 20m.

I suggest trying a 2m counterpoise if you aren’t doing so already, or alternatively a 2m length of coax to act as a counterpoise.

73, Kevin

[M1BUU]

Hi Kevin, I’m using just over 2m of coax to feed the EFHW. I did the wavelength x 0.05 calculation. I wound a choke into one coax feeder but I have an intermittent connection in that cable, I’m not sure that my cheap RG-174 likes being wrapped around a small toroid core. I was as careful as possible and the turns are fairly relaxed. It could just be the BNC that’s intermittent I guess.

I haven’t found a difference using either the plain coax or the coax with choke.

I built a MW0SAW style antenna but I ended up cutting the wire too short trying to get it to work on multiple bands. I might just cut the wire down a bit to a different band - I could add in a link for 30m and use fresh wire after. I’ve been experimenting with different values of capacitor, I’ve seen mostly either 150pF or 100pF used.

I have been using an EFHW on 30m recently and I have made QSOs and qualified. I was using the EFHW yesterday on G/NP-006 and made 19 QSOs.

EFHW on Stony Cove Pike G/LD-018

73, Colin

[G4OIG]

Hi Colin,

Like yourself, I’m a dipole man and have been since the start of my HF activities in SOTA. I have constructed a 40m EFHW, 49:1 fed, inv L configuration with counterpoise, but I have only used it with my KX3 with internal ATU, though I would say with great success. I hope you get yours to work to your satisfaction.

I really don’t know which is best, dipole or EFHW. Activating requires so much effort on my part in terms of planning, travel, cost and time that I tend to err on the side of caution and go with what I know works for me. I expect to continue using dipoles with the FT-817 (with and without an amp) and the EFHW with the KX3.

I do have an LDG Z11 auto-ATU and that was used to good effect with the EFHW enabling me to make a contact on 80m from a HEMA summit when there was no propagation on other bands and I assume the same would have been the case had I owned the KX3 at the time.

73, Gerald

[G4VFL]

We did a study at my company when I worked and found, unsurprisingly the lack reliability of circuits was depended on the number of connectors the circuit passed through not the MTBF of the electronics and cable. The more bits that can be poked, pulled and got back to front is the problem. So when I dream up any SOTA gear I bear this in mind, and still get it wrong but not too often.

73 de

Andrew G4VFL

[MW0KXN]

Hi Colin,
Having read your previous posts I should have known that you would have undertaken a rigourous assessment of the EFHW and addressed the obvious causes of problems before making this post.

Cheers,
Kevin

[F4LEK]

I’ve been experimenting with my EFHW lately, trying to solve the impedance matching issue. The challenge arises because the raw impedance on lower bands, like 40m, can be significantly higher than on higher bands, such as 20m, even with the same antenna configuration. For example, in my garden, I measured about 6000 ohms on 7 MHz compared to 2700 ohms on 14 MHz.

• Since the impedance varies across different bands, having different transformers (e.g., 49:1 and 81:1) can help achieve a better match.
• Use of links
• Using small, movable inductors on the wire to shift the resonant frequency on higher bands, as described here
  
  

I tried to make a multitap transformer. Like this

It works, at least in my garden, though I still need to test it on different types of soil. So far, it does a good job of matching different impedances. Additionally, I noticed that adjusting the number of turns on the secondary winding slightly shifts the resonant frequencies. It seems to act somewhat like a tuner, possibly by adding some capacitance or a similar effect. Read more.

[M1EYP]

Yes, Steve @MW0SAW‘s Excalibur antenna is fantastic. It misses the WARC bands though. I have actually “forced through” some 30m S2S QSOs (with you Colin @M1BUU) on this antenna, but it’s probably not “best practice”!

I know 30m is your favourite band. Why not build a monoband quarterwave vertical with groundplane? It’s a lot of wire and requires a 10m pole of course, but it is better than a dipole or end-fed for working DX. I’m planning some dawn greyline DXing sessions with mine shortly.

[M1BUU]

Hi Tom, actually, 30m isn’t necessarily my favourite band. I like 20m/17m/15m. I’m forced to use 30m to chase @G4TGJ, it’s all his fault! Once I’ve got the 30m capable antenna up, I can rarely be bothered to swap it.

I don’t have a 10m pole. I do have some tired 20m and 17m home brew groundplane antennas, one of which I need to refurbish for May.

73, Colin

[G4TGJ]

@M1BUU

I’m forced to use 30m to chase @G4TGJ, it’s all his fault!

