Hi Russ,
I love OCF antennas, (I have one in the air here and one I just finished
building a balun for another) but one thing they are NOT is symmetrical.
Because of that and the fact that they are usually fed with 4:1
voltage-mode baluns, the outside of your feedline is probably crawling
with those pesky common-mode currents. (both TX and RX, but TX is your
problem of the moment) Grounding the shield of the coax would only be
effective on a single frequency, and then only if you knew where the
nodes were on the feedline.
The thing that actually works for me is stacking lots of Mix 31
Fair-Rite ferrite beads on the coax. In my case I have two stacks of 10
Fair-Rite 2631102002 1/2" ID Mix 31 beads, one on each end of the coax.
(If anyone wonders why I bother with the stack at the antenna I'll
explain separately) Note these are NOT "snap-on". Snap-on beads are more
convenient, but I don't care for them. If that's the way you want to go,
though, the Fair-Rite part # is 0431164181 .
** NOTE: If you're going to use an amplifier, don't go with a small
number of beads. If the choking impedance is fairly low the beads will
heat up. You can get the per-bead impedance at a given frequency from
the Fair-Rite data sheets.
One of the best and most reliable places to buy beads from is Mouser
Electronics. You can find them by the Fair-Rite number using the
Fair-Rite number, or:
Solid bead: 623-2631102002
Snap-on: 623-0431164181
My .02, at least...
73,
Jim, N7CXI
On 10/30/2010 12:00 PM, Russell Magnuson wrote:
Hello all,
I have been fighting a problem with my Flex-3000 setup (or one that it is a
victim of) which I believe... is related to RF getting back into it and
freezing it up (Problem: display wave form freezes on transmit after
modulation, Flex-3000 requires a power cycle/PSDR needs to be restarted on
my notebook PC).
At first I thought it was a problem with my firewire card and all that, but
eventually got to try transmitting into a dummy load and under this scenario
the rig does not freeze up when transmitting (all the way up to full power
out/100w).
Other details:
* 50¹ of LMR-400 feeding a Radiowavz OCF DX 80 ( replaced RG-8X with the
LMR-400 as part of my debug process here)
* Insertion/use of an external tuner does not seem to change the symptoms or
prevent freeze up
* Increasing output power (and Mic gain to drive it) beyond a few watts into
the antenna causes it to crash
* Problem seems to be worst on 40m, but I have had it crash on 20m as well.
Higher bands seen less prone to crashing
Grounding:
I have been trying different grounding things but to no avail. I DO NOT
currently have a 8¹ rod handily pounded into the ground nearby. I have tried
the incoming copper water pipe in addition to normal A/C house ground (I
also tried a 50¹ run of RG-8x to that incoming water pipe, with the C/S
shorted on the pipe end and a .01uf ceramic cap between the center and the
shield on the other end, where I then connected the center to the GND on the
Flex-3000).
Other rigs:
Prior to purchasing the Flex-3000 I have been running my FT-897D into this
same antenna setup with no known (or detected) issues related to ground or
RFI, etc.
Thoughts? Ideas? Theories? What am I missing here? Is there anything in the
Flex-3000 that maybe is futz in some way that would make it hypersensitive
to some RF(???) in the shack? Or am I missing some other angle here?
Thanks in advance,
Russ, KF1K
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