[TowerTalk] Inverted vee

[Roger (K8RI) on TT]

It depends on the ham's reason for wanting a low SWR.
Perhaps they do not want to use an external tuner.

A truly balanced antenna would be extremely rare.  I've never seen one 
on 75 including center fed, half wave dipoles. Open wire hooked to an 
unbalanced antenna radiates as well as hearing noise.  A tuner in the 
rig, only lets the rig see the proper load over a limited range.  
Without a line tuner and an isolation choke at the antenna my modern rig 
would be very limited as to frequency range on 75.

How close does the tuner come to letting the rig see R52, J0? Most low 
power antenna tuners are quite limited as to range on 160 and 75.
OTOH the feed line, open wire or coax can pick up noise and radiate 
signal.  It can be surprising how much noise can sometimes be eliminated 
with a good choke in the feedline at the antenna that was thought to be 
balanced.

For rigs with tune and load controls it's usually  not a problem, but 
many of today's modern rigs don't like to see much reactance .

Mine?  I use an AT5K HP tuner switched between the rig and an AIM. I 
tune the feed line / antenna to R=50, J=0 using the AIM with less than 1 
W, I tune the amp into a dummy load and then switch the antenna to the 
rig.  I depend on R and J being correct and a choke at the antenna 
making the feed line, more or less balanced. IOW a legal limit signal 
with less than a 1W tune up.  On 75, with the legal limit, the voltages 
can get quite high with much of an excursion in frequency.

73

Roger  (K8RI)


On 11/6/2015 11:06 AM, Donald Chester wrote:
>> Hello,
>> I have an inverted vee up about 100 feet. It resonates at 3615. From past experience, how much should I add to each leg to get it down to 3515?
>> Thanks,
>> Carol
> Hams are WAY too obsessed with SWR.  If it's a full size half wave, the difference between an antenna resonant at 3615 and 3515 wouldn't make a bit of difference in performance.
> VSWR at 2:1 or less is perfectly OK.  Even 3:1 will have negligible effect on the signal if it doesn't trigger a fold-back feature in the radio.
>
> I use open wire tuned feeders on mine, and get equally excellent results all the way from 3500-4000, but I use a remotely tuned matching network at the base of the tower. If I wanted to use coax, I would purchase some hard-line (ever cable TV stuff works fine), cut the antenna to be resonant at 3750, and just use it and not worry about it.
>
>
> Don k4kyv
>   		 	   		
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-- 

73

Roger (K8RI)


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