[ICOM] Re: Best antenna for 706 mobile?

[Bob Nelson]

I have been using the 706 with a High Sierra 1500
screwdriver antenna for some years, with outstanding
results.

Here's my opinion on using the AH-4 for mobile ops:

The main difference between using a tuner versus using
a good externally-loaded antenna is that the tuner,
due
to its small size is likely to have less electrical
efficiency.
You just cannot get away from the physical fact that
high unloaded Q is much easier to get with large coils
than with small ones.

The tradeoff is that the screwdriver antenna is a bit
unsightly for the XYL to put up with, as compared with
a sleek and skinny whip.

A couple of other things to think about.  The biggest
challenge in mobile ops (outside of 160m) is versatile
and effective operation on 75m.  If you don't care
much about that band, then this entire question
becomes much less critical.  Most people's operations
on 40m and higher can be easily satisfied with any
number of antennas.  The screwdriver is likely to be
more efficient than most, but the many brands of
helical and lumped-loaded short whips will work fine
too.  Its when you come down to 80m and 75m that
things begin to get really dicey.

If you go with the helicals or Hustlers on 75m you
will
need to retune the antenna frequently if you move
around the band much.  That is a real hassle in bad
weather.  With the screwdriver, you just hit a switch.

Finally, note that if you put a 75m antenna structure
together and it seems to have bandwidth of more than
about 15 KHz, you probably have a very lossy antenna.
You are getting the bandwidth at the expense of
losses - low loaded Q, due to low unloaded Q in the
structure itself.

In summary, if you want best versatility, I find it
very hard to beat a good screwdriver installation.
But if you prefer the sleek look and can put up with
a loss in TX signal strength, then the AH-4 may work
OK for you.  (I use an AH-4 at home with a 40-foot
wire, and it works fine, but for 75m not what a good
full-sized dipole would be.)

Finally, I disagree with the gent who said mobile
operation is a lot like QRP.  I find I can work just
about anyone I want with my 706 and screwdriver, so
long as I don't tackle the DX pileups.

73 - Bob K6KL