The reality of mobile ops is they antennas used will be inefficient for bands below 20mhz.
Reason is loading coils are a required thing to tune out the reactance of a short antenna.
There is no way around that.?
FOr 20M antenna efficiency is about about 8ft tall will be reasonable about 33% as its pretty
close to 1/2 size.? Center fed is about the best.
For 40M its about 1/4 size and allowing for the fact that cars are a terrible counterpoise for
the antenna so efficiency under 10% are the norm.? IF you can tolerate a taller than 8ft
antenna that helps, center loaded is best.? Do not use an antenna tuner as you at the wrong
end of the cable.? Its best if the tuner is at the base of the antenna.
K0BG has a very complete site on how to get the best out of a mobile antenna.
I run 40M mobile QRP using KNQ7A or FT817 and the antenna is a cheap 40M 8ft
centerfed whip?with mods.? The mods are a 9 turn 1-inch dia coil from the base to
ground to load the antenna.? Then the antenna itself has the longest whip section
possible at the top and is tuned by removing some of the plastic shrink and removing
turns to keep it as long as possible.? This is more efficient than shortening the whip
to tune it.? Its good for about 30khz either side of where tuned.? ? Using a tuner to
get more bandwidth results?in?a significant loss in efficiency as they antenna is then
untuned. I verified this with a field strength meter.? However those antennas are
cheap (about 20$) and I can carry two (one for 7163, and 7250) in the bed of the pickup.??
Ignition noise it a problem with the car/truck... fix it and then you hear the other near you.
Allison
