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Re: Possible SWR problems with 70cm antenna, more info



My thanks to Sebastian and all the other kind folks who have reponded to my 
query. A little more information seems to be in order. My rigs here are an 
Icom 820H and a 706 MKIIG. I can test with either. The antenna used to work 
when I had a TS-2000X and An ARR preamp. I had to get out of the radio game 
awhile and sold both those. In addition to the rigs mentioned above my mast 
mount preamp is  now an Icom AG-35.
 I did do some swapping around of cables between when it worked and now but 
I've checked all of that I know to check. The cable between the shack and 
preamp reads good with continuity in the center conductor and the shield and 
no shorts in between.
 If you are familiar with the driven element design on Kent Britains's 
"cheap yagi" antennas you will understand that the coax  between it and the 
receive preamp will read a dead DC short. However, I have disconnected the 
coax from the element and I have continuity in the center conductor and 
continuity in the shield with no shorts between them..
The behavior of my 820's meter is such that if I key the rig on 70cm on high 
power, the needle of the meter pins to the max. It's always been my 
experience that this can sometimes be an indication of some type of problem 
in the antenna circuit. I don't really wish to leave either rig keyed until 
the SWR protection kicks in.
It's not hard to get to the antenna so I guess I'll go over everything 
again. Unfortunately there is not a 70cm. repeater within range of my QTH 
for me to test with. At least not one with published frequencies that I can 
find.
BTW I don't even own a dummy load, HF or otherwise, I know I need one but my 
budget is very tight right now and I'm lucky to have the gear I've got. I'm 
also kind of a lone wolf, I don't belong to any clubs where I can borrow 
equipment. Years ago when I used to work at HRO and needed a meter, I'd just 
borrow the store display model overnight! I miss those days...hi hi
Tnx and 73,
Michael, W4HIJ
----- Original Message ----- 
From: "Sebastian" <w4as@bellsouth.net>
To: "AMSAT-BB BBs" <amsat-bb@amsat.org>
Sent: Tuesday, June 03, 2008 10:20 PM
Subject: [amsat-bb] Re: Possible SWR problems with 70cm antenna


> Michael, I doubt a 2 meter SWR meter will give you any type of useful
> information for 440.  Many are rated for 1.8 Mhz - 148 Mhz or similar.
>
> Before you blame the antenna, take a look at your coax, primarily the
> connectors.  Make sure the connectors and the coax don't twist if you
> attempt to move them.
>
> You didn't mention what type of rig you are using.  Or how difficult
> it would be for you to get a close look at the antenna.  Since it's
> homebrew, whatever system you used to match it, might have moved.
> Consider testing it on the FM part of the band, and see if your rig
> complains.
>
> If it doesn't, then that's your answer.  Your tuning method isn't
> working.  Or, try using a local 440 repeater and see if a local ham
> will loan you an SWR meter that will work on 440.
>
> 73 de W4AS
> Sebastian
>
> On Jun 3, 2008, at 8:33 PM, Michael Tondee wrote:
>
>> I'm having some problems with a homebrew lineasrly polarized "cheap
>> yagi" for 70cm. I don't have any success hearing myself on VO-52 or
>> AO-7. This antenna used to work reasonably well for both.  The way
>> the power out meter on my radio acts, it leads me to believe I may
>> have an SWR issue. Unfortunately I don't own or have access to an
>> SWR meter or anylyzer capable of working at 70Cm.
>> I'm going to take a wild shot in the dark here and ask the bb
>> because I sure don't know. Would it be possible to put my 2 meter
>> SWR meter in the 70cm line and at least get a ballpark figure of
>> SWR? Or would the reading be so far off, it would be useless?
>> I'm not intending to try and tune the antenna in this manner, I just
>> want to get some indication as to if SWR is indeed the problem.
>> I must confess I don't know what the frequency range determining
>> elements of an SWR bridge are. I must have missed that at some point
>> or the other.
>> Any other ways to determine if I have an SWR problem without a
>> meter? It's just not in the budget to buy one right now.
>> Any suggestions are appreciated.
>> Tnx and 73,
>> Michael, W4HIJ

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