12 meter K3 RFI from nearby FM station

[James Bennett]

And if a second receiver is not available, perhaps hook the K3 up to a battery and transport it to another location, as far away as possible from your QTH.

Jim Bennett / W6JHB
Folsom, CA

> On Feb 11, 2016, at 11:44 AM, Bob McGraw K4TAX <[hidden email]> wrote:
>
> One other item, if available, try another brand/model radio using the same power supply, location, antenna and such.   If it is present on that radio, most likely it is radiated.  If it is not present, then most likely it is generated in the K3.  {To which that is an entirely different can of worms.}
>
> 73
> Bob, K4TAX
>
>
>
>> On 2/11/2016 12:55 PM, Jon Zaimes wrote:
>> Yes, that is the case. Hearing it on both of my K3 transceivers with only
>> the 12v power cable connected, nothing else (listening on speaker).
>>
>> Thanks to all for the tips. Still absorbing the advice before proceeding.
>>
>> 73/Jon AA1K
>> Felton, Delaware
>> www.aa1k.us
>>
>> -----Original Message-----
>> From: Elecraft [mailto:[hidden email]] On Behalf Of Alan
>> Sent: Thursday, February 11, 2016 12:04 PM
>> To: [hidden email]
>> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>>
>>> On 02/10/2016 03:57 PM, Jim Brown wrote:
>>> Yes, this hit me between the eyes as well. The K3 has Pin One Problems
>>> at many (most?) connectors, so RF current flowing on shields of cables
>>> plugged into those connectors will couple into the K3. I've been
>>> preaching to Wayne about Pin One Problems since 2004, when we met in
>>> Dayton.
>>>
>>> If the problem is around 90 MHz, I'd use multiple one-turn and two
>>> turn chokes with #43 material on every cable except the SO239 output,
>>> which IS actually bonded to the chassis. Also choke the power cable.
>> But it sounds like he was still getting the problem with no cables connected
>> to the K3:
>>
>> On 02/10/2016 06:58 AM, Jon Zaimes wrote:
>> ...
>>  > Even when ALL cables are removed (only the power lead connected).
>>  > Grounding or ungrounding made no change. I tried the radios on a  >
>> battery but still had the RFI. Tried some ferrites on the power  > lead but
>> no change.
>>
>> I suppose it could be a "pin 1" problem on the power leads.  It's kind of
>> hard to avoid that with an Anderson PowerPole connector.  Probably
>> additional low-pass filtering on the DC input would help.
>>
>> Alan N1AL
>>
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[Jim Brown-10]

On Thu,2/11/2016 10:55 AM, Jon Zaimes wrote:
> Yes, that is the case. Hearing it on both of my K3 transceivers with only
> the 12v power cable connected, nothing else (listening on speaker).

I'm assuming this means nothing at all plugged into the back of the rig
-- no control, no audio, nothing to the BNCs, nothing to the Aux power
jack.

By all means choke the 12V DC cable. Since the RFI is VHF, this IS an
application for a "string of beads" choke. #43 clamp-ons would be the
weapon of choice, either single turn or two turns. #31 would also work.
What you want is a clamp-on with two turns through it, a short length of
the power cable, then another clamp-on with two turns, a short length of
cable, then another clamp-on with two turns, and so on. Select the size
of the clamp-on to fit the number of turns. Turns should be widely
spaced. Do NOT run two turns through a string of clamp-ons -- that will
take the resonance too low in frequency to work at 90 MHz.

You can see data for the choking Z of individual Fair-Rite parts with
one, two, and three turns on the data sheets for those parts. Click on
the part number in the table of parts to get that data sheet, then
scroll all the way down for the impedance plots. You may need to click
on that to get the three turn plots.

73, Jim K9YC


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[Phil Kane-2]

On 2/10/2016 1:08 PM, Walter Underwood wrote:

> A long time ago, I visited the transmitter room at the top of One
> Shell Plaza in Houston. There were nine 100 kW FM transmitters on the
> same antenna. The RF plumbing was something to behold, with big stubs
> like that all over the place.

That's in the same category as the ten FM transmitter diplexer at
Stonehenge Tower in Portland but not all of the stations are 100 KW ERP.
 In addition to those on the master antenna, there are several FM low
power/translator/auxiliary transmitters as well as a few ham repeaters
on different antennas on the same tower.

Stonehenge Tower itself is a self-supporting three-legged monster, with
the coax sewer pipes running up a center 4-foot diameter shaft.  The
site ground level is 303 m AMSL and the center of radiation of the
antenna is 170 m above that.  It is a work of art.

Our SBE chapter gets up there for a weekend potluck meeting every other
August (we go to a different nearby 1000-foot tower site in alternate
years).  We haven't tested how an Elecraft will operate in any of those
fields although one of our members lives in the house adjoining the base
of the tower, a former radio studio building.

73 de K2ASP - Phil Kane
Elecraft K2/100   s/n 5402

>From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
Vice Chair,  SBE Chapt. 124
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