[Elecraft] High SWR problem

Sun Aug 17 16:46:00 2003

On 17/8/03 9:21 pm, "David A. Belsley" <[email protected]> wrote:

> 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.
> 

It's end fed (is there anyother way to feed a longwire ?) and it's 20m long
plus it's fed by some low-loss coax (with a balun).

> 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.
>

Don't have one and am not sure if the club has either so for the moment
that's not an option.

> 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.
>
OK.

> 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.
>

Counterpoise == rf earth ?

> best wishes,
> 
> dave belsley, w1euy
>

Thanks :-) Edward

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