Today’s activation of Cairngaver was mainly to try out my new end-fed antenna and matching unit. Experts disagree on whether or not you need a counterpoise when end-feeding an antenna which is a half wavelength long, or multiples of half a wavelength. However, Steve Yates AA5TB has put a lot of thought and common sense into this. On his excellent website http://www.aa5tb.com Steve describes a matching unit for 40M to 17M.
I more or less copied Steve’s design, and added a Dan Tayloe N7VE resistive SWR bridge, assembling it in a small plastic box. The resulting matching unit weighs just 80 grams, and will match an end-fed half wave antenna on 40M, 30M and 20M.
Today I used a 20M long piece of PVC covered 24/0.2 wire, weighing about 200 grams. I had previously trimmed it to resonance according to AA5TB’s instructions. Being a resonant half-wave on 40M, it will also work on 20M as a full wavelength, requiring a similar high-impedance feed.
Based on an experiment at the same summit last week, I set up the antenna as an inverted vee slung over a tree, with the apex up 6m, and arms at about 120 degrees. As suggested by AA5TB’s theory, I used no counterpoise at all. When set up in this way, everything was completely stable, with no susceptibility to hand capacitance effects. Apparently the FT-817, key and headphones provide a sufficiently high impedance return path for the antenna to kick against.
Results? On 40M with my 2.5W output I got 599 reports from France and England, 589 from Switzerland, and 569 from Norway. Changing to 20M, requiring just a tweak of the tuning knob on the matching unit, I got 599 reports from Bosnia Herzegovina, Czech Republic and Switzerland. Looks like Steve Yates AA5TB is right!
Very interesting. I have often thought about this approach but was not sure about the high voltage feed so steered clear of it.
So is your tuner a true Fuchs design with no earth link between the primary and secondary windings or have you made it like Steve AA5TB (in one of his circuit diagrams) with an earth link between them (which makes it a half wave/LW with a tunable coil at the end)?
It’s interesting to note how much the Fuchs design is mixed up with the other. I have had some email exchanges with DL hams to clarify this point. Apparently even the ARRL got the Fuchs circuit wrong in one of their books!
Anyway it sounds like it worked a treat in the end. I guess you could also use the legs of the wire as the guys for the pole and not have to worry about a counterpoise (which would be nice).
Thanks Marc. It’s not a Fuchs design, it’s the same circuit as AA5TB’s with link and tuned circuit windings both connected to “earth”. Earth in this case is the combined metallic mass of the transceiver and accessories.
I’m completely sold on this approach now, for simplicity and weight considerations too. One you get over 60 you become conscious of every additional gram you have to lug up the hill! The little tuner weighs just 80g, and the antenna 200g. So with my SW40+ at 300g, 8 AAs plus holder at 220g, Palm straight key at 80g, earbuds, notepad and pen at say 100g, I have a complete station weighing under 1Kg.
I have been using a W3EDP antenna which is a 25.6 metre wire fed from the top of a parallel tuned circuit and using a variable counterpoise. The first version of the tuner used a 22 turn coil 50 mm diameter with the feed from the rig tapped in about 7 turns up from the earthy end. This covers all bands 80 m to 20 m. In a later rebuild I fed the coil (now wound on a 35 mm film container) with a secondary winding and found no difference. Furthermore, there was no difference between having the link coil share the earthy end with the primary coil or floating. By experiment I found that 5 metres of counterpoise sufficed for all bands including 5 megs, but the antenna would work without a counterpoise on 20 metres. The antenna is set up as an inverted V and the counterpoise is laid out on the ground.
This sounds like a similar approach to the designs described above. The W3EDP antenna has considerable antiquity, having been designed by cut-and-try methods in the 1930’s. It gained a considerable and well-deserved reputation as a DX antenna, and has a lot to recommend it for SOTA.
Sadly I have only ever used 2m from Cairngaver, when an HF operation from there looks like a lot of fun.
I would like to return to GI to finish the Mournes and to activate more of the County Armagh summits. However, the access and security situation is always worth checking for the latter.
In reply to M1EYP:
You’re right Tom, it’s not one of the Mourne Mountains at all, but the highest of the Craigantlet Hills.
When you come back to GI give me a shout and maybe we can do some joint activations. As part of the Peace Process those mountaintop forts along the border have been demolished, so access should be better.
In reply to G8ADD:
Yes, Brian, I thought of the W3EDP for some time, but 25.6M seems a lot of wire to wrangle. On the other hand it will work on a more frequencies than an EFHW. Hmmm… I think there’s still enough wire on that reel…
As well as removing the hilltop border forts, has the Peace Process sufficiently discouraged the coordinated theft from cars parked in the GI/CA (County Armagh) hills? There are many tales and warnings on t’internet about cars parked on Slieve Gullion GI/CA-001 while people go for a walk on it! Hopefully this situation is in the past though.
I would like to complete the GI/MM (Mourne Mountains) and GI/CA regions in future trips to Northern Ireland - if it is sensible to do so! I would also like to start the GI/SW (South West) and GI/SM (Sperrins) at some point, but that is a more long term project.
The Antrim Hills (GI/AH) are an interesting and diverse set if anyone is heading over that way, but the best GI SOTA walk yet is definitely the pair of Slieve Donard GI/MM-001 and Slieve Commedagh GI/MM-002 walking up the Glen River Path from Newcastle. Highly recommended - as indeed it was to me by the GI Association Manager, Colin GI0RQK.
I have had one slung over the house this past academic year. Local noise levels here are appalling, but it did allow me to work the odd activation on 60m using just my FT-817.
In reply to M1EYP:
Tom, I’m surprised at you. No-one in South Armagh would ever just steal things from cars. The local rogues are much too busy with the regional specialities - cattle rustling and diesel fuel laundering.
I would love to activate Slieve Donard, but little Cairngaver still seems like quite a hike to me. I should get in training and then maybe the next time you’re over we could do a joint activation?
It would be good to see some more SOTA activations in GI as it is a rare association.
My Mum was originally from Northern Ireland and my Grandad Jimmy (retired sea captain) still lives there in Larne in County Antrim.
Me and my Dad M1EYP were in Northern Ireland doing some SOTA activations and we did an evening activation of Carrigatuke GI/CA-003 in County Armagh and both my Mum and my Grandad Jimmy were not happy with us for going into County Armagh due to the crimes that happen there.
In reply to M3EYP:
Thanks Jimmy - it’s not called Injun Territory for nothing(no disrespect to the Native Americans). If we all went in my old banger maybe someone would do me the favour of nicking it.
73
Ken
In reply to GI4FLG:
The EFHW has been a great addition to my SOTA kit. It has freed me from carrying a bulky bundle of feedline and given me better performance than any of the dipoles and verticals I had been using in the field.
I was also inspired by the AA5TB documentation. After about a dozen “rewinds” of the impedance transformer/inductor described therein, I found that a single winding, tapped inductor gave considerably less transformer loss and fewer parasitic problems.
I’ll attempt to post pictures. I’ll happily e mail them to anyone interested.
Stu
Thanks for the info, Stu. I take it you mean an autotransformer circuit, which I haven’t tried yet.
You may be interested in the single component no-tune EFHW matcher Nick Kennedy WA5BDU describes on his website Nick Kennedy's Page
Apparently if the impedance of the secondary of the transformer is high enough it will work without a resonating capacitor. I think this must be the secret of the fabled PAR End-Fedz matchbox, a very compact no-tune matchbox which will work with any half wave HF wire antenna, ideal for SOTA ops. I intend to make one of these next.