"Antonio Vernucci" wrote in message
...
I wonder what you consider narrow bandwidth. 500 KHz seems to be about
par for a decent 6 m beam.


This antenna shows an SWR of 1.7 at 150 kHz below the resonant frequency,
where the SWR is just 1, so I consider it narrow. Another antenna I have,
also using an hairpin match but at 50 ohm instead of 200 ohm, is by far
broader. On both antennas I have about 100 feet of low-loss 1/4" Andrew
hardline, so the SWR is only slightly influenced by cable loss.

Talking with the manfacturer, he told me that he preferred rasing the
antenna impedance up to 200 ohm, instead than to 50 ohm, because a 4:1
cable balun can me more easily realized than a 1:1 balun. But doing so the
feed system Q factor increases quite a lot, causing a significant
bandwidth reduction. Moreover ohmic losses increase, due to the higher
circulating currents (for a given RF power), but I am not able to predict
whether such extra losses are significant or can be disregarded for all
practical purposes.

73

Tony I0JX
I don't think it is the balun. I measured a 4:1, 1/2 wave 6m balun made of
LMR240 and got a 2:1 SWR bandwidth from 40 to 60 MHz. This was with an
MFJ-269 and about a foot of 50 Ohm coax. Load was a 1/2 W 180 Ohm resistor
(measured high).

Tam/WB2TT

Tony I0JX
I don't think it is the balun. I measured a 4:1, 1/2 wave 6m balun made of
LMR240 and got a 2:1 SWR bandwidth from 40 to 60 MHz. This was with an MFJ-269
and about a foot of 50 Ohm coax. Load was a 1/2 W 180 Ohm resistor (measured
high).

You are right, it is not a balun problem. It is a problem due to the reasons I
had explained in my post, which had nothing to do with the balun.

73

Tony I0JX.