In message , Cecil Moore
writes
Ian Jackson wrote:
The question is, what are the consequences of having such a high SWR?
It all depends on how much attenuation the coax has. If the coax was
lossless, there would be no signal loss, regardless of the SWR.

True, but the value of Z0 of the transmission line has a
large effect. Let's say we are feeding one of those 5000
ohm antennas. The SWR on 50 ohm coax would be 100:1. The
SWR on 450 ohm ladder-line would be 11:1. Even if the coax
had the same matched-line loss as the ladder-line, it would
still be much lossier than the ladder-line - and much more
expensive.

I think that the secret is to make sure that antenna is not exact
multiples of a halfwave. This prevents the SWR being absolutely sky-high
- say, 'only' 20:1, worst case. The proviso is certainly that the coax
should be as lossless as possible. I'm happy to lose 3 or 4dB in the
interests of simplicity and good EMC. It's mainly 160/80/40 which I'm
interested in. There's just a load of foreigners on the higher bands!

Some time ago, I did some (more) Smith Chart guestimation with the
object of trying to find which 'magic' inverted-L antenna lengths would
present 'reasonable' impedances on all (or most) of the amateur bands up
to 30Mhz. [Many years ago, I reckoned that around 185 feet was a good
length.] However, my recent efforts ended in dismal failure. In the
meantime, I will continue in complete ignorance, and use my antenna as
it is, accidentally having the occasional QSO and causing no obvious
interference problems. But, after all these years, I might treat myself
to an automatic tuner for the far end of the coax.
--
Ian