http://elecraft.85.s1.nabble.com/KPA100-80m-poor-quality-SSB-tp372990p373000.html
39k and ** added a 1k resistor in parallel with RFC3 ***. There was no
reason given in the errata. Stewart put these changes into his KPA100 and
so have I. Our 80 meter performance is now normal. These two changes are
capacitance of D14. The 1k resistor spoils the Q of the resonant circuit
finally got tired of waiting. In my opinion the 1k resistor across RFC3 is
a very good solution. The change in R4 is not necessary if your bias
> So K2 Gentelmans...one question..
>
> To fix RF switching problem in KPA100 there are 3 way's available (posted)
>
> 1. 12pF to ground from 1n4007's junction (just mooves a problem arround)
>
> 2. 1K resistor instead of RFC3 (affects RX preformance and marginal
> switching at high power levels)
>
> 3. Change RFC3 100uH with 1mH choke (dont know abt side effects but shure
> want to know the current rating of choke, cause i suppose must be at least
> 150mA or more?)
>
> Which way is the best for now?
>
> All kind of Help is Wellcome!
> Thanks in advance!
>
> S55M-Adi
> K2-3204
>
>
>
> ----- Original Message -----
> From: "Stewart Baker" <
[hidden email]>
> To: "Don" <
[hidden email]>; "Elecraft Reflector"
> <
[hidden email]>
> Sent: Wednesday, December 29, 2004 7:29 PM
> Subject: Re: [Elecraft] KPA100 - 80m poor quality SSB
>
>
>>>> Although the 1k resistor mod seems to work there is a noticeable drop
>>>> in
>>>> received signals.
>>>> Modeling the KPA100 T/R switching showed this additional loss.
>>>> As a temporary measure until the official Elecraft modification comes
> out
>>>> I have replaced RFC3 (100uH) with a 1mH RFC.
>>>> My simulations show that the circuit resonance is now around 1.2MHz-
> maybe
>>>> lower. Tried all bands, can't find a problem.
>
>>>> 73
>>>> Stewart G3RXQ
>
> On Tue, 28 Dec 2004 18:11:15 GMT, Stewart Baker wrote:
>> On Tue, 28 Dec 2004 09:36:00 -0800, Don wrote:
>>
>>> Stewart,
>>>
>>> I have been in contact with Gary intermittantly since first coming
>>> across
>>> this problem in October. He assures me that Elecraft is working on a
>>> solution and will have something to say soon. Both the "12 pF" fix and
> the
>>> "1000 ohm resistor" fix have proved effective but are probably not the
> most
>>> elegant or foolproof ways of solving the problem. For instance, the
>>> 1000
>>> ohm resistor alters the reverse bias on D14 in a way that makes the T/R
>>> switch marginal at high power levels. I suspect that Elecraft is taking
>>> their time and checking out all of the possible effects of design
>>> changes
>>> and mods before committing to a final solution.
>>>
>>> We will just have to be patient.
>>>
>>> Don K7FJ
>>>
>>>
>>> The guests having departed - the Turkey finally disposed of - the booze
>>> consumed
>>> - thoughts turned to "Playing radio".
>>>
>>> I have been getting reports on 80m that my SSB signal had some "edge" to
> it.
>>> At first I put it down to RF feedback, but that was not the problem.
>>>
>>> I used my FT1000MP to listen to the 2nd harmonic of the 80m signal.
>>> Having read recent mails I first monitored the 3.5MHz signal and found
> the
>>> "Buzz" that others had reported.
>>>
>>> I then tried the following frequencies on 80 and noticed that as I
> increased
>>> the
>>> power control on the K2 the power output would suddenly jump, then when
> the
>>> control was turned ACW the power would reduce smoothly and then suddenly
>>> drop.
>>> It was also observable on the FT1000MP S-meter, accompanied by a click.
>>> It was like a form of hysteresis. All other bands gave smooth power
> control.
>>>
>>> The results were as follows:-
>>>
>>> 3.8MHz Low point=20W High point=70W Hysteresis=50W
>>> 3.7MHz Low point=25W High point=70W Hysteresis=45W
>>> 3.6MHz Low point=35W High point=70W Hysteresis=35W
>>> 3.5MHz Low point=40W High point=70W Hysteresis=30W
>>>
>>> Very unsatisfactory...
>>>
>>> I substituted a 1k resistor for RFC3, and all the 80m problems went
>>> away.
>>> Smooth power control on all bands and a better SSB signal on 80m.
>>>
>>> Many thanks to those who found/cured this problem that first showed
> itself
>>> on
>>> CW, I would certainly have spent a lot of time tracking this one down !
>>>
>>> I would suggest that owners of K2/100's check to see that their rig does
> not
>>> exhibit these symptoms as it can make quite a big difference to
> transmitted
>>> signal quality.
>>>
>>> I, like a previous correspondent think that Elecraft should make some
>>> comment on
>>> this design problem, and it's solution.
>>>
>>> 73
>>> Stewart G3RXQ
>>>
>> Thanks for the "Heads up" Don.
>> I will look forward to the official modification when it is released.
>>
>> 73
>> Stewart G3RXQ
>
>
>
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