In message , Roy Lewallen
writes
Trevor Day wrote:

Excuse me for 'jumping in' here, it was difficult trying to locate a
bit of the thread that referred to the current title (CFA) I would
like to ask you learned chaps a question about the 'EH' antenna which
I appreciate is not the same as the CFA but its near enough for me:-)
I have built a couple of these and used them on 40m. Performance
hasn't been brilliant but they have worked and I was reasonably
satisfied with the contacts achieved considering the fact I used a
barefoot K2 at around 10 watts o/p and the antenna was sat on the
shack bench connected to the K2 by a 1 metre BNC to BNC cable laid
across the bench. (I only mention this last to try and forestall the
inevitable comment that the feeder does all the work)
All of this was done out of interest just to see if the antenna
worked at all, as my gut reaction was, and still is, sceptical
regarding the claims of its method of operation. I am not a
mathematician, so the various lengthy discussions regarding Maxwell's
equations et al pass me by; I am more interested in the practical
aspects of this rather than the theory. My question refers to the
SWR bandwidth achieved using this system. For an electrically very
short antenna of this type I expected something extremely sharp at
resonance, perhaps in the order of 5 or 10 KHz between the 2:1 SWR
points. In practice, the 2:1 SWR points are some 100 KHz or so
apart. When fed with 100 watts from an IC706, the antenna itself
does not get warm and neither does the short feeder so it doesn't
appear to be acting as a dummy load. Can someone satisfy my
curiosity and tell me (drawing comparisons with springs and dampers if
need be:-) how this is achieved.
Thanks,
Trev G3ZYY


Sigh.

A couple of questions:

1. Have you tried using something like a loop or other non-magical
antenna of similar physical size for comparison? Or putting a 20 dB pad
between your rig and a decent antenna? Most people are amazed at how
much they can do with 100 mW.
2. I assume you're using a "phasing network" or some similar device to
achieve whatever it is the antenna is supposed to accomplish. The wide
bandwidth is a sure sign of loss, and the majority of it is just about
surely in the "phasing network" and/or whatever matching network you're
using. Have you checked to see if either of them is getting warm after
a few minutes of key-down (with breaks to ID of course)?

But don't be surprised it they don't. If you're running 100 watts of
CW, your average power output is probably no more than 20 watts while
transmitting. If you're running SSB, it's considerably less than that
unless you're using serious compression. Try running your rig normally
(keying or talking) to a good-sized dummy load and see how long it
takes for it to get noticeably warm. Then imagine it to be the size of
your matching/"phasing" network and think about what you'd expect to
happen if it were absorbing *all* your transmitter's power. It is,
after all, absorbing most of it.

Roy Lewallen, W7EL

Roy,

I think you got as far as my first paragraph and didn't read any
further.

I am not attempting to justify this antenna or the way it works, just
trying to get an explanation for one aspect of it. If you had read what
I had written you would have seen the answer to your questions above.

Is it possible to 'mismatch', for want of a better expression, a loop to
achieve an equivalent bandwidth? I have constructed many short
verticals for portable and mobile use over the years, but have always
experienced narrow bandwidth. It is this aspect of the 'EH' that I
would like to understand.

btw, starting your answer with "Sigh" might be justified if I appeared
to be ignoring your continued advice but surely not at first meeting?

Trev G3ZYY
--
Trevor Day
UKSMG #217
www.uksmg.org