Need Ideas for HF Antenna at Fire Station
 

A local fire dept will probably want regional communications within a
few hundred miles rather than DX and this would usually be on 80/60/40m
bands. Since the roof is metal, an ideal NVIS antenna for regional
communications would be a dipole type suspended 20-30ft above the metal
roof. To keep it simple, a T2FD type antenna would not require any
tuning or thought, just plug in and talk. B&W makes a commercial T2FD
style, model BWD-90. I know someone will chime in and say these are crap
but they work just fine and I believe a slight trade off in performance
for ease of use is paramount for the situation you describe.
Bob


Bob Dixon wrote:
Our local fire station would like us to provide an HF station to be
operated by hams during an emergencies. They have offered to pay the
cost of this. We already have an VHF station there. The problem is the
antenna. It cannot be visible (or at least not be at all obvious; they
are allowing the VHF antenna on the roof now.). The most likely needed
band is 75/80 meters, for in-state communications. So we need high-angle
radiation, and a vertical does not seem to be a good choice.

The roof is metal, so putting an antenna in the attic will not work.
The building is a fairly large 2 or 3 story structure, and in the
country with no other buildings nearby.

Here are some ideas I have:

1, A horizontal loop, running all around the building up near the top,
but somewhat below the metal roof. Would likely be non-resonant,
although perhaps we could choose the length. Mount it on stand-off
insulators just off the wooden siding. Use white insulated wire and
paint all hardware white, to blend in with the white siding. Feed it at
some convenient point, perhaps with a 4:1 balun and then coax into the
building. Open wire feed would be better, but we cannot get that into
the building and down to the station. Use a coax antenna tuner in the
station. The SWR would not be good, but the losses of RG/8 at 75M are
not that high. Maybe we could use some kind of outdoor automatic tuner
directly connected to the antenna, but I don't know of any offhand.

2. Use the rain gutters as an antenna. I did this long ago in a house
and it worked fairly well on 40M. Bridge all the joints with copper
braid, painted white, to endure reliable connections. At one of the
corner downspouts near the ground, connect the center conductor of a
coax cable to the downspout. Bury radials extending out from the
building an appropriate length, in a 270 degree sector, and connect to
the shield.
I don't know if the gutters are connected to the metal roof, but if so
that might or might not rule out this approach. Use a coax antenna
tuner in the station. I know this is basically a top-loaded vertical
antenna, but the choices are limited.

Comments on both these ideas, and other alternative suggestions, would
be greatly appreciated.

73,

Bob W8ERD

Need Ideas for HF Antenna at Fire Station
 

On Sat, 10 Feb 2007 08:35:55 -0800, Bob wrote:

To keep it simple, a T2FD type antenna would not require any
tuning or thought, just plug in and talk. B&W makes a commercial T2FD
style, model BWD-90. I know someone will chime in and say these are crap
but they work just fine and I believe a slight trade off in performance
for ease of use is paramount for the situation you describe.

Good morning, Bob.

Yeah, good luck with that.

T2FD antennas can exhibit as much as 17 db of loss while maintaining a
decent VSWR.

I have run communications tests with another amateur who lives one town
away. We have similar grounds, similar HAAT, and similar height AMSL. He
uses a B&W T2FD antenna (I believe it's the B&W-90) and I use a cut dipole
for 75 meters, at comparable heights (mine is 17 feet high and his is
something like 25 feet I think). He runs 100 watts and I run a grand
total of FIVE (5) watts with a Yaesu FT-817. I often get BETTER signal
reports on 75 meters than he does, from stations within about a 100 mile
radius of here.

I certainly wouldn't want a T2FD antenna for mission-critical use,
especially since for the price of a B&W, you could buy an auto-tuner from
LDG and have just about enough money left over to cover the materials for
a cut dipole.

Need Ideas for HF Antenna at Fire Station
 

The B&W BWD90 is about 5-6dB down from a dipole on 40m and up and 80m
and down does suffer more loss that’s true. If there is room for the
180ft version it should have consistent performance down to 80m. If you
try to feed a mono band dipole with coax and an LDG tuner it will
probably have more loss on some bands than a T2FD and using a 4:1 balun
and balanced line is better with an LDG but it will not tune everywhere.
What’s worse, an antenna that will not reliably tune where you need it
or an antenna that will always work with some loss? You have to consider
the user in this case as someone who may not have the experience to
diddle with tuners or recognize when something is not working properly.
Not everyone can make reliable contacts with an FT-817, it requires
knowledge, patience and higher efficiency antennas. If it were up to me
to set up a fire station for regional comms, I would consider the 180ft
B&W, a simple to use HF rig and a solid state 500w amp which will make
up for the 5-6dB loss of the antenna over a dipole when necessary. And
that is assuming a resonant dipole at low height is my design goal.
Also, 1000’s of B&W T2FD type antennas in use right now working just
fine in military and government use for there intended purpose, which is
push the button and get the message through without messing around.
Bob


Eric wrote:
On Sat, 10 Feb 2007 08:35:55 -0800, Bob wrote:

To keep it simple, a T2FD type antenna would not require any
tuning or thought, just plug in and talk. B&W makes a commercial T2FD
style, model BWD-90. I know someone will chime in and say these are crap
but they work just fine and I believe a slight trade off in performance
for ease of use is paramount for the situation you describe.

