Thanks much for your thoughtful and informative reply, Jim. My comments
are interspersed.
On 1/26/2014 10:32 PM, Jim Brown wrote:
Some other thoughts. It is critically important that the shield of all
cables be connected to the shielding enclosure at both ends, and ONLY
to the shielding enclosu
On 1/26/2014 7:18 PM, Randy Farmer wrote:
Unfortunately, in my case the shack IS part of the antenna field and
there's nothing I can do about it short of removing the antenna.
Yes, when the antennas are in close proximity, they radiate RF into the
shack, independent of common mode on the feedl
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I'm stuck on a very small lot with a pretty ugly RF environment. My
station is on the second floor of the house and the SteppIR is mounted
on a 10' roof tower directly over the station location. The feedlines
and control cables go down the roof and then enter under the eaves from
near ground le
Randy,
You might have better success with applying the 2.4 inch mix 31 toroids
to your feedline rather than trying to eliminate RF intrusion on every
cable in the shack.
In other words, kill the common mode current at its source and you may
not have to add additional ferrites on all your sha
Thanks to all the folks who replied with advice, both on and off the
list. I spent the better part of the weekend working the problem and
thought I'd update y'all on what I found.
It turns out there were two major problem areas. The first was RF
getting into the K3 via the ACC jack from the co
On 1/22/2014 7:36 PM, Randy Farmer wrote:
I've put a bunch of ferrites on the cable and this has reduced the
current on the cable but not eliminated the RFI problem.
"A bunch of ferrites on a cable" won't do much at HF. You must wind
multiple turns through the core to make a dent in RFI at 14
Howdy, all. I'm attempting to cure a weird RFI problem that is affecting
a K3/KPA500 combination. I've done some work to troubleshoot the
problem, but before I get too much deeper into detective mode, I'm
looking to see if anyone else may have experienced this problem and
maybe even cured it.
Part of the difficulty is an assumption that 1) there really is an antenna
that will work on all bands, 2) that balanced feedlines do not have common
mode current, and 3) that just about any feedline and transformer
combination will work. There is an awful lot of "all-band" stuff that is
really sn
On 1/9/2013 10:59 AM, David Gilbert wrote:
More importantly, a balun with a ruined core is going to look bad for SWR
Please delete the word "balun" from this discussion, and use the words
"unknown black box" instead. That's because the word "balun" is used to
describe at least a half dozen c
quot;
To: "'David Gilbert'" ;
Sent: Thursday, January 10, 2013 1:19 AM
Subject: Re: [Elecraft] KPA500 RFI problem
I agree that the balun should be checked but that it is likely NOT the
issue
here as it works on the other bands. If it is replaced, using a 1:1
common
mode chok
I agree that the balun should be checked but that it is likely NOT the issue
here as it works on the other bands. If it is replaced, using a 1:1 common
mode choke (not just a voltage balun or series of ferrite cores on the coax)
would be a good thing to try. I opted for the 10KW rated version as
From a troubleshooting point of view jumping right to the balun
requires making a lot of assumptions, most of them unwarranted given
what little we know so far from his post. More importantly, a balun
with a ruined core is going to look bad for SWR no matter what power
level is fed to it, a
Dave,
Most likely a tuner is being used.
If the balun failed one might not notice that since one generally tunes
to min SWR. Unless one recognizes something changed, one wouldn't know
it failed. This is especially true for auto tuners.
This "not knowing it failed" is wide spread for bead ba
If that balun had overheated and become ruined on 12m it almost
certainly would have affected other bands as well. A ruined balun is a
changed balun.
Dave AB7E
On 1/9/2013 7:26 AM, Brian Alsop wrote:
Sounds like the 4:1 balun may be overheating on 12M. Chances are if
you've been doing
Sounds like the 4:1 balun may be overheating on 12M. Chances are if
you've been doing this for a bit, it's ruined. Heat anneals the core
and changes it's electrical properties for the worse. Heat may have
cracked it.
Now whether a 4:1 balun is the thing to use is another issue.
You don't sa
I strongly suspect you have a common mode problem. These can be very
frequency dependent.
Read: http://audiosystemsgroup.com/RFI-Ham.pdf especially the section on
common mode chokes. There is a cookbook near the end for band specific
chokes.
For more details on the math read:
http://fermi.la.asu.
True. That is a possibility, of course ... that on 12m the voltage
maximum just happens to hit a weak spot in his feed system. In that
situation, adding some feedline could shift the maxima to a location
better able to handle the high voltages. I think I'd still want to find
that weak sp
On 1/8/2013 6:58 PM, Ron Kenwood wrote:
Fred:
Should have done that first, but I got tunnel vision on the RFI
solution. I have an AIM4170B which should do the job. I will let you
know how it goes.
OK, don't jump to conclusions though. If the impedance you measure on
the coax side of the balu
I was stating what worked for me on 80m. It shifted the voltage peak to
another portion of the feed, though the SWR was the same.
It brought the apparent SWR without the KAT500 from 24:1 down to a range
that was more acceptable to the tuner.
With the collection of 'stuff' that most of us collect
He said that his SWR on 12m was already low, so I don't see how that
helps a lot.
Dave AB7E
On 1/8/2013 6:40 PM, Rick Bates wrote:
Try altering your feedline length (which means resetting the KAT500 memories
too). I had a similar issue on 80M.
However in my case, it made no difference w
That doesn't sound like RFI. My guess would be that something is
arc'ing over between your amp and the antenna. That could be happening
at any one of several places (particularly at connections or inside the
balun). If it's close to the shack you could probably hear it ... if
it's in the f
Try altering your feedline length (which means resetting the KAT500 memories
too). I had a similar issue on 80M.
However in my case, it made no difference when I added 30' more window line
but changing the coax length (+~30') allowed it to load. The doublet length
is 170' per side (all HOA steal
It really sounds like something is breaking down when you transmit on
12m, not sure where RFI fits into this. The impedance at the balun-end
of your ladder line can be just about anything depending on frequency
[and length of the line]. The 4:1 balun will divide the magnitude of
that impedanc
At least I'm pretty sure its an RFI problem. I have a K3, KAT500 and the KPA500
connected as recommended with Elecraft DB15HD cables. The antenna is a 120ft.
doublet fed with ladder line to a 4:1 balun and 10ft of coax to the KAT500. I
have a comment point ground to a ground rod six foot from th
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