the swr problem is due the fact that these connectors are not made to
be 50 ohms at vhf frequency's..
I would think that the center tube is too big of a diameter.. but i
don't know much about these things..
your setup looks very nice too bad its not working as good as it looks..
other possibilities are find N bulkhead fittings... good luck.. i have
only seen thing a few inches long,,
or you could butcher a hole in the house and install a aluminum panel
or something.. get rid of the long bulk head fittings.. use something
like a UG-30D fitting..
http://cgi.ebay.com/05-01629-N-Female-Bulkhead-Coax-Adapter-UG-30D-U-RF-HP_W0QQitemZ7563908847QQihZ017QQcategoryZ1504QQtcZphotoQQcmdZViewItem
and get away from using anything other N connectors above 6 meters..
Ray J
W9RAY
k2kw-8@adelphia.net wrote:
> 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@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@comcast.net>
>> To: <vhfcontesting@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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>>
>
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