The problem is most acute when the length of the coax transforms the
off-resonance feedpoint impedance to a low resistive value - for example
around 6 Ohms for 45ft of Rg-8X; the tuner then doesn't have enough
shunt capacitance to provide a match - about 2500pF would be needed. In
those situations - as Rick says - extra external capacitance would help.
Steve G3TXQ
On 08/07/2013 23:14, Rick - DJ0IP / NJ0IP wrote:
You should be able to match it by adding additional capacitance to the rear
of the 238.
Like Jim, I always cut mine to about 3600 and have no trouble matching it
across the upper portion of the band with the 238B.
I've never tried to cut it high and match it lower.
If it doesn't match, add about 17 to 20 ft. of coax and then it most likely
will.
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Steve Hunt
Sent: Monday, July 08, 2013 11:56 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Tuner
At 3.5MHz, the SWR(50) of an 80m dipole cut for resonance at 3.8MHz could
easily be 12:1 or higher. Depending on the length of the coax, that can
present impedances at the tuner that will be well outside the matching range
of a 238.
Steve G3TXQ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|