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

[k2kw-8 at adelphia.net]

Any speculation on the cause of the SWR problems?  Could the metal used be a problem?  E.g. stainless steel is used in many antennas (and touted for it's strength), but it's a horrible conductor and is worthless IMHO for antennas.

Kenny K2KW


---- k8bb at comcast.net wrote: 
> Well, here is the conclusion: The bulkhead connector(s) I am using are
> causing the SWR problems at VHF and UHF.
> 
> While visiting his QTH this past weekend, Tim Duffy, K3LR, was kind enough
> to check an assembly (bulkhead-jumper-bulkhead) on an HP Network Analyzer.
> Sure enough, the bulkhead connector(s) do not behave above HF. At 10m and
> below, they exhibited good impedance and SWR. However, above 30MHz, the
> bulkhead connectors were unstable and clearly were the cause of my weird SWR
> readings. The 10" connector was worse than the 4" connector, but both were
> totally unacceptable. (The jumper itself was fine.)
> 
> Next, I cut one open. I was pleasantly surprised to find them "physically
> competent" ... I think. While I was not sure what to expect, this is what I
> found:
> - The center conductor is a heavy-duty, solid rod stock and consistent
> throughout the entire length of the 10" bulkhead - no thin wire or coil
> spring. (I once had a bad experience with a 90degree connector.)
> - The "dielectric" was present only at each end of the connector, where the
> center pin was received at each end - it was air dielectric throughout the
> entire middle.
> 
> I have no question that these will be fine (reliable) at HF with 1500 watts.
> 
> Thanks to the many responses I received from this list. Each part helps to
> put together the whole in understanding the solution when troubleshooting a
> problem. Special thanks to Tim Duffy for his time and attention and to the
> other individuals who offered to do the same.
> 
> I took some digital photos of the cut-open connector that can be see at:
> http://home.comcast.net/~k8bb/bulkhead.htm
> 
> 73!
> Don Chisholm
> K8BB
> 
> ----- Original Message ----- 
> From: <k8bb at comcast.net>
> To: <vhfcontesting at contesting.com>
> Sent: Monday, January 01, 2007 23:13
> Subject: [VHFcontesting] impedance of 8" long bulkhead @ VHF/UHF?
> 
> 
> > 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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