On Tue,9/22/2015 2:05 PM, Rick - DJ0IP / NJ0IP wrote:
I agree that if you are going to run very high power, you should be running
antennas designed to better cope with that. The Windom is usually chosen by
people with limited space, living in congested areas. It is a compromise
antenna. Most of these people do not run such high power. I certainly
would not when using an OCFD.
Yes, it's a VERY compromised antenna, primarily because the common mode
problem makes it noisy on RX. AND a choke at the transmitter end is FAR
less effective than one at the feedpoint. The virtues of doing both are
reduced dissipation and the "egg insulator" to prevent the feedline from
being a parasitic element of a nearby vertical. Remember that when
Windoms and other OCF dipoles were first the rage, there were no
switching power supplies, computers, grow lights, plasma TVs, etc. to
produce RF noise. In those days, mostly we had power line noise and
leakage from the local oscillator of a TV, and the detected color
subcarrier.
Cost of Ferrite here in EU is indeed a problem. It's getting better.
The prices are coming down, especially if you buy in quantities.
I order my private ferrite together with Spiderbeam when they place larger
orders.
I continue to be baffled as to why EU hams don't arrange group purchases
to get quantity discounts, which can be quite substantial. The last
order for #31 2.4-in o.d. toroids I put together (a couple of years
ago) got us a cost, with tax and shipping around $4.
GM3SEK has suggested another method to save on ferrite cost. It uses the
principle that W2VJN described in the 2010 ARRL Handbook. I don't know if
there is a special name for this kind of choke.
I looked at the section on chokes in my copy of the 2010 Handbook and
found nothing credited to George. I saw Ian's chokes using those special
form oval #43 cores soon after he published them, and agree that they
are a fine design for the higher HF bands using what Farnell would sell
him. Indeed, that publication was what motivated me to explore the
parallel wire transmission line chokes.
Ian divides the hf spectrum up into 3 segments, low bands, mid-range bands,
and high bands. He uses multiple loops of coax through 2-cores (high bands)
or 3-cores (both other chokes) chunks of ferrite. These are large and ugly
but cheap; about $3 apiece.
FWIW, I published that multi-range recommendation in the first version
of RFI-Ham.pdf, I think around 2007.
73, Jim K9YC
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