Hallo Matthew
Take a look at DK7ZB… I think in the chapter about 2m/70-Yagis ultralight you will find good hints
https://www.qsl.net/dk7zb/start1.htm
73 Armin
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Thanks for the link, I’ve not seen that site before.
The part I can’t quite work out is shown in the image below (adapted from a worldwidedx review). The conductor (red line - my addition to the image) must be soldered to the BNC, and presumably passes through some insulation (grey lines - also my addition) within the connector block. I can solder the conductor to the BNC after first passing it through the connector block…but when I then come to screw the BNC into the connector block, the 90-degree bend in the conductor will prevent the BNC screwing into the block.
Perhaps I would need to have a second solder joint at the 90-degree bend - rather like right-angled connectors. But somehow that doesn’t seem like the right way to do it.
A BNC that push-sits into the connector block, with some way to ensure good electrical contact would be easier but no such thing seems to exist.
(image adapted from worldwidedx review])
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BNC is 3/8 UNC thread IIRC. You’ll need to have the block tapped and drilled. You’ll really need another antenna to measure as you need to get the correct thickness of wire and the hole diameters right as it forms the capacitor in the match. Of course you can try to copy it but without a genuine item to copy it all becomes a lot harder in getting the dimensions right and then you’ll have fun and games seeing if you can get an acceptable match.
That’s why I suggested copying an example with dimensions etc. as they are likely to be the easiest route to success. Of course, a wise man puts the given dimensions into the formula to ensure what is on the web is accurate as many who made ribbon J-pole antennas will attest. Or make DK7ZB feeds which just work.
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I was hoping i could reverse engineer the arrow antennas gamma match close enough that there would be sufficient adjustment of the tap along the driven element to achieve a match.
I can always try other methods later if i fail.
Of course, the main reason for doing it is that I saw the price of the arrow antenna (£150) and thought i could make a clone much cheaper.
Of course, i will end up spending £300 on parts, several weeks of time and end up with something that doesn’t work. But should learn a few things.
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[quote=“M0MZB, post:44, topic:25767, full:true”]
Of course, the main reason for doing it is that I saw the price of the arrow antenna (£150) and thought i could make a clone much cheaper.[/quote]
Which model are you looking at that is GBP150? My 2m 3-element model was about $80, which is closer to GBP60 (too lazy to do the currency conversion). Of course shipping is a factory, but I can’t see shipping being GBP90.
Chris
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This! I work at the sharp end of custom silicon designs for leading companies. There are so many things that all of you own that will include some of our silicon designs but NDA’s mean I can’t say. We’re helping our customers get their multi-billion transistor designs working. It’s cool seeing a new model of car come on sale knowing you helped in getting the customer’s software to work.
But that is nothing to the pleasure I get from making antennas from a few bits of wire cut and arranged just right and being able to have QSOs with them. So do persevere with this Matthew, even if it seems to take forever and you seem to never make any real progress. When you actually succeed you wont be able to fit the grin on your face.
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Standard business practice with US products sold in the UK is to convert the $ to £ but leave the numbers unchanged. So an $80 product becomes £80 then you add taxes and duties. And then you add profit margin and something to cover the fact the dealer is responsible for warranty claims. The price can climb alarmingly fast.
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Think i have worked it out.
Apparantly extended length chassis mount bnc are a thing…the solder cup for the centre terminal extends around 20mm from the flange of the socket
So after screwing the bnc into position the solder cup will be accessed through the top exit hole of the block, just like on a right angled pl259 plug.
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Do you have a source? I think that sort of thing could be a nice solution to have in my back pocket when presented with a similar problem.
Chris
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Gotcha. I haven’t seen that with the things I buy or price for work (I’m a 'merican, but work for a British company). Maybe it’s a factor with dealing with small companies like Arrow?
Chris
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Here’s an example…only around 5mm or so extra thread length, but enough to avoid having to extend the terminal by soldering a wire that would then be flapping in the breeze.
Extended thread bnc chassis mount
Doesn’t say if it is 50 ohm though
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If you skim the websites of shops selling amateur radio kit in the UK and compare the prices with those offered by similar shops in the US you’ll see the pattern, but just as an example, a basic KX2 is $950 in the US and £995 in the UK.
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An alternative to copying the Arrow.
Unless you are absolutely wedded to a gamma matched yagi design, there are other designs that are easier to home build, and some result in the elements being stored and carried in the boom. 50 ohm direct feeds are readily available by choosing the appropriate spacing of elements. Maximum gain resulting in ~20 ohm feed impedances can mean the gain is only a few fractions of a db greater than a 50 ohm feed that does not need a gamma match. And reliability, lower parts count and field repairabilty are pretty important at the high end of a 10-15 km climb.
The Arrow antennas are excellent designs and work well. They were originally intended for satellite users, not SOTA. But for home brew, it is hard to beat simpler designs that result in the same performance, or so close to it that nobody can tell the difference.
Here is a 4 element yagi that will cost you very little and will work very well.
73 Andrew VK1DA/VK2UH
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I have taken the ideas from the link below and used Alum tig road and banana jacks / plug for the yagi mount on a 1/2" pvc pipe boom. Light and some of the elements fit inside the boom for storage.
https://www.qsl.net/dk7zb/start1.htm
I have also made a moxon with stellar results.
https://www.qsl.net/dk7zb/Moxon/2-m-Moxon.htm
Malen
VE6VID
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There are many ways of symmetrising… in my personal opinion gamma adjustment is not the best. It is mechanically from the boom to one side and I think it changes the radiation a bit to the side with it…
73 Armin
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Really kind of everyone to respond.
I will try the electrical conduit antenna as a vhf SOTA antenna.
I am primarily building the arrow as a back-garden satellite antenna for 70cm/2m and as an exercise in making something nice…so will probably persist with the arrow design too.
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You have to factor-in the eye watering prices now charged for postage between USA & UK (both directions). Two price hikes last year now make it cheaper to ship anywhere else in the World - US citizens who can should have their delivery sent to either Canada or Mexico and drive across the border 
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Another one !
73, Éric
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Don’t forget that UK prices include 20% VAT whereas US prices are always plus tax (and I think only charged if you live in the same state as the retailer). That doesn’t account for the full difference but I think in the UK we may have greater consumer rights which has a cost. The US is a large single market which will help lower prices. Perhaps the UK could consider being part of one…
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Even if you take that 20% off the UK price is still nearly 20% up on the US one. That’s the dealer overheads, shipping, etc. at work… 
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