For anyone interested, here is the link
http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm
MIght even put a photo up if it works. I am trying to adapt a large clamp
for holding glued joints to use as a spring mechanism to open and close the
Ferrite.
Dave
On Thu, Jul 2, 2020 at 11:28 AM Dave Sublette <k4to.dave@gmail.com> wrote:
> I have since started building one based on plans in RSGB by G0SNO. Looks
> like it will be a fun project.
>
> 73,
>
> Dave, K4TO
>
> On Thu, Jul 2, 2020 at 11:07 AM Jim Thomson <jim.thom@telus.net> wrote:
>
>> ## 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
>>>>
>>>> _______________________________________________
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> TowerTalk mailing list
>>>> TowerTalk@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>>
>>>
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