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swr rings on a99
Topic Started: 15 May 2010 - 17:54 (3,053 Views)
Fixerman
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108 Charlie Tango 300

hi, i managed to buy an A99 secondhand and was wondering if anyone could give me a starting point for where the rings need to be placed for 27.555 as a start for setting the swr. I'm mounting it on a 12 foot pole on gable end of the house. I should add that it has the firestick top section on. I'd like to get it in the ballpark before i get it up in the air, i've built an ugly balun for it as well.

cheers

fm
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Unless been played with leave them where they are, test with an swr first of course. Mostly all come fine and dandy tuned for the triple
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VoG
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If I remember my A99 correctly, the rings were about an inch and a quarter, inch and a half, down from the top of the threads.
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Fixerman
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108 Charlie Tango 300

As it came the swr rings were wound tight to the top, just wondering if thats the way they should be, second hand so i don't know the history of it and what its been used for previously.

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Offplanet
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26 Charlie Tango 104

Mine ended up around the position that Steve quoted - I did find that my original installation required the rings to be much nearer the top, however after I installed the Ugly Balun, the rings needed to be set in the lower position.

I suspect that due to the fact that my A99 was originally fitted to a very short aluminium pole, the coax braid was becoming part of the antenna - when the Ugly Balun was fitted, the issue was eliminated and the tuning of the antenna was restored closer to it's defaults.

Maybe the previous owner had a similar set-up, but if you've the Ugly Balun in place, a good starting point would be about 3/4 of the way up.

When I installed the Firestik type top section, the SWR actually dropped slightly and no adjustment was required. I used the top of the UK block (almost 28Mhz) and just under the alternate SSB calling freq (26.285Mhz) as the top and bottom set points for tuning the SWR. SWR around 27.555Mhz is excellent.

Quite often though, there's no substitute for climbing up the ladder a few dozen times!

Cheers
Gary
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Firetrap
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Mine are about 2cm from the top of the threads for great SWR on 27.555
Edited by Firetrap, 16 May 2010 - 12:24.

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VoG
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Firetrap
16 May 2010 - 12:23
about 2cm from the top
Therein lies the perfect example of the age difference on this site.

I, in my advanced years, refer to, "an inch and a quarter", and that young whipper-snapper Firetrap says, "about 2cm". LOL
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PigSticker
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26 Charlie Tango 269

I bought mine from new and the SWR was crap and had to adjust the rings all the way to the bottom and even then it wasnt right so I fitted an RF choke and now it is 1.1 to 1 right through EU and UK bands, not sure on the 555 as I dot have a sidebander yet.
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HomerBB
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2 Charlie Tango 004

I've learned the RF choke beneath the A99 is a necessity in some applications. I use one on everything I put up with a coax.
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VoG
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HomerBB
5 Jun 2010 - 15:45
I've learned the RF choke beneath the A99 is a necessity in some applications.
Can't argue with that! I've used an air-choke / RF-choke / Ugly-Balun on all my 11m Verticals since I found what a difference they CAN make

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PigSticker
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26 Charlie Tango 269

thats a bit of a fancy one compared to mine!
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Cherokee
5 Jun 2010 - 21:42
HomerBB
5 Jun 2010 - 15:45
I've learned the RF choke beneath the A99 is a necessity in some applications.
Can't argue with that! I've used an air-choke / RF-choke / Ugly-Balun on all my 11m Verticals since I found what a difference they CAN make
hi steve' where can i buy one from please !!! fed up of qrm
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VoG
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porky.69
7 Jun 2010 - 10:38
hi steve' where can i buy one from please !!! fed up of qrm
Hi Paul - An Air-choke isn't a universal panacea for QRM but, in my opinion, it certainly can help and it is a classic "Can't do any harm" type of addition. I've never seen an Air-choke for sale, although you can buy a 1:1 Balun which does the same thing.

Beware though, I bought a one-to-one balun on Ebay and about three months later the solder to the inside of the SO259 failed and I had a million-to-one SWR. It couldn't be repaired as the black box containing the torroid had been filled with bathroom sealant. I wrote to the guy I bought it from to tell him, but didn't even get a reply.

The thing in my picture (Call it a RF-Choke, an Air-Choke, or an Ugly-Balun) was knocked together in my workshop one evening

It comprises 12" of (brown) plastic pipe left over from the shed guttering project which has been wound with about 18'-odd of co-ax, and then a PL259 fitted on each end. Obviously you wouldn't want the air-choke pressed flat against a metal scaff pole holding the aerial, so I added a couple of legs made from some left-over plastic electrical conduit and two "C" shaped feet made from splitting a bit of bathroom drainpipe, all hot-glued together. Then, finally, a couple of cable ties to fix it in place and a female-female/SO259-SO259 connector so it can fit inline with the aerial cable.





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thanks steve
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Offplanet
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26 Charlie Tango 104

The main purpose of an Ugly Balun (RF Choke) is to help cure RFI/EMI/TVI as it helps prevent the coax braid becoming part of the antenna (which leads to RF in the braid - RF in the braid is a big cause of RFI/EMI/TVI).

It not really for reducing QRM on receive, although some operators have commented on a reduction, and a reduction in SWR is also commonly reported.

I'm in the same school of thought as Steve and Homer and install some form of RF choke on any antenna fed with Coax.

I've seen recommendations on installing one at the radio end of the coax as well.

Cheers
Gary

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The CTX Experience - imagination and drive
Callsigns - 26-CTX-104, 26-CT-104, 163-CTX-104, 163-CT-104

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thanks gary i suffer from a wee bit of static now and again ...would love one like steves' photo to try but cant' find any anywhere
on the web
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Offplanet
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26 Charlie Tango 104

Pretty easy to make one Paul - also look at earthing options for keeping the static down.

Cheers
Gary
The CT eXtreme DX Team [imgw=50]http://i643.photobucket.com/albums/uu157/offplanet_photos/mountain.png[/imgw]

The CTX Experience - imagination and drive
Callsigns - 26-CTX-104, 26-CT-104, 163-CTX-104, 163-CT-104

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CB, PMR446, SOTA, IOTA, SHTF Comms, Homebrew and some other stuff on - www.youtube.com/ukcbtv
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I will make you one Paul. I'm doing the same so while I'm making one I can easily do two!
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maybach52
8 Jun 2010 - 17:23
I will make you one Paul. I'm doing the same so while I'm making one I can easily do two!
thanks gary. and thanks very much bob im very grateful ...it will be a great help :clap:
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Wizzbit
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163 Charlie Tango 008

Apologies in advance if this is considered "an old post" but I was wondering about the ugly balun.

I'm awaiting a nice 10 meter length of coax then I'm going to make one.

What I was wondering is how come there is such a mixed opinion on the optimum winds/length ?

My first idea was to use a pop bottle but I would prefer to use some plastic pipe like suggested. Can you actually buy such a short length?

My plan is to make one that is in one piece (ie no double pl259s to connect it to the main feed.

Any help would be great.

Cheers

M
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