[VHFcontesting] impedence of 8" long bulkhead @ VHF/UHF?

[k2kw-8 at adelphia.net]

I have even seen SWR changes and velocity factor changes at HF with non-Amphenol short barrel connectors, PL259's, T-connectors, and push-on PL259 connectors. 

I've made a lot of coax stubs for HF contest interference, and a crud connector can change the effective coax required by a few feet, even at low frequencies.  It's amazing the impact on velocity factor some of these connectors can have.

As a result, I have hoarded Amphenol UHF barrel, T, right angle connectors, and 4" bulkhead connectors when I can find them.  I haven't seen 8" Amphenol, but then again, I haven't needed them in the past.

73 & GL.  Kenny K2KW






---- k8bb at comcast.net wrote: 
> Hello,
> 
> I have searched the archives for this, but I do not see an answer.
> 
> My Question:
> What is the reason that I show *very weird* SWR curves at VHF/UHF when
> feeding through UHF bulkhead connectors that are 8" ( and/or 4") long when
> measured into a known 50 Ohm load good through VHF.
> 
> My Situation:
> My feedlines enter my house/shack through two bulkhead "panels" connected
> with 9913 equiv. between. You can see pictures and a "story" at this web
> page http://home.comcast.net/~k8bb/ant.htm which explains why I have this
> arrangement and how I went about installing it. Through process of
> elimination, I have determined that somewhere between the shack panel and
> the outside panel there is occurring what I think is some sort of impedance
> mismatch that is causing high and very inconsistent SWR at VHF and above.
> 
> My Suspicion:
> I think that the bulkhead connectors that are feeding through the panels
> (probably the 8" ones?) are not a consistent 50 Ohms throughout and are
> causing enough of a "bump" in the system impedance to cause bad SWR readings
> on 2m and 70cm. The 4" (UG-363/4INCH) and 8" (UG-363/8INCH) bulkheads were
> purchased through The RF Connection: http://www.therfc.com/uhf.htm
> 
> Maybe Not The Coax?:
> The coax that connects them is 9913 equivalent (JSC Wire and Cable Type
> #3500) from a local CB shop. It is not exactly Belden or Times, but I have a
> lot of experience with coax and connectors and the stuff "looked and felt"
> quite good. (In high school, I worked in a local CB/HAM shop and installed
> HUNDREDS of PL-259 connectors on countless types of coaxial cable. I
> developed a pretty good sense of what good cable and good connectors were
> all about. The connectors are all Amphenol with Teflon.)
> 
> Eh? Ideas? Suggestions?
> 
> Thanks for reading ... Happy New Year
> 
> Don Chisholm K8BB
> Pontiac, MI
> 
> 
> 
> 
> 
> 
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