[ICOM] G5RV & AT-500

[Alan Leith]

Hi Joel,

The main thing I have against auto tuners is that they are built to 
protect the transistor output stage of the modern 
transceiver.  That's why I am perturbed by the 17M SWR with the G5RV.

In fact, nothing much has changed from the original installation, 
except that one leg goes over a tree branch whereas before, it was 
drooped considerably and the end insulator just met the branch.  This 
time I pulled it a little more taught.

My SWR is quite reasonable (so the meter says) on 80 CW, 40, 30, 20, 
15, 12 and 10.  On 80M I turn off the AT-500 and use the internal 
tuner in the IC-761 when I want to go onto SSB between 
3.750-3.800.  I think what I am going to do is to put together a 
dipole for 17M and get it up about 40-45' and that will take care of that.

Of course I don't know the actual impedance on any band, but the mere 
fact that I am getting out is good enough for me.  It certainly isn't 
my triband beam but I never had any expectation that it would compare.

Thanks for your comments.

73

Al, VE1AL
____________

    At 10:10 AM 7/28/2006, you wrote:

>Al,
>
>I'm not sure exactly what the AT-500 is, but would guess that it's 
>an auto tuner. They are great, but one limitation is that on most, 
>you can't tell what the settings are. The fact that it tunes to 
>1.35:1 doesn't say much about the antenna impedance, since it will 
>likely tune a wet string as well, and from the shack you can't tell 
>which you've got.
>
>The best diagnostic step I can think of, other than taking it down 
>and measuring all connection resistances - as has been pointed out, 
>it doesn't work well with one side disconnected, is to measure the 
>SWR, or even better the impedance at the bottom on each band. I do 
>that whenever I put up an antenna and then can tell if it has changed.
>
>My G5RV, many times broken and reconnected, hence shorter -  has the 
>following measured SWR (average across band) at the bottom of 100 ft RG-213:
>
>80/75; 5:1
>40; 2.7:1
>30; 10:1
>20; 2:1
>17; 2:1
>15; 7:1
>12; 6:1
>10; 3:1
>
>Yours may well be quite different, depending on actual lengths, but 
>it should be somewhat like this.
>
>GL & 73, Joel
>Joel Hallas, W1ZR
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>Alan Leith wrote:
>
>>I've finally raised by G5RV again, after it came down a few weeks 
>>ago in an accident.  An old tree fell across one end and...well 
>>that's not the problem.  Anyway, before it fell down, the antenna 
>>was performing well on 12, 17, 20, 30, 40 and 80.  I tune the 
>>antenna with my AT-500 and SWR was below 1.5-1 on all those bands.
>>
>>When it went back up today, I was able to tune it on the same bands 
>>EXCEPT 17M.  For some reason, while I can tune it down to 1.35-1 in 
>>the pre-set mode, once I switch to auto tune, the SWR goes up to 
>>3-1 and the power output is cut to 50W.
>>
>>As far as I know, nothing has changed, except that this time, I 
>>pulled one end tighter (I had not done that the first time) and 
>>about 3 1/2 feet of the end is folded down over a tree branch.  Is 
>>it possible that this has made an electrical difference in the 
>>length of one leg?
>>But why does it tune so well on all bands except 17, on which it 
>>worked perfectly well before?  I'm not interested in using the 
>>antenna on 10 or 15.
>>
>>Can I do anything to fix it?  It is the only antenna I can put up 
>>for 17M and that's one of my favorite bands.
>>
>>Help.
>>
>>73
>>
>>Al, VE1AL
>>
>
>
>----
>Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>Icom Users Net: Sundays, 1700Z, 14.316 MHz
>Icom FAQ: http://www.qsl.net/icom/
>
>
>
>--
>No virus found in this incoming message.
>Checked by AVG Anti-Virus.
>Version: 7.1.394 / Virus Database: 268.10.4/402 - Release Date: 7/27/2006


-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.1.394 / Virus Database: 268.10.4/402 - Release Date: 7/27/2006