> Mike - You have already received some good advice on your 5BTV
> installation. Let me add my bits of advice.
>
> 1. If you use a lot of radials in an elevated installation, they don't
> need to be resonant. The purpose of the radials is to provide a return
> current for the transmitter and screen the antenna from the ground (in
> your case the roof and house) to reduce losses. So I suggest that you
> start with 16 or more radials the height of the vertical. A conventional
> ground plane antenna does not really act like a ground plane antenna
> unless it is fairly high above the ground.
>
> 2. A choke balun at the antenna feedpoint, one where it exits the radial
> field, and one at or near the transmitter should help keep the common
> mode currents down. A good choke balun can be made by winding as many
> turns of the feedline around a FT240-433 or -61 ferrite core as you can
> manage. There are other solutions that will work, such as ferrite beads
> or an air core balun, but the ferrite toroid is simple and effective.
>
> 3. Some commercial verticals are "DC grounded" by design with an RF choke
> across the feedpoint. Check to see if the 5BTV is by using an Ohm meter
> across the coax connector. If you get continuity you are probably OK. If
> you can add such a choke use 2 to 3 microHenrys. If this is the case, you
> are in good shape, add a lightning protector, like the Polyphaser or ICE
> where the coax enters the house and install a good ground. This is a good
> place to add the choke balun, put it after the lightning protector.
>
> 4. The admonition against the tuner is to prevent you from using the
> antenna when it is not functioning properly or from using it on a band
> for which it is not intended. Using it within the band is OK.
>
> 5.Moxon's concerns about quarter wave radials stem from two points.
>
> a. If the quarter wave length radials are not exactly the same, then
> there can be considerable disparities in the current each radial carries,
> along with high angle horizontal radiation and reduced radial efficiency.
> Shorter or longer radials share currently more evenly even if they are
> not exactly matched in length. Longer radials can be tuned to resonance
> with a series capacitor.
>
> b. Quarter wave radials are more likely to couple to the feed line
> causing common mode currents on the outside of the coax. Using a choke
> balun at several points on the feedline, as indicated above, will help.
>
> You will avoid problems in radials by increasing the number of radials
> you use. This will reduce the magnitude of current in each radial and
> spread the current over a greater area, both important factors in
> reducing ground losses and increasing efficiency.
>
> 6. Don't expect very good performance on 80M. The antenna is short and
> you are unlikely to be able to put in a good enough ground system to make
> it very efficient. Still, it is better than no antenna.
>
> 7. DX Engineering has a 5BTV manual on their website that may have more
> information on it than you currently have. Check it out.
>
> Let us know how it all works out. - Dr. Megacycle KK6MC/5
>
>
> _______________________________________________
> Elecraft mailing list
> Post to:
[hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>
http://mailman.qth.net/mailman/listinfo/elecraft> Help:
http://mailman.qth.net/subscribers.htm> Elecraft web page:
http://www.elecraft.com
Subscriber Info (Addr. Change, sub, unsub etc.):