Dave Sublette wrote:
>
> Yes. I often find that the VF varies from published specs on RG-62 and
> other cables as well. I always cut[and] measure with an antenna
> analyzer or Grid dip meter to make [sure the phasing] lines or
> whatever I am making really do what want them to do.
> [early...not enough coffee]
> K4TO
>
> Steve Maki wrote:
>
>> My friend Eric K8LV seems unable to post to some of the reflectors
>> because of the new AOL front end he is using, so he asked me to relay
>> this. His e-mail address is evonvaltie@aol.com
>>
>> --
>> Steve K8LX
>> ********************************************************************
>> (fwd)
>>
>> I have discovered what may be a dirty little secret about RG62 coax.
>> While building up some transformers for a new phased array design, I
>> measured the VF of a brand new reel of ALPHA 9062 (RG62A/u) and found
>> it be about .725. This varies considerably from the mfrs. published
>> data, which specifies .82.
>>
>> Thinking that it was a defective reel, I then procurred a reel from
>> another mfr. (JSC) and lo-and-behold: the same result!.
>>
>> This much of an error in the VF, if not properly accounted for in
>> your design, can cause a considerable amount of reactance to
>> appear/disappear where not wanted. Since this is the only readily
>> available 90ohm coax available, it should be of interest to anyone
>> who works seriously with the design of antenna feedsystems.
>>
>> I would like to hear from anyone who has any knowledge relating to
>> this. I am attempting to contact the mfrs. for some input, but first
>> I have to penetrate their "tech support" firewalls (always a daunting
>> task.)
>>
>> K8LV Eric von Valtier
>>
>> ---
>>
>> Steve: (pse fwd to towertalk)
>>
>> I just broke on through to the other side - of the firewall at JSC
>> Cable. They admit that they have never actually measured and verified
>> the VF of RG62A/u, despite the fact that they have sold millions of
>> feet of it! The engineer that I spoke to is "looking into it" as we
>> speak.
>>
>> My educated opinion goes as follows. Several years ago mfrs. of RG62
>> changed the design of this cable, probably to allow use of a larger
>> center conductor. That would make it a lot friendlier to handle in a
>> world full of 75ohm cable and hardware.
>> In this new design the center conductor is smaller than the hole in
>> the dielectric and the difference in diameter is physically handled
>> by spirally wrapping a thread of dielectric around the center
>> conductor, which holds it centered in the dielectric.
>>
>> Now, however, the dielectric is not sold poly with an epsilon-sub-r
>> of 2+. But the people who wrote the catalog really don't know
>> anything about electronics, so they just used their old-wives wisdom:
>> e=2.3 so Z-zero is 93 ohms (based on the ratio of outer to inner
>> diameter, as usual.) Unfortunately, we have a situation here with a
>> sandwich dielectric where one layer is air with e=1.0.
>>
>> Worse, it appears that this discrepancy has been 100% duplicated by
>> every mfr. of RG62 that I am aware of.
>>
>> Finally, I would (as a reality check) appreciate independent
>> verification by anyone interested that VF=.73 +/- .1 for RG62.
>>
>> Eric
>>
>> List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
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>>
>> -----
>> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
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>> Problems: owner-towertalk@contesting.com
>>
>>
>
>
>
> List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
> Trylon Titan towers, coax, hardline and more. Also check out our self
> supporting towers up to 100 feet for under $1500!!
> http://www.anwireless.com
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
>
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
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