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@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
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|