Thanks for all the answers. Intrigued by the lack of information
on Internet on the impedance of efhw-antennas (one value I found was
round 5kohm) I took the opportunity to become acquainted with the
EZNEC4-Demo and ran a few simulations of the efhwa as a straight wire
with the fed end near ground and an inverted V also. Considering
different geometries that could be realized by simple means I found a
large range of impedances between a few kohms up to 18kohm, probably
giving rise to high losses when matched to 50 Ohms - I have found
information on a "Z-Match using a toroidal Core Coil" by VK5BR that
shows efficiencies below 70% at 2kOhms for frequencies between 3.5
and 21 MHz, efficiency falling rapidly with increasing impedance.

On the other hand, a center fed inverted V has impedances between 36 and
52 Ohms, depending on the height (angle between wires) of the center. So
I am taking the advice of MK using this kind of antenna without any tuner.

Cheers
Andreas


wrote:
Or would be better to use a center fed inverted V with its low
impedance that can be mathed with smaller losses to 50 Ohms?

Pass go and collect $200.... Way better than any other
method...Scrap the tuner...Thats the last thing you want
for QRP...Center feed with coax...Can be lightweight rg-58...
You really don't even need a balun...In the unlikely event rf
at the rig is a problem, just roll a few turns of coax at the feed,
and tie wrap it...As a bonus, you can add wire, or insulators,
and use for other bands, or make it multiband, with insulators,
and jumpers to change bands...No tuner needed anywhere,
once it's set up. You could make one for all bands...
Would look kinda like this for a 20-40-80m version.....
-----------------o---------o-------00--------o----------o-----------------
You jumper all the insulators for 80..Only the inner ones for 40,
and none for 20...In that pix, you can't see the jumpers.....
Can be wires with gator clips, or whatever....I've used that
portable many times...Usually built on site from wire and stuff
I carry...But I usually just make them for 80/40....
MK