[Antennas] Verticals, <2/1 VSWR bandwidth?

Sun Jul 17 17:37:24 EDT 2005

Dear Phil,
> My Roof mounted (over about 1200 Sq/ft of sheetmetal roof) Hustler 6BTV
> vertical has the following bandwidths of less than 2/1 SWR. . .
>> 40 Meters is 230KC wide, centered at 7120KC.
> 75 Meters is 48KC wide, centered at 3730KC.
> It dips to a nice low 1.1/1 at resonance.
>> My desires are to improve the overall antenna system here with separate
> verticals for the low bands and high bands and add inverted Vees for 20, 15 &
> 10 meters to augment the high band vertical. (I'm trying to minimize traps on
> the low band antennas).
>> Late this fall I plan on replacing the Hustler 6BTV antenna with a Butternut
> HF-2V vertical, set up for 80/40 meters only (no 30 or 160). Although the
> Hustler is working well with no radials, I expect to put a number of radials
> for 40M under the HF-2V, there is NO room to put out 80 Meter radials, though
> I expect that the sheetmetal roof will provide sufficient groundplane (better
> than nothing, like a BIG MOBIL setup ;-)
>> Questions:
> 1. I would expect that I would get a wider usable bandwidth on both bands,
> SWR wise. Anyone have any idea what bandwidths I can expect on this antenna
> (SWR <2/1)?

Perhaps I'm missing something, but typically the lowering of losses (more
radials) results in higher Q and smaller bandwidth.
> 2. Since the HF-2V is a full sized vertical on 40M, I would expect that it
> would outperform the Hustler with traps. Thoughts?

Almost anything will be better than traps - for a variety of reasons.
> 3. Though they would be short, would those 40M radials help any on 75M. This
> may be a myth, but somewhere I read that a gazillion short radials of 20 feet
> or so were more effective than just a few longer ones? Remember this will be
> over a sheetmetal roof that is already part of the antenna ground system.

You may want to consider that your "radials" are more like a counterpoise - in
which case I believe they need to be tuned properly in order to be effective
> 4. Does that Butternut "TLK" top loading device really improve the bandwidth
> of the antenna, by how much? The Butternut site doesn't say a whole lot about
> it.
>> 5. Finally, should I just lay the radials on the metal roof, or would it be
> better to tie them off in the corners of the mobile home so that they are
> lifted (very) slightly above the roof?

It's difficult to imagine that just lying on the roof would offer anything at
all. Isn't the roof acting as a ground plane?
Bob Lay (W9DMK), Dahlgren, VA
w9dmk at crosslink.net
http://www.qsl.net/w9dmk