In a message dated 26.11.99 20:03:11 Pacific Standard Time, K7GCO writes:
<< In a message dated 26.11.99 11:59:08 Pacific Standard Time,
alsopb@gloryroad.net writes:
<< Something has really been bothering me. It is the statement which often
appears here. "Balanced line doesn't radiate" I wonder. I think this
statement is only true if it is feeding a matched balanced load and the RF
source is matched and balanced. In practice, is this true enough to still
state "balanced line doesn't radiate"? Anybody who has gotten RF into the
shack must conclude that balanced line does indeed radiate. I'd like to
suggest that the press release is generally false.
"NOPE!"
How much it radiates (in practice) is the question. Who would like to offer
some quantitative data to determine how much load/or source imbalance is
necessary to get significant feedline radiation? It would be useful to know
if any of our non-straight wire antennas over non-flat (varying height of
antenna above ground), obstacle studded terrain present sufficiently balanced
loads or not--especially those for the lower frequency bands.
Only those offering quantitative data are invited to reply. I'm not
interested in innuendoes and testimonials.
de Brian/K3KO
"TRY EXAMINING AND USING THEIR TECHNIQUES."
>>
I keep suggesting the use of RF ammeters or any current measuring device
like 2 shunted light bulbs to check for balanced currents in open wire line
and 10:1 SWR doesn't cause feedline radiation. One ham thought that was too
much work.
I have an open wire line 1/4 WL long on 160M connected to a 75M
horizontal quad loop 20' off the ground which has a balanced 12,000 ohm
feedpoint on 160M and the Z at the end of this feedline is 17 ohms--that's a
26:1 SWR. It's matched with an unbalanced step down mobile toroid-in one leg
only--set on 17 ohms. Note!: Since this is 17 ohms in this one leg only
perhaps it was really a 34 ohm balanced Z at the end of the balanced line. I
only had to match 1 wire to get total transfer of power. The bandwidth is
narrow due to the severe Z step down ratio. But with a BC 3 gang variable in
the other leg I can tune it over the whole 160M band which is a very rare
feat--one tuning component and the ultimate of simplicity K7GCO style. I get
great signal reports on 160&80-75 and no TVI.
The transfer of RF energy from the rig to the antenna has certain ground
rules depending on how it's done. Learn them or stick to coax and SWR
curves.
Is the tuner shielded? When I learned how to do it right I no longer had
to shield the tuner.
Is the coax shield connected to the tuner chassis because the link is
grounded there? Is there a variable Xc in the ground side of the link? A
ground connection to a chassis is only a relative thing. It may not be the
open wire line spilling RF all over--the tuner could be.
I used balanced coax to a 2 element quad on 6 M as I had TVI with every
other 6M antenna and feed system I had using 100W. I used a Johnson MB with
a 6M tank coil and used a 200 ohm balanced link and a 1/2 WL coax (shield not
grounded on the tuner chassis) connected to give a balanced 200 ohm line from
50 ohm coax to the tuner. Despite an open tuner 15' from a TV on cable there
was no TVI.
15' from the TV is an open wire line used on 160-10M with 600W.
Whenever I did it right I've never had RF in the shack with either a
Hi-Z or a Lo-Z at the end of the open wire line. You need a serious review
of your RF technical and physical practices using open wire line--they leak
RF.
There was a tuner in QST a year or two ago using an unbalanced e
component L network to match balanced lines. Normally there would be RF
spill over on the tuner case and coax shield to the rig. About 20' of 50 ohm
feed line to the rig is coiled to form a RF choke to prevent the RF spill
over. This is a great tuner circuit.
I have even used a 1/2 WL of open wire line from a 1/2 WL 80M dipole
where I connected one open wire lead to the coax switch center lead and the
other balanced wire to the coax switch ground. Some call that a no-no--it
works! I then connected a BC variable in series with the grounded (rotor
grounded) wire to tune it up the band and even unbalancing the currents. No
RF interference anywhere from the connection process on the coax switch and
the HI-I or Lo-Z open wire line area and connection was right in the shack.
Open wire line requires proper handling or don't use it. That's all
that was used prior to say 1940 and for a some time after--I never stopped as
I haven't found any system any better. Some of QST's circuits in the old
handbooks etc didn't work as they never tried them. How many hundred dollars
of coax have been thrown away by the average ham and even me? I haven't
thrown one open wire line away since 1936 except that cheap 450 ohm stuff.
Long live open wire line and properly designed tuners--build your own.
k7gco >>
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