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

[wbr/wf4r]

Verrry intresting!  Tnx fer de feed back.   Glad you were able to find the 
problem. 73, Bill, WF4R

----- Original Message ----- 
From: <k8bb at comcast.net>
To: <k8bb at comcast.net>; <vhfcontesting at contesting.com>
Sent: Sunday, January 14, 2007 2:01 PM
Subject: Re: [VHFcontesting] impedence of 8" long bulkhead @ VHF/UHF?


> 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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