[Antennas] increased antenna bandwidths through a tuner, why?

Sat Apr 29 08:56:46 EDT 2006

SWR can be a complicated thing; you may be thinking only resistance (50ohms)
but you are forgetting the reactance factor. Capactive or Inductive
reactance can take a 50ohm resistance and give it a 2:1 or worse SWR...
Now in your case, I suspect the tuner may be throwing enough reactance in
the opposite directions to cancel or smooth out the curve on the
antenna...thus allowing you to see a broader SWR curve...does the antenna
radiate any better? Probably not....you are tuning the coax and antenna in
this case...and the radio will "see" a lower SWR...but you havent done
anything to make the ANTENNA radiate better (a falicy of an antenna
tuner..it doesn't tune the antenna, It tunes the coax!) You merely have
allowed the radio to put out more power into the coax because the radio sees
a lower SWR and that MAY help your signal on the air (but unless you are
getting more than 3-6db increase, is it really worth it)...
The antenna tuner NEEDs to be at the base of the antenna and remotely
tunable to get the BEST overall performance of your antenna.
Chris
WB5ITT
> -----Original Message-----
> From: antennas-bounces at mailman.qth.net 
> [mailto:antennas-bounces at mailman.qth.net] On Behalf Of Sam Morgan
> Sent: Saturday, April 29, 2006 7:27 AM
> To: antennas - qth.net
> Subject: [Antennas] increased antenna bandwidths through a tuner, why?
>> I have a bugcatcher set with 1:1 at center frequency of 7.09 
> with no tuner.
> It has a base coil taped for minimum swr.
>> When I check the 2:1 to 2:1 bandwidth it is about 76kc.
>> If I run it through my home brew T-tuner, and set the tuner 
> to have the same 1:1 at that same 7.09 frequency, I then get 
> a bandwidth of 151kc. (not touching up the tuner further than 
> when I set it to 1:1 initially).
>> The tuner is set with both caps @ 50% and the (small) roller 
> inductor is set at about 7 of 17 turns out from minimum inductance.
>> It makes me happy, sure, but I'm wondering if someone would 
> explain it to me.
> How does it increase the bandwidth if the same 50ohm feed 
> point is there with or with out the tuner.
> --
> GB & 73's
> KA5OAI
> Sam Morgan