No, it sounds like you joined the conversation late, Jim.
And BTW, I started this thread and have followed every email on the drifting
topic.
All that you wrote is well known to me Jim, and was not the point of the
discussion.
We are debating whether the JVM is the best matchbox ever built, capable of
matching any and everything (as some here have claimed) or if it has limited
matching range (as I have stated and ARRL labs have reported). THAT was
the debated point.
And I've seen pictures of your shack with multiple resonant antennas in
Chicago. Looked great to me but . . .
Mine and most other people's neighbors would hang us from our coax if our
yard looked like that.
Now days, most of us are forced to live with "less is more".
We need the simplest, most stealthy wire antenna that will give us as many
bands as possible.
FAN DIPOLES work great but don't meet that criteria.
The choices boil down to either a dipole or loop fed with openwire, or an
OCFD.
In this thread we were [recently] discussing the openwire fed antenna and a
matchbox to match it.
When someone suggested the 132 ft. dipole fed with openwire into a JVM was
the best way to go, I stated that there weren't enough JVM's to supply the
demand of this group, let alone the entire ham market. And asked the
question where else anyone might buy one.
Then the claim was made that the JVM is the best matchbox ever made. Well
it's NOT. It is greatly inferior to the Annecke (see my explanation on my
web site) but can be modified to fix that (see my web site for instructions
how to do this).
Like all matchboxes, the JVM has advantages and disadvantages. It's
advantages, for one, is the isolation between input and output, helping keep
common mode current out of the shack, it does a good job of balancing the rf
current into each leg (see W8JI's report on this) and it has relatively high
efficiency (see W8JI's report on this). It's downside it its limited
matching range (See ARRL Labs report on this).
THOSE are my points. I back them up with good reference along with my tons
of experience using the JVM with all kinds of antennas for over 50 years.
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Jim Brown
Sent: Monday, July 18, 2016 9:46 AM
To: tentec@contesting.com
Subject: Re: [TenTec] OT: Question to the group
On Mon,7/18/2016 12:25 AM, rick@dj0ip.de wrote:
> Roger, then let's stay with resonant antennas.
> The feedpoint impedance is not only dependant on the impedance of the
antenna but also on the transformation of impedance due to the specific
length of feedline . . . which varies from one band to another.
Rick,
You miss the point. In general, multiband antennas are NOT resonant, and
they do NOT match the feedline within reasonable ratios. That's Gary's
point, and it's mine as well. There are lots of ways to make a single
antenna resonate on multiple bands. Fan dipoles, trap dipoles, even some
loaded dipole designs, and combinations of fans and loaded dipoles.
Barry at Hypower Antenna Co (it's a basement enterprise, I never remember
his call, but a good guy) sells a loaded dipole for 80 that is also resonant
on 40, and to which a 20M fan element can easily be added.
I've very successfully used a 160/80/40 version of that design at several
QTHs. See my website for construction details on fan dipoles, buy the coils
from Barry. Loaded antennas in general are not very broadband, so you'll
need a tuner. Also, in a fan dipole, the higher frequency element has about
half the SWR bandwidth of a non-fan dipole, but 40M is not a very wide band,
and neither is 20M (thinking percentage bandwidth, which is what matters).
I've VERY successfully used 20/15/10 fan dipoles, both in Chicago (only
30 ft high) and here in W6 (100 ft or so) before I had a SteppIR.
Also, consider this -- we're on the downside of the solar cycle, 10M is a
lot less open, 15M not a lot better. It was a down part of the cycle when I
moved to W6, and I lived 3 years in W6 before I made a Q on 10M beyond
single hop Sporadic E, and nearly that long on 15M. You guys in EU can work
another country single-hop Sporadic-E on 10M, but here in W6, we need the
F-layer to work anything but K, VE and XE. :)
73, Jim K9YC
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