Dick,
I personally like OPTION 1.
If you can insulate the base of the antenna from ground for the power you
plan to use.
The end of the antenna will be at a high voltage point as the half wave for
forty.
I would set the vertical up a little short for 80 meter operation. Add a
small amount of base loading so a good match can be made for Phone or CW
operation. You could do this with a single relay.
For 40 meters use a parallel-tuned network at the base of the vertical.
ON4UN covers this in his Low Band DXing Handbooks under the Vertical Dipole
section.
The values for 40 meter operation he gives are:
40 pF
13 uH
It sounds more complicated then it really is. Remember to disconnect the
tuning unit you are not using. If you go with two coax lines, which is the
simplest, connect the unused end to ground when not in use. Also run a few
1/4 wave radials for EACH BAND. This should help stabilize the matching.
P.S. I ran a Half Wave wire vertical for 160 Meters using this
parallel-tuned system with a six foot helium balloon. Worked great!
Best of luck,
Rick AA2MF
----- Original Message -----
From: <RLVZ@aol.com>
To: <towertalk@contesting.com>
Sent: Friday, September 05, 2003 3:53 PM
Subject: [TowerTalk] 80 - 40 Meter Vertical Ideas
> Hi guys,
>
> I plan to homebrew a combination 80-40 meter vertical to place at the edge
of
> a saltwater river. I am thinking of using one of the following options.
> Your thoughts would be greatly appreciated.
>
> OPTION 1: Use a 33' tower and extend a 33' length of aluminum tubing out
of
> the top section giving a combined height of aprx. 66'. I could insulate
the
> tower from ground and base feed it giving me a 1/4 wave on 80 and a 1/2
wave on
> 40. I would then need to match the base impedence for 40 meters. What
would
> you recommend for matching the impedence?
>
> OPTION 2: Use the same 66' structure as listed in Option 1 but ground
mount
> the tower. Have 2 shunt feed systems: one for 40 and one for 80. Can I
have 2
> shunt feed connected at the same time?
>
> OPTION 3: Use the same 66' structure as in Option 1 but not only insulate
the
> tower from ground but isolate the top 32' section from the bottom. This
> would give me a 1/2 wave vertical dipole on 40. When used for 80 meters I
would
> use a relay to connect the lower and upper halves giving me a 1/4 on 80.
What
> would you recommend I use to switch in/out the two sections?
>
> Ideally, I would like it set up for fast band changes. (no time to fool
> around outside during a contest!)
>
> Any recommendations at to which option would provide the best field
strength,
> bandwidth, easiest match, etc. etc. etc. is much appreciated!
>
> 73, Dick- K9OM
> _______________________________________________
>
> 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.
>
> _______________________________________________
> TowerTalk mailing list
> 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.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|