[Mobile-Portable] Mobile antenna tuner questions

[Jim Miller]

It sounds like JV has done a lot to maximize the efficiency of his
installation as far as grounding all parts together and using the longest
stinger that is even marginally practical.  I use the Hi-Q screwdriver and
use a 11 meter whip as the stinger making the antenna 13 ft 2 inches in
overall height.  I too know where all the low trees are.

I am very satisfied with it's operation BUT as is being stated here, the
radiation resistance spells it all out.  And for the lower bands, mobiles
have a HARD time getting much of anything out.  I had purchased a mobile amp
but am so satisfied with the operation  of the screwdriver, I now have no
intention of installing it.  It is very satisfying because it IS a mobile
and is handicapped because of it.  Radiation resistance has a lot to do with
the LENGTH of the antenna in wavelengths and a 9 or 10 or 12 ft antenna on
80 or 160 is terrible, even on 40 or 20 it isn't the best.  Radiation
efficiencies are LOW.  Doing all you can to make everything else work as
good as possible makes a big difference but you aren't going to compete with
a base setup, period.  Think about it, do you think any mobile is better
than a base (unless the base has a serious PROBLEM)?  Not hardly.

Have fun with the mobile and enjoy it.
73, de Jim KG0KP

----- Original Message ----- 
From: "MELVYN EVANS" <gzerogqk at btinternet.com>
To: "Mobile-Portable Reflector" <mobile-portable at mailman.qth.net>
Sent: Thursday, February 09, 2006 3:54 PM
Subject: Re: [Mobile-Portable] Mobile antenna tuner questions



--- Dick Flanagan <dick at twohams.com> wrote:

> At 11:23 AM 2/9/2006, JV wrote:
>  >
>  >    Sorry, I am going to disagree with you on your
> statement that a 20 M
>  >mobile antenna
>  >only radiates 30 watts. I county hunt with a
> modified Hustler and at the
>  >base of the antenna I have
>  >100 watts from my IC-706MKIIG. The antenna is
> mounted on the roof in the
>  >center of my Cherokee.
>
> I think the question relates to how many of those
> 100 watts actually
> radiate as RF as opposed to heat.  This "radiation
> efficiency" is
> depressingly low in mobile installations where poor
> grounds, inductive
> loading and electrically short (as a function of
> operating wavelength)
> antenna elements are the norm.
>
> If JV's antenna system is able to realize a 30%
> radiation efficiency on 20
> meters, I applaud and envy him.  Once you get
> further down to the lower
> frequencies (80, 160 M) radiation efficiencies in
> the single-digits quickly
> become the norm.
>
> 73, Dick
> --
> Dick Flanagan K7VC NV SM
> E-mail: k7vc at arrl.org
>
> ----
> Your Moderator: Dick Flanagan K7VC,
> mobile-portable-owner at mailman.qth.net
>
Hello Dick,

Can I quote you information on mobile antenna's from
an old Radio Society of Great Britain Handbook which
as you know is a knowlegeable sort of organisation
when it comes to discussing amateur radio

160 m. 32 watts output/ Efficiency 0.25%/ radiated
power 80 mw

80 m. 100 watts output/ Efficiency 1.0% / radiated
power 1 watt

40 m  100 watts output/ Efficiency 7%   / radiated
power 7 watts

20 m  100 watts output/ Efficiency 10%  / radiated
power 10 watts

Sorry Dick, my memory was more optimistic than the
fact ! The figures are even worse than I remembered. I
hope I haven't spoiled your day.

Kind Regards,  73,  Mel
----
Your Moderator: Dick Flanagan K7VC, mobile-portable-owner at mailman.qth.net