[TowerTalk] HF2V Elevated or On Ground
grants2 at pacbell.net
Thu Nov 14 11:54:32 EST 2013
A very interesting question. I've had two verticals on metal roofs but
the roofs were galvanized steel over wood frame. Thus the roof acted as
an elevated ground plane. One worked very well for me with an 80m top
loaded vertical on a barn about the size and geometry of your building.
This insulated roof structure can be analyzed with EZNEC.
Now, I have an all metal building 56 x 70' which is a very tempting
target for an elevated vertical. However, the metal walls are connected
to Ufer grounds in the footings, which goes against the (correct I
believe) advice to not ground an elevated set of radials. I know EZNEC+
5 can't analyze this, maybe something else can. Advice?
I've gotten advice to use tuned insulated radials suspended a foot above
the roof. Makes some sense, since the ground loss from the roof will be
quite low. However, with the coupling I wonder if they can be
"tuned". I just added an 8th elevated 120' radial to my 160m T and got
a bit of surprise in how much the swr changed, I think because of
coupling to the steel building. Radials 6 & 7 are farther away and had
little influence on swr & resonance as they were added.
OTOH, if you think about elevated radials, at some number (above 4 or so
I think) the concept of tuning them makes no sense. Extrapolating to
large numbers of radials and then to a uniform sheet conductor, is like
asking "what is the resonance of a perfect ground plane?" N6LF's
extensive QEX, QST, & his web site elevated radial analysis shows this
property. With enough (8 or more) elevated radials, the length can vary
quite a bit without much change in performance. The goal is to shield
the lossy earth from the field.
So another thought experiment is to start with your roof on the ground.
Would you not use it as a ground plane? Of course not, but you might
add some wire radial extensions if the metal area was small. Now start
raising the roof, and in an all metal building, keep it electrically
connected all around to earth. Would antenna performance degrade? If
so, at what height and why is the *really* hard question? Or imagine a
fantasy, a vertical on top of a bump of salt water. Or if the earth
around the building was covered with steel.
So, IMO verticals on metal roofs as a ground plane are excellent low
angle radiators if the dimensions of the roof are significant e.g. ~1/4
wl. There are also the advantages of fewer objects to interact with the
near field and the slope of the roof improving the match as it does for
VHF ground plane verticals.
With a SPDT relay, it wouldn't be too difficult to try a real time 4
"tuned" elevated radials over the roof vs direct roof connection say for
20m. I've not seen anything published, anybody have any links?
On 11/14/2013 5:51 AM, Patrick Greenlee wrote:
> I have a Hy-Gain Hy-Tower on top of an all metal barn. Base is about
> 23 ft AGL. I have no radials. It works pretty well. I got a
> recommendation to put at least 4 radials on the roof (2.5:12 pitch
> gable roof) and preferably 4 cut for each band that can stay on the
> roof (roof is about 38x74 feet and ant is dead center.) Thoughts?
> Patrick AF5CK
> -----Original Message----- From: GARY HUBER
> Sent: Wednesday, November 13, 2013 10:59 PM
> To: Michael Murphy ; TT TowerTalk
> Subject: Re: [TowerTalk] HF2V Elevated or On Ground
> Mike, I forgot to say the top loading can give your HF-2V a low VSWR
> the entire 40 M band or across the entire phone or CW portion....
> great for
> 73 ES DX,
> Gary -- AB9M
> -----Original Message----- From: Michael Murphy
> Sent: Wednesday, November 13, 2013 9:25 PM
> To: Mike & Coreen Smith VE9AA
> Cc: towertalk at contesting.com
> Subject: Re: [TowerTalk] HF2V Elevated or On Ground
> I have an HF-2V ground mounted with 32 - 40 foot radials under it.
> When I
> went from 16 to 32 radials, 80 became significantly more touchy to tune.
> That said, it works very well on 40 and 80 into EU.
> This weekend I plan to add 4 -12 foot wires for a top hat for 80.
> According to Bencher, it will improve performance on 80 as well as a
> little more bandwidth. Anyone tried this?
> Mike - KI8R
> On Wed, Nov 13, 2013 at 6:51 PM, Mike & Coreen Smith VE9AA <
> ve9aa at nbnet.nb.ca> wrote:
>> I recently installed an HF9V at around 8' AGL. I use 2 elevated
>> "ground"(counterpoise) radials per band, sloping from 8' down to
>> about 5'
>> I find it works VERY well on 40m and up and adequate on 80m.
>> Over the past month, I've compared it to a host of other wire
>> antennas at
>> similar heights and always found the Butternut to be as good or better
>> than anything else in the yard here. I believe the raised radials have
>> loss, but it was twitchy to tune. An HF2V ought to be a cake-walk to
>> It's just my opinion that using only a few ground radials is lossy and
>> that's why everyone preaches ground mounting it. (a lot easier to
>> tune w/
>> better/wide 2:1 SWR curves) (I use the term "better", but I don't really
>> mean better, but it is better for the match, but I think it's like
>> power into the ground to heat worms.)
>> So far I have around 2500 Q's with it, contesting every weekend and I am
>> sure it works well , raised up like it is.
>> p.s.- subscribe to the Yahoo group for Butternut antennas and then check
>> files section for "VE9AA" or "AD5X".a couple good ideas
>> how to get the whole 80m band out of the antenna.
>> 73 Mike VE9AA, NB
>> TowerTalk mailing list
>> TowerTalk at contesting.com
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