David G. Nagel wrote:
Rick (W-A-one-R-K-T) wrote:
I'm quite active in CAP and MARS and so I need to be able to operate on a
fairly long list of frequencies between about 2.2 MHz and about 27 MHz
(actually up to 24 MHz would probably be OK, not much goes on above
there).
I'm looking for the best compromise antenna that will get me most of
those
frequencies with reasonable receive performance without a tuner, and SWRs
under about 3:1 that my FT-1000's internal tuner can handle.
The plan is to program the frequencies of interest into my rig's memories
and then scan across them, hence the need for reasonable receive
performance with the tuner out of the circuit.
I'm aware of the B&W "radiating dummy load" (TTFD) antennas but I'm not
quite ready to give up that much efficiency and I'm DEFINITELY not ready
to blow $300 on one.
I don't mind putting up a multi-legged dipole array but I don't want
to go
overboard, and from my calculations (such as they are), I'd need a total
of SIX (6!!!) dipoles all fed with a common feedline and operating on
their fundamentals and third or fifth harmonics in order to stand any
chance at all of covering it all.
I was thinking of maybe something like some variation of the G5RV, or the
W5GI "Mystery Antenna" (http://www.w5gi.com), cut to an appropriate
center
frequency above or below the 20 meter band as needed, then maybe
(MAYbe) I
could get away with three of them.
Any thoughts?
Rick;
Don't sell the B&W antenna short. It is more than sufficient for most
CAP/MARS/Amateur communications. When configured as a NVIS antenna you
can reach almost everyone in your region. I have worked a distance
sufficient to cover the upper portion of the US east of the Mississippi.
Yes the efficiency of the B&W is not on a par with a tuned dipole
antenna but it offers the flexibility to cover all the CAP/MARS/Amateur
frequencies with out having to resort to an antenna tuner. Even then the
relative efficiency of the B&W when compared to an out of resonate
dipole is more than enough to compensate. This is why CAP/MARS/DOD use
the B&W for ALE communications.
Can't beat instanteous good enough match.. and the loss is on the order
of 6dB (see Cebik's webpage on T2FDs). pretty darn simple and screwup
proof.
If you insist in not using the B&W then a fan array of dipoles cut for
your frequencies of choice can be used. There is some interaction
some interaction? You're going to go insane trying to tune this,
particularly in a field installation if there's any wind blowing to
change the relative positions of the wires and any surrounding stuff. 3
wires works ok to cover 10,15,20,40 and can be tuned reasonably well in
10-15 minutes if you have some sort of antenna analyzer that lets you
sweep it to find the resonances.
between bands using this type of antenna which complicates the tuning of
the various dipoles. Be ready for a lot of ups and downs during tuning.
That's for sure.
There is no best antenna for anything. The standard to which the
relative efficiency virtually all antenna are compared to is the dipole.
What ever you do it isn't wrong,just different.
BTW: I believe the current cost for a B&W 160-6 non stainless steel
antenna is about $225US from most sources.
And, it would be quite straightforward to build one yourself, if you
have time and materials available. Look up B&W's patent at
http://www.uspto.gov/ for complete construction details. (I think the
patent number is on the B&W website) The patent is expired, by the way,
so you're not infringing to build one. Probably the only hard thing to
come by might be the big resistor, but that can be improvised in many,
many ways. (blocks of charcoal, pipes with salt water, etc.)