[Elecraft] NOT the feedline (was KPA-1500 faulting on 6m; SWR issues)

[Peter Dougherty]

The new full-length LMR-400 cable is about 3 feet longer than the old 2-section coax I had before (old = 3/8” hardline and about 8 feet of RG-213). The entry point is grounded to rod immediately below it, connected by 1.5” braid. 

 

- pjd

 

From: Mark Goldberg <marklgoldberg at gmail.com> 
Sent: Monday, June 1, 2020 12:45 AM
To: Peter Dougherty <lists at w2irt.net>
Cc: Adrian <vk4tux at gmail.com>; Paul Baldock <paul at paulbaldock.com>; Elecraft Mailing List <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] NOT the feedline (was KPA-1500 faulting on 6m; SWR issues)

 

I haven't seen a discussion of your grounding system or feedline length. 6M can be picky.  What does your ground system look like? Do you have any common mode chokes on the feedline? Have you tried adding or subtracting 2-3 feet from the feedline? If it is exactly a multiple of 1/2 wave or 1/4 wave changing the feedline length will move it away from that. Have you tried adding a counterpoise in the shack? That's not the ultimate solution but if it improves things it will tell you something. Can you point an IR thermometer at tuner / balun inductors to see if they are getting hot? Just throwing out ideas.

 

73,

 

Mark

W7MLG

 

 

On Sun, May 31, 2020 at 9:08 PM Peter Dougherty <lists at w2irt.net <mailto:lists at w2irt.net> > wrote:

New coax and old coax behaved identically. HOWEVER, running into about 80 feet of old RG-213 and into the Cantenna dummy load and it doesn't fault. This is the only condition on 6m where there is no fault. Brand new coax, old coax, brand new antenna, old antenna, with balun, without balun. Always faults except when feeding the pure resistive dummy load. If there's any reactance it trips or gives false SWR info.

I would also add, why would a 2:1 SWR trip out the amp at 25 or 30 Watts of drive? On the regular HF bands I can use the internal tuner to take out a 2.5 or 3:1 SWR and it still sends 1400-1450 Watts up the pipe..

 - pjd