I usually do 20m too, even if I have only alerted for 30m. You just need a little patience…

[MM0FMF]

@G4VFL

depended on the number of connectors

This.
I learnt this from making really big computers that went in submarines. Connectors were the cause of most failures and if you had to have connectors, their use was carefully monitored. This went as far as the back plane connections for CPU cards (there were many boards). Boards could only be plugged/unplugged 25 times if they were going into a production system before they were scrapped. Too many insertions leads to failures and if you absolutely have to launch your nuclear weapons then you can’t have intermittent connections in the systems.

[M1EYP]

@M1BUU

30m isn’t necessarily my favourite band

My bad. I just got that impression from the amount of times I’ve seen you spotted on 30m recently. But admittedly, no proper data analysis has taken place…

@M1BUU

I don’t have a 10m pole

I normally use a standard 6.7m fibreglass fishing pole or a mini 4m one (with the Excalibur). But I did buy a SOTAbeams Travelmast for a holiday in EA8 some years ago, and this is just about long enough for a quarterwave vertical & elevated GP on 30m.

@M1BUU

I need to refurbish

I’ve done less refurbishing since switching to the military spec. green wire from SOTAbeams, and to chocolate boxes for connecting it all together rather than twisting wires/soldering/taping over.

“I’ve had this groundplane antenna for 15 years. In its time it has had 4 new driven elements, 9 new radials and 3 new feeders.”

[MM0FMF]

@M1BUU

struggling to get the VSWR below 1.4:1

Why?

[M1BUU]

Because that’s as good as it gets! I’ve tried with calibrated NanoVNA and my QRPometer. I think it’s to do with feedpoint height and ground/counterpoise. The higher the feedpoint, the better the VSWR. Resonance seems to be pretty constant.

[MM0FMF]

Do the radios care? Are they happy at 2:1? If so then sure aim to get the mismatch low but don’t obsess about it.

Or if it bothers you, clone Codan PA stages. All of my Codans are rated for short to open and everything in between with full power indefinitely 100%

[M1BUU]

I’m not obsessed with perfect VSWR.
My FT-817 doesn’t care. My MTRs seem fairly robust but the QMX panics if the VSWR is a slight bit high and disables the transmit. It is possible to alter the QMX behaviour in the menu though.

I ran a QCX on 17m for an hour during the QCX WARC QSO party, only afterwards did I realise that the antenna I’d made some time ago was linked for 15/17 and 20m. I’d been thinking it was a 17m antenna and I’d had the 20m links in the whole time! Didn’t measure the VSWR but the QCX seems fine.

[MM0FMF]

QCXs don’t seem to be affected. The QDX PA is the sensitive one to high power into a poor match. The QMX PA is very similar but the QMX has lots of software monitoring things and stopping badness before it’s bad. Advantages of using a very fast CPU instead of an old donkey like the AT Mega

I cloned my 40/30/20 trapped EFHW using a pair of taps from SOTAbeams and the lengths from my other antenna. I haven’t adjusted anything yet. Using a 49:1 it measured like this when strung as an inverted-7 (drooping Inv-L)

40m 3.3:1 ???
30m 1.7:1
20m 1.7:1
17m 3.3:1
15m 2.7 :1
12m 2.6:1
10m 3.7:1

The 30/20m readings are fine, just the 40m needs looking at. I tested it when I had dropped my coat down the hill and wasn’t thinking straight as I was in a rush to activate and find the missing coat. That means I never tried it with the 64:1. Nor did I see whether it was long or short. When it is used with the KX2 and tuner it’s always perfect. But I do need to fix it on 40 so I can use it with the QCX.

[G8CPZ]

@G4OIG

I really don’t know which is best, dipole or EFHW

Best for what? Best for whom? There is no ‘best’ antenna only ones that score high on multiple factors that you care about. I use EFHWs or linked dipoles or my Cha MPAS Lite vertical depending on summit topology, weather, intended bands, propagation conditions, time available and sometimes just coz I fancy taking a particular one.

[M1BUU]

The answer is dipole is nearly always best!

My particular use case for EFHW was for when I went to the inner Hebrides supported by bicycle. The EFHW was a lighter, more compact choice. The EFHW does seem to be a little bit weaker on TX and RX - note the word seem - I don’t have measurements.

But… it’s fun to experiment and like you say, there are certain situations where a particular attribute is desirable. I just need to find someone who will trade a mint KX2 for a bunch of working home brew rigs!

[M5RJC]

@MM0FMF

Boards could only be plugged/unplugged 25 times if they were going into a production system before they were scrapped. Too many insertions leads to failures and if you absolutely have to launch your nuclear weapons then you can’t have intermittent connections in the systems.

Indeed, oft encountered in military systems.

I remember one I worked on in the 1980s where the OTP PROMs had to be soldered into the processor boards. No sockets allowed, so the PROMs were programmed then soak tested 7 days on a staging system before being allowed into the wild.

Rick