Good morning, Bob.

Yeah, good luck with that.

T2FD antennas can exhibit as much as 17 db of loss while maintaining a
decent VSWR.

I have run communications tests with another amateur who lives one town
away. We have similar grounds, similar HAAT, and similar height AMSL. He
uses a B&W T2FD antenna (I believe it's the B&W-90) and I use a cut dipole
for 75 meters, at comparable heights (mine is 17 feet high and his is
something like 25 feet I think). He runs 100 watts and I run a grand
total of FIVE (5) watts with a Yaesu FT-817. I often get BETTER signal
reports on 75 meters than he does, from stations within about a 100 mile
radius of here.

I certainly wouldn't want a T2FD antenna for mission-critical use,
especially since for the price of a B&W, you could buy an auto-tuner from
LDG and have just about enough money left over to cover the materials for
a cut dipole.

Need Ideas for HF Antenna at Fire Station
 

I remain puzzled why you guys are discussing compromise antennas in an
emergency communications system. I wonder if the fire department guys built a
compromise VHF/UHF communications system when they spec'd out their
requirements and performance. Did they hide their 154 MHz antennas under the
roof? Did they look for a means to "just get by?" Did they mount a rubber
ducky, with a gutter clip on the backside of the firehouse under the rain
gutter, and connect it with RG-58 to their radio?
If this is a for-real emergency communications solution that the community
desires, and they have asked amateur radio operators to be prepared (that is
truly an honor) then don't we hams owe it to the community and our own
reputation to build them a station, with antenna, that WORKS, that puts out a
solid, dependable signal?

Rick K2XT

Need Ideas for HF Antenna at Fire Station
 

After re-reading the original post I see the fire dept system will be
manned by experienced hams and that would allow for more complex but
efficient equipment like antenna tuners and antennas fed with balanced
line, etc. Even a G5RV with a tuner might be something to consider. One
thing I will point out would be the compromise if someone installed a
vertical like an R-7 or GAP Titan or Butternut, etc for regional or
statewide comms. The difference between a T2FD and resonant dipole would
seem like nothing compared to a T2FD over a vertical for this type use.
Bob


Rick wrote:
I remain puzzled why you guys are discussing compromise antennas in an
emergency communications system. I wonder if the fire department guys built a
compromise VHF/UHF communications system when they spec'd out their
requirements and performance. Did they hide their 154 MHz antennas under the
roof? Did they look for a means to "just get by?" Did they mount a rubber
ducky, with a gutter clip on the backside of the firehouse under the rain
gutter, and connect it with RG-58 to their radio?
If this is a for-real emergency communications solution that the community
desires, and they have asked amateur radio operators to be prepared (that is
truly an honor) then don't we hams owe it to the community and our own
reputation to build them a station, with antenna, that WORKS, that puts out a
solid, dependable signal?

Rick K2XT

Need Ideas for HF Antenna at Fire Station
 

On Sun, 11 Feb 2007 00:28:56 GMT, (Rick) wrote:

I remain puzzled why you guys are discussing compromise antennas in an
emergency communications system. I wonder if the fire department guys built a
compromise VHF/UHF communications system when they spec'd out their
requirements and performance. Did they hide their 154 MHz antennas under the
roof? Did they look for a means to "just get by?" Did they mount a rubber
ducky, with a gutter clip on the backside of the firehouse under the rain
gutter, and connect it with RG-58 to their radio?
If this is a for-real emergency communications solution that the community
desires, and they have asked amateur radio operators to be prepared (that is
truly an honor) then don't we hams owe it to the community and our own
reputation to build them a station, with antenna, that WORKS, that puts out a
solid, dependable signal?

Rick K2XT

I couldn't agree more. I suggest you go back to fire depatrment and
ask which they would rather have 1) an efficient and good working
communications system or 2) a small non-noticable antenna that
performs poorly. You can't give 'em both.

Danny, K6MHE

Need Ideas for HF Antenna at Fire Station
 

On Sat, 10 Feb 2007 18:50:54 +0000, Bob wrote:

If you
try to feed a mono band dipole with coax and an LDG tuner it will
probably have more loss on some bands than a T2FD

Good morning, Bob.

That's true, and that's why I wouldn't do that ... as you noted later, I'd
use ladder line and a balun.

What's worse, an antenna that will not reliably tune where you need it
or an antenna that will always work with some loss?

