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Atas 25

I seem to be struggling with my recently purchased ATAS 25 and was wondering if anyone on here can give me a bit of set-up advice. (apart from throw it in the bin!)

Remember it is designed to be mounted on a vehicle made of steel (ie. a rather large conducting ground plane). Unless you set it up on a similar ground plane, you can’t really expect it to behave similarly. It is a very small whip with a relatively high inductance loading coil and would be likely to have higher losses than a longer antenna with a low loss loading coil made of very thick copper wire.

Give more details of what you are doing, how you have resonated it, what its apparent impedance is and I’m sure a few dozen opinions will surface.

73
Andrew VK1DA/VK2UH

[Edit: I mistook the antenna type for the mobile whip series. The above comments are not entirely appropriate]

Not having a crystal ball and without any context from you of what you were trying to do you, your question boils down to “how long is a piece of string?”.

So a bit of info of what you tried and what did and what didn’t work and I’m sure you’ll get plenty of suggestions to help you get it going.

I am looking for a bit of general setting-up advice as the instructional leaflet is perhaps as best described as a waste of a tree.
I suffered patch-lead problems yesterday and also think the aerial is more sensitive to tuning that I was giving it credit for, but on a cold Gunn conditions were not the best to be playing around with something new.
Mounted on a mini tripod as recommended by Yaesu my first contact was Sweden on 14 Mhz but then barely made the trip to The Cloud on 2M.

So what is the problem? Can you not get a match? SWR high? Tuning has no effect?

You did try the frequently given advice on here to set it up and test it at home before trying it in the wilds?

There is some detail here: http://www.eham.net/reviews/detail/3980
on the experiences of others including a SOTA activator.

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Different ATAS I think, The 25 is the field portable manually tuning one

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Oh yes, a different one. Sorry, my mistake. I’ll retire before I’m hurt.

Andrew VK1DA/VK2UH

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Of course I didn’t! LOL

Hmm, my cup of sympathy seems dry!

OK, as you found, setup of a loaded shortened vertical is critical of lengths. This a base loaded whip and it will be very sniffy about the ground you mount it above and any big bags of salty lard (the operator) close the antenna.

My own off-centre loaded vertical is sensitive to the environment and I spent some time in the garden setting up and learning how to set the adjustments, taking it down and repeating the setup to my calibration marks before I took it out. Hundreds of activations later I can look at the ground and know whether I’ll need to go long or short of the calibration marks. If you don’t have an antenna analyser or accurate SWR meter then you will have fun learning to set it up. Consider borrowing something like an MFJ-259 as the FT 817 SWR meter, for example, is less than perfect.

Then you follow the Yaesu instructions in setting it up. They say alter the length. Well if you set it for 14MHz you can measure with the analyser where it has ended up (higher or lower in resonant frequency) and adjust accordingly. The issue will be that if this behaves the way mine does, the settings are quite critical, changes of a couple of mm are enough to move it 50kHz when near resonance. That’s why a 259 or similar is great as you can faff about with the lengths and see all the time what is happening. When you find how to set it for any band, mark the lengths with a felt pen. Dismantle the antenna, set it up again to the marked lengths and see if it is repeatable. It should be. You need to do this for all the bands you want to use. I’d expect damp string to be as good as this will be on 40m, but it should be OK on 20/15/10. As the book says no guarantee it will tune on 17/12 but you may find a way to do that. The higher you mount it the better it will work. Keeping the radials elevated will help too (a bit of dowel, old tent pole is ideal).

Learning to tune it will require some patience and practice. But once you have practiced doing it, the setup becomes straightforward and automatic. It will help in the field if your radio transmits out of band… you can setup for 21MHz and then squirt a bit of RF in and measure the SWR and if it’s way off, squirt a bit of 22MHz or 20MHz in for a second or two to see if you need to go longer or shorter.

It wont be a DX magnet but it should be usable on 14MHz and up with a fair degree of success.

For 14MHz and up, can you beat a simple groundplane antenna though?

4 quarter wave lengths of wire + some RG58 for the feeder.

Total cost best described in pence, and zero technical skill required to build one - trust me, I’ve built 6 and they all work.

Oh, and they ARE all a “DX magnet”.

Only downside I can see is they are all single band antennas, so lack multiband capability. Having said that I have got one with SOTAbeams traps inserted that works on 10m and 6m.

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Hi John,
.
There’s one and only one arbiter of how good any antenna is and that’s a SOTA Activators log book. There ain’t no arguing with a log book.

73 Mike

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Couldn’t agree more with Mickey on this one!

37 S2S QSOs in the recent 3 hour NA-EU event, including 9 EU-NA S2S. 66 QSOs in total, all with 5w from an 817 via my homemade simple groundplane antenna.

I’d say that was a pretty good antenna?

Thank you…and very helpful.
I was trying to rely on the swr meter on the 817 yesterday as numpty here forgo one of the patch leads. Not a good start!

In my experience the 817 SWR meter is a best for go/no-go indication.

3 blobs or less is fine
4 blobs is go and tweak something
5 blobs or more is something is broken, fix whatever is broken!

Quite right Mike.

Incidentally, how did the Eu-NA event go for you? I always felt you should have the epithet “DX magnet”!

I checked it against the SWR meter in my ATU. AFAICS it isn’t measuring SWR at all, it is measuring the amount that the gain of the PA is reduced to protect it, so any indication at all indicates reduced output - the 817 indicates one bar at an indicated SWR on the ATU of 1.9:1. This may just be a peculiarity of my 817, but I would suggest that any blobs at all is a bad idea.

Brian

I would suggest something in need of a tweak Brian. The meter is not brilliant and worse on VHF/UHF than HF and ISTR power level has an effect too. Both of mine indicates no reading for less than 1.5:1 on 60-10m at full power setting on 12V. What it reads on the other bands I wouldn’t know. I’m happy with my advice that 3 or less is FB, 4 means fiddle with it and 5 or more means fix the breakage.

My experience (and I mean exactly that - experience of using the 817 on approaching 2K SOTA activations, rather than any technical nous) - tells me that I agree with Andy’s interpretation of the 817’s “SWR meter” indications.

Maybe. I might try it again sometime with a different patch lead, some of mine are ancient. However, it is worth looking at the KA7OEI FT817 pages - as an example, on 14 MHz for a Z ohms=200 he finds 4 bars = 4:1, Z=68, 1 bar = 1.4:1 and Z=8.2, 4 bars = 6:1. There is a lot of useful information there, and it is clear that there is a lot more to the SWR indication than counting bars!

Brian