## Mine worked fine, bought last year. I calibrated it with 50 watts into a
dummy load.
50 watts = 1 Amp into 50 ohms. But the current loop/probe has to be looped
around either
the center conductor.....or the braid, but not both. Same as clamping on a 60
hz circuit,
only one conductor passes through the probe. Otherwise the opposing fields
will cancel.
## Dunno if it will work on 6M or not. My xcvr does not have 6M capability.
## I dont see any other device available commercially. The MFJ-854 will fit
over
a .405 cable, like RG-213. It will NOT fit over RG-214..which is .425 cable.
And it wont fit
over LMR-600, LMR 1200db, .5 inch heliax etc. In those cases, a short
jumper of 213 U, or
RG-393 can be used, like where a lightning arrestor can be temp removed..and
replaced with a
213 jumper. Or a 213 jumper installed at the remote switch box, or a bulkhead
etc.
## Besides CM choke effectiveness, it can also be used on radials, and items
around the home.
You would be surprised where RF current ends up, in places you would not have
thought, like
clothes lines, AC wiring, alarm wiring, stereo gear, etc. That list is
endless.
Jim VE7RF
From: Dave Sublette
Sent: Wednesday, July 1, 2020 10:55 AM
To: Jim Thomson
Cc: kj6y--- via TowerTalk
Subject: Re: [TowerTalk] Common Mode RF choke on a 50 MHz yagi
Checking the eHam reviews shows LOTS of issues in Quality on the unit. Unless
recent product has been improved, I am hesitant to order one.
K4TO
On Wed, Jul 1, 2020 at 1:50 PM Dave Sublette <k4to.dave@gmail.com> wrote:
The MFJ854 is rated from 1-30 MHz. Will it work on 5 MHz? How high can we
"fudge"?
Dave, K4TO
On Wed, Jul 1, 2020 at 1:28 PM Jim Thomson <jim.thom@telus.net> wrote:
Date: Sun, 28 Jun 2020 15:10:18 -0700
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
To: k4to@arrl.net, jim@audiosystemsgroup.com
Cc: kj6y--- via TowerTalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] Common Mode RF choke on a 50 MHz yagi
<The simplest way to make a 50 MHz common mode
<choke is to use 56 inches of coax and connect
<one end to the feedpoint and connect the shield
<of the other end to the boom. Then connect
<your regular feedline to the end of the
<56 inch cable. Let the coax hang down in a
<lazy "U" away from the boom. Whatever you do,
<don't be "neat" and tape it to the boom.
<I suspect this configuration is somewhere
<in the ARRL VHF handbook.
<73
<Rick N6RK
## This is common mode, not differential mode.
So its a physical one quarter wave, not an electrical
quarter wave.
## 246 / 50.125 mhz = 4.9077 feet long.
=58.892 inches long.
## With coax taped to boom, there is now capacitance
between braid of coax..and boom. This is easily measured with
any digital LCR meter. The CM balun now has to be 2-3% shorter.
= 57.125 inches..... to 57.71 inches long. It might even have to be
shorter. Using Ricks 56 inches, thats a 5% shortening. No loop
required,
except for normal rotor loop.
## Then the Z is sky high at the feed point of the insulated DE. No
requirement for a series string of torrid CM chokes.
## To test, use a clamp on RF ammeter, like a MFJ-854 or similar.
The 854 will read CM current down to as low as 1 ma...or less.
The 854 is superb to see if a CM choke is really working, or if you want
to compare different CM chokes. Just make sure you measure at the same
place
in the coax..downstream. Mark the coax with some painters green tape etc.
You
can also measure CM current in several places if you want. Take the
readings in
several marked places, swap CM chokes, then they will either rise, stay
the same, or fall.
Jim VE7RF
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