----- Original Message -----
From: <billmilosz@aol.com>
To: <towertalk@contesting.com>
Sent: Wednesday, April 20, 2005 10:23 AM
Subject: Re: [TowerTalk] 1 5/8" hardline to N female?
> Sorry, I guess I didn't give enough info.
>
> This antenna is a Harris Skytiller SKH tuned to 106.7 MHz donated to a
nonprofit group for use in LPFM service. This is a commerical
circularly-polarized VHF antenna. Installation details of the 10-watt
xmitter reqires use of very flexible cable, hence some kind of RG-8X must be
employed. (Besides it's not really necessary to use 1 5/8 hardline at 10
watts.... though I'm sure the loss would be low, LOL) Hence, the need for
N-to-1 5/8 adapter, and the volunteer / nonprofit nature of the project
prohibits spending $200 for a commerical adpater.
>
> SWR measurements were made with an MFJ-259B at the resonant frequency of
106.7, in addition I swept up and down and indeed it does reach a minima
around 106.7- although the slope to the minima is a gentle one. I also
tried the transmitter and a decent quality directional power meter just in
case my MFJ-259B was malfunctioning, but the results agreed between the two
methods- SWR greater than 5:1
How did you connect the MFJ-259 to the antenna? Did you have a borrowed
adapter?
Here's some suggestions on improvising an adapter..
Use a tapered transmission line section. Make two cones out of copper sheet
to transition from the big connector to the appropriate diameters for your N
connector (or TNC, for that matter). Ideally, it would have exponential
tapers, but fabrication might be a "challenge".
What about open wire line approach? Or, simulated cone transition with,
say, 2 or 4 wires for outer conductor and same for inner conductor.
A somewhat fancier way would be to make a step transition to the bigger OD,
and then use tapered dielectric to adjust the average epsilon within the
space between outer and inner.
Try a "step" transition. Your transition is short, maybe the mismatch won't
be intolerable? Maybe a series of 2 or 3 steps? Think about it.. a N
connector on RG-174 has a pretty big difference in conductor diameters, and
doesn't have a huge mismatch. (although, some of the "mounting adapters" to
put tiny coax into big connectors have tapered components, so maybe that's
how they do the matching)
Looking at some of the pictures at:
http://www.surplussales.com/Connectors/EIA-6.html it seems that steps aren't
all that unusual That 3-1/8 to 1-5/8 adapter looks pretty short to not be a
sudden step.
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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