K2 has Hi Pwr with MD2 PTT

[Matt Osborn]

I was reading Jonathan Gottlieb's adventure wiring up an Heil Handi
Mic HM-IC and the 10 watts power out he saw when pressing the PTT.

I've been having some trouble checking in to the local 6m net
(complaints of distortion) when using my MD2 with my K2 and XV50.  I
had switched to using a Heil Proset and a foot switch which cured the
problem.  I did notice, however, that the power output with Heil
Proset was much lower than I saw with the MD2, so I increased the
compression to 3-1 and found that I was able to achieve full requested
power with the Proset.

After reading Jonathon's posts, I dug out the MD2 and did some further
investigations.  With the compression now at 3-1, I found that the MD2
would cause a steady 10 watt output as soon as I started to talk.

I have an indoor antenna (3rd floor apartment with severe
restrictions) so I know that I have RF in the shack.  I discovered,
though, that if I used the foot switch with the MD2 instead of the
built in switch, everything was FB.

Just for kicks, I left the foot switch plugged in to the mic cable and
used the PTT in the MD2.  Much to my surprise, it worked FB. As long
as I left the foot switch cable plugged in, the MD2 PTT works fine.
As soon as I unplug the foot switch cable, the MD2 PTT drives the K2
into full power as soon as I speak.

I'm pretty well convinced it's the RF in my shack that is the root
problem. However, I'm looking to see if there is something I can do
with the ALC circuit to overcome the difficulty.  Also, I thought
folks might like to know about this particular failure mode.
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[Matt Osborn]

Thanks, Don.  I came to the same conclusion myself, but I just had to
ask.  I've got the 4 1/2' counterpoise wire for 6m already in place,
but like all things, it's placement isn't optimum.

Having a tech license, I'm restricted to 2m, 6m & soon 70 cm, so the
counterpoise for those will be easily handled.

I don't seem to have the same RF problem with 2m as I can set up a 5
element logarithmic antenna that is much more directional.  The 6m
halfwave dipole is just spreads too much.

If I'm to stick with the program, I'll just have to move out in the
country and erect antennae outdoors to solve the RF problems.

Thanks again for the advice.



On Wed, 1 Mar 2006 08:50:23 -0500, "Don Wilhelm" <[hidden email]>
wrote:

>Matt,
>
>Making changes to the K2 circuits to 'workaround' an RF in the shack problem
>is an 'iffy' attempt to solve it at best, and may cause other unknown
>'strange happenings' along the way.
>
>Yes, you are describing a severe case of RF Feedback - many times it is not
>as obvious, it is good that you recognize it.
>
>The best cure that I know of for RF in the shack is a good RF Ground at the
>station common ground point.  If you have no other method of creating an RF
>Ground, connect 1/4 wave wires for each band of interest to the common
>ground point in the shack and fan out the far ends - the far ends should be
>isolated and insulated because they will have a high RF Voltage.  You can
>bend the wire as required to get around corners, etc, but it is best if run
>straight.
>
>For a quick check, try one for your most used band (only 4 1/2 feet for 50
>MHz) and see if it helps, and if so, add wires for the other bands of
>interest.
>
>The added length of wire going to your footswitch is probably acting like a
>part of one of these 'counterpoise' wires, but a measured length of wire
>will likely give more consistent results.
>
>73,
>Don W3FPR
>
>> -----Original Message-----
>>
>> I was reading Jonathan Gottlieb's adventure wiring up an Heil Handi
>> Mic HM-IC and the 10 watts power out he saw when pressing the PTT.
>>
>> I've been having some trouble checking in to the local 6m net
>> (complaints of distortion) when using my MD2 with my K2 and XV50.  I
>> had switched to using a Heil Proset and a foot switch which cured the
>> problem.  I did notice, however, that the power output with Heil
>> Proset was much lower than I saw with the MD2, so I increased the
>> compression to 3-1 and found that I was able to achieve full requested
>> power with the Proset.
>>
>> After reading Jonathon's posts, I dug out the MD2 and did some further
>> investigations.  With the compression now at 3-1, I found that the MD2
>> would cause a steady 10 watt output as soon as I started to talk.
>>
>> I have an indoor antenna (3rd floor apartment with severe
>> restrictions) so I know that I have RF in the shack.  I discovered,
>> though, that if I used the foot switch with the MD2 instead of the
>> built in switch, everything was FB.
>>
>> Just for kicks, I left the foot switch plugged in to the mic cable and
>> used the PTT in the MD2.  Much to my surprise, it worked FB. As long
>> as I left the foot switch cable plugged in, the MD2 PTT works fine.
>> As soon as I unplug the foot switch cable, the MD2 PTT drives the K2
>> into full power as soon as I speak.
>>
>> I'm pretty well convinced it's the RF in my shack that is the root
>> problem. However, I'm looking to see if there is something I can do
>> with the ALC circuit to overcome the difficulty.  Also, I thought
>> folks might like to know about this particular failure mode.
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>>  http://mailman.qth.net/mailman/listinfo/elecraft
>>
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>> Elecraft web page: http://www.elecraft.com
>>
>>
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>>
>>
>

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