The devil is in the details... Note that I included the words, "decent
top hat"...
For 40 it should pull the vertical close to resonance...
For 80 I would not argue with your prescription for an outboard
loading coil to help the tuner efficiency...

BTW Ed, a coil Q of 1000 is going to be very tough to hit... If you
do get it please share the details...



Well, I may have stretched the Q factor a bit.... but in looking at
the following site, I would suppose its possible....

http://www.texasbugcatcher.com/cata/tbcspec.htm#6inch

scroll down until you view the #680 coil and read his text below.
That is what I had in mind if building a center loaded vertical. I
would not use a top hat in my case.

Per other comments in this thread, I see that perhaps I may get best
performance by using a combination of center loaded for 4MHz and using a
tuner for 40... and maybe 60. I'm really not interested in any other
bands.

As for radials, remember, even though intended for fixed station
use only, this is still a mobile antenna, and my RV parking situation
in many crowded spaces will preclude the layout of radials of any
significance.


Thanks for all the "food for thought" on this.


Ed K7AAT

Ed, K7AAT wrote:
"I`m really not interested in other bands."

Phil Rand, W1DBM, wrote a QST article on "Antenns for Travel Trailers
and Campers" which was reprinted in the 1978 "Antenna Anthology".

Phil shared his experience and measurements on 3963 kHz using various
antennas on the Airstream Travel Trailer Net.

Phil found that the best temporary antenna was a high dipole. Next best
was a loop antenna in which the Airstream trailer was included in the
lower art of the loop.

Table 3 in the article gives 7 trailer antenna choices and their signal
strengths as compared with a home station dipole at 50 ft. high.

Best regards, Richard Harrison, KB5WZI

Phil Rand, W1DBM, wrote a QST article on "Antenns for Travel Trailers
and Campers" which was reprinted in the 1978 "Antenna Anthology".

Phil shared his experience and measurements on 3963 kHz using various
antennas on the Airstream Travel Trailer Net.

Phil found that the best temporary antenna was a high dipole. Next best
was a loop antenna in which the Airstream trailer was included in the
lower art of the loop.

Table 3 in the article gives 7 trailer antenna choices and their signal
strengths as compared with a home station dipole at 50 ft. high.

Best regards, Richard Harrison, KB5WZI




I do have a homemade short Inverted V for 75M, ( 24' per leg )
which I pack around.... but as I have stated, most of my parking
situations preclude putting out anything beyond a very short perimeter
around my rig.... necessitating a vertical, ( with very short radials at
best). I will try to find that publication, but unless it includes
verticals for 75M / 40M, it probably won't help much in my case. Thanks
anyway!


Ed K7AAT ( 30' Class C motorhome, BTW )

Ed, K7AAT wrote:
"....but as I stated, most of my parking situations preclude putting out
anything beyond a short perimeter around my rig.... necessitating a
vertical, (with very short radials at best)."

Phil faced the same challenge. Item (1) of his summary says:
"Carry a complete set of mobile whips for lunch stops, or other
occasions where you do not have the time or room for anything better."

First on the list in Table 3 is:
"Hustler 75-meter mobile whip mounted vertically on the rear corner of
trailer...... S7"

Item (2) says:
"If at all possible, use a 1/4-wave counterpoise clipped tothe trailer
when using a mobile whip."

Second on the list in Table 3 is;
"Same as above, with 60-foot counterpoise wire connected to
trailer...................................S9"

So the counter poise adds about 12 dB to the signal.

A 15-ft high (at the center) 120-ft long dipole is S9+20 dB in Table 3,
but surprisingly the loop including the trailer is its equal. The loop
is only 30 feet long, or almost the length of the trailer.

Best regards, Richard Harrison, KB5WZi

Phil faced the same challenge. Item (1) of his summary says:
"Carry a complete set of mobile whips for lunch stops, or other
occasions where you do not have the time or room for anything better."

First on the list in Table 3 is:
"Hustler 75-meter mobile whip mounted vertically on the rear corner of
trailer...... S7"

That's all I have right now. 75M resonator, and the antenna is
mounted on top my rear ladder.... which is well bonded to the chassis
frame down below. It works rather well, I believe, but both I and my
wife don't want me climbing the ladder for installation/removal, or
tuning purposes.




Item (2) says:
"If at all possible, use a 1/4-wave counterpoise clipped tothe trailer
when using a mobile whip."


Will try that...


Second on the list in Table 3 is;
"Same as above, with 60-foot counterpoise wire connected to
trailer...................................S9"


I suppose a 60' coil of small wire wouldn't be hard to pack.... will
try that too, when space allows. BUT, since I'm mostly on 75/80,
whats the difference between the first two, anyway?


So the counter poise adds about 12 dB to the signal.

A 15-ft high (at the center) 120-ft long dipole is S9+20 dB in Table 3,
but surprisingly the loop including the trailer is its equal. The loop
is only 30 feet long, or almost the length of the trailer.


Well, certainly don't have space for that dipole, and the RV is
fibreglass so no easy way to include it in a loop.


Also, though I didn't previously mention, don't want the antenna to
be that noticable. A vertical has less visual impact, in my opinion, in
that area.

Thanks, Richard.


Ed K7AAT