I don't know, depends on WHERE and to what extent the cut dipole would
fail to reliably tune. Anyway, that should be handled in the design of
the antenna, which of course needs to be done by somebody that knows what
he/she is doing. I assume that the fire department that is the subject of
this thread knows what frequency range(s) they need the HF station to
cover. Design the antenna and autotumer combination so that it tunes
efficiently across those frequency ranges

You have to consider
the user in this case as someone who may not have the experience to
diddle with tuners

That's why I suggest an autotuner.

or recognize when something is not working properly.

That's an issue with any installation. You could have any antenna you can
imagine, and something could go wrong making it "not work properly".
There needs to be someone around who has the skills and experience to
recognize that.

If it were up to me
to set up a fire station for regional comms, I would consider the 180ft
B&W, a simple to use HF rig and a solid state 500w amp which will make
up for the 5-6dB loss of the antenna over a dipole when necessary.

What if your emergency installation has to operate for extended periods of
time on emergency power and you need to conserve power? That power-hungry
500-watt amplifier may not be especially welcome in that case.

Anyway, I could put up at least three (or more) cut dipoles with ladder
line and autotuners for the price of that amplifier.

Also, 1000's of B&W T2FD type antennas in use right now working just
fine in military and government use for there intended purpose, which is
push the button and get the message through without messing around.

They are working, somewhat, for the most part. I would argue whether
they're working "just fine". They're doing the job because (a) the people
that installed and use them don't know the difference; and/or (b) they
have plenty of your tax dollars to spend on higher-power transmitters to
compensate for the antenna inefficiency; and/or (c) they're operating ALE
installations that jump around all over the spectrum and, really, the T2FD
antennas are all they can use so they have to suck it up and live with the
loss.

Need Ideas for HF Antenna at Fire Station
 

On Sun, 11 Feb 2007 03:01:13 +0000, Bob wrote:

Even a G5RV with a tuner might be something to consider.

One thing you need to keep in mind is whether even 75 meters will be
sufficient for statewide communications around the clock. I can tell you
that often it is not. Around here, in the wintertime the critical
frequency (the maximum frequency at which a signal arriving straight up
will bounce back) falls to well below the 80 meter band at night. Often
the critical frequency will be around 2.5 MHz, or lower, by around 10 PM.
During those times, your 75-meter NVIS signal will just go sailing off
merrily into space. You have to be on 160 meters during those times, if
you want reliable NVIS communications.

I am a regular participant in a military traffic net (not MARS, but
similar) that operates at 0730 each morning, on a frequency that's not so
very far off the high end of the 75-meter band. The normal net control
station is about 80 miles from here, and in the wintertime, the critical
frequency is often right around our operating frequency and rising fast as
the sun comes up. Very often, I can just barely hear the NCS (or can't
hear it at all) at net starting time of 0730, but by 0745 to 0800 the NCS
has come up in strength to where solid 100 percent copy is easy. Move the
net start time to a half hour earlier and there'd be no way... we'd all be
talking to ourselves.

As for later in the daylight hours, 75 meter signals often get absorbed by
the D and E layers so they never bounce back. During those times 40
meters is your only hope.

So, for an emergency station that has a snowball's chance of being able to
maintain communications 24x7, you need 160, 80, and 40 meter coverage from
an antenna around 30 feet high if you can get it up that high. That would
be the low end of the best height range for 160 meters and the high end of
the best height range for 40 meters.

Need Ideas for HF Antenna at Fire Station
 

I use a version of a fan dipole on HF.

It differs from the standard fan in that the wires are hanging under each
other with the longest wire on top. There separated 12" apart, the first one
being close to the feed point.
The 3 wires are cut for 20m 40m and 80m. With a good tuner it will tune any
band from 10m and even a bit of 160m close to 1.8mhz.

One good thing about it is...

After it was tuned, I measured everything. If a storm or such takes it down
it can be replaced very quickly.
It is also hard to see unless you are looking for it.

My 2 cents
KI4ILB solar powered ham radio 24/7

Need Ideas for HF Antenna at Fire Station
 

Dear Bob:

It is nice to hear from another of W8JK's boys.

You have received some good ideas and discussion.

Having dealt with the underlining need you described, the technical
issues usually turn out to be minor as compared to the people issues. What
you are likely most to need is a sharp people-person who can uncover what
the real reasons are for the apparent need for invisibility. Once you know
what the actual issue is, you can work to optimize the system.

You must have the clout, once you understand the people issues, to
convince the right people about an effective antenna system.

My preference is a dipole with about 100 feet of wire on each side that
is supported in the middle by a 40 foot tower. From the feed point to the
base of the tower I would run a piece of solid-outer coax that is heavily
choked with surrounding choking-material. At the base, I would attach a
commercial auto-tuner and run its coax and control cables (well choked)
underground to the station. An embellishment would be a second dipole at
right angles (connected to the first dipole) that is resonant around 5.4
MHz. A good fence around the tower is desirable.

Feel free to contact me.

73 Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
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