Topband: Shunt feeding the Skyneedle - new developments

[Carl Braun]

Tom

I assume the system has reactance since the MFJ is reading the "X" and I'm seeing the resulting SWR on the analyzer AND at the rig.

The swr at my given freq as tuned with the variable cap is 1.3:1 or less...outside the enclosure the system had 1.0:1 swr readings and X=O over what appeared to be a broader bandwidth...even with 42 ohms at the feed point. 

I'm having fun in the contest and the antenna seems to be transmitting well and the amp hasn't blown up yet.  I have a very short run of RG58 from the panel to my switching network so I'm keeping the amplifier below 500W.

I'm definitely ready to get the RX loop up as listening on the needle is rough.

Thanks Tom

Carl AG6X

-----Original Message-----
From: Tom W8JI [mailto:w8ji at w8ji.com] 
Sent: Saturday, February 22, 2014 12:17 AM
To: Carl Braun
Cc: 160
Subject: Re: Topband: Shunt feeding the Skyneedle - new developments

The j11 ohms is the best I can get period. I was able to get j0 when the cap 
was outside of the steel enclosure with a better bandwidth. Maybe I should 
throw my $400 enclosure and find a fibergla$$ enclosure. But as others have 
indicated I should probably just live with it.>>>

1.) How do you know the system really has some reactance?

2.) What is the SWR, that is more accurate.

3.) The SWR is meaningless anyway for control settings when  it is below 
maybe 1.3, and is typically meaningless for system losses when below 4.0:1 
for short cables on 160 meters. A 40 j10 load (if it is that) is around 
1.3:1, so it falls in the meaningless category


Do you think a smaller (physically) vacuum cap would have less interaction 
with the steel enclosure.  The one I have is only 3" round and 6" long. The 
air variable I'm using is 13" long and 7" round at mesh>>>>

RF behavior with chassis and cabinets and wiring can be complicated. Some 
people who work around it all their life never actually get a feel for how 
simple systems work, let alone things that might get colex like high 
impedance lines and physically large components inside close spaced boxes.

The interaction depends on the circuit impedance and the impedance of any 
components and wiring at various points in the system inside the box. You'll 
probably never get a meaningful answer because the problem is small, an 
answer requires knowing the actual impedances of everything, and at a 
minimum a feel for how the box and wiring *you* have interacts with the 
impedances.

The important thing at this point is how the equipment in the shack behaves 
with what you have, because any actual losses are meaningless.

73 Tom