[Elecraft] High SWR problem

Sun Aug 17 16:26:05 2003

Edward:
  You don't give a lot of information to go on.  I gather your antenna is 
20 meters long.  Is it end fed or otherwise.  Supposing it is end fed, does 
that length include the feed line? or do you have a wire coming from your 
K2 that is 20 meters long total?  If the latter, that length wire is going 
to present a very high impedance on 40 meters (where it is a half wave) and 
above.  Perhaps the impedance is too high for your tuner to handle.

  Also, tuners, particularly in a situation like you describe, can be very 
touchy: the proper tuning point can be very, very sensitive -- and very 
easily missed.  I don't know if you have a good antenna analyzer, something 
like the MFJ 259, but such a unit is the easiest way to find your tunings.

  If you are unable to get an end fed 20 meter wire tuned, you might try 
something that is not resonant with a high impedance at the end.  A 40' or 
a 100' wire will often behave nicely.  Or, use the 20 meter wire with a 
feed line whose length you can vary.

  If you are using an end fed antenna, by the way, be sure to use an 
appropriate counterpoise to get maximum effectiveness from the antenna and 
maximum comfort in the shack -- you could otherwise end up with a lot of 
stray RF in the shack.

best wishes,

dave belsley, w1euy

--On Sunday, August 17, 2003 8:29 PM +0100 Edward Kenworthy 
<[email protected]> wrote:

> I'm a newbie, so please feel free to state the obvious :-)
>
> I've installed a 20m long-wire - on the basis that it was an easy way to
> get on the air. Problem is, I simply cannot reduce my SWR below
> "infinity" :-(
>
> I'm using a manual ATU and following the instructions I started at the
> suggested settings then adjust the transmitter and antenna knobs (I assume
> these are capacitances) with a fixed, recommended, inductance. But the SWR
> doesn't budge
>
> My house is a single storey and the longwire is attached at one end to the
> base bottom of the pole on which my VHF/UHF vertical is sited - so the
> long-wire is about 8' above the ground. It runs for about 5m near one side
> of the house (it's an L-shaped house) and by near I mean 1 foot or so
> away, and the far end is attached to a branch of an oak tree. Both ends
> are insulated and attached using some kevlar cord.
>
> My RF earth is a 4' copper rod wired to my ATU and transmitter using
> *braided* tinned copper wire.
>
> The ATU manual says, in essence, my RF earth is crap. 1 rod and using
> braided is bad idea it says. OK fair enough, but isn't the point of a long
> wire that it's easy - if I have to install an ultra-efficient earth system
> with multiple rods etc then that rather defeats the point.
>
> So, anyone have any suggestions ? Is it the location of the long wire (I'm
> wondering if running it near the house is the problem) or is it my rf
> earth ?
>
> If the latter - then is the long-wire a waste of time and should I just go
> for a dipole (I believe I don't need an RF earth for a dipole - is that
> right ?
>
> HELP!
>
> Edward
>
> _______________________________________________
> Elecraft mailing list: [email protected]
> You must be subscribed to post to the list.
> To subscribe or unsubscribe see:
> http://mailman.qth.net/mailman/listinfo/elecraft Elecraft Web Page:
> http://www.elecraft.com
> Also see: http://www.elecraft.com/elecraft_list_guidelines.htm

----------------------------------
David A. Belsley
Professor of Economics