[Elecraft] Re: RFC15 &C91

[Denis Jackson]

Hi Don,

Thanks for this.  I can confirm that my problem was yet another 
manifestation of the open circuit RFC15 - although with a twist.  I found 
that I could only get stable performance by having the top cover on as well, 
then running CAL PLL. Running this routine without the top cover resulted in 
stability problems.

I will see if I can find a suitable replacement component in the UK 
otherwise I will have to order one form Elecraft.  I have shorted it out for 
now.

Sensitivity and signal/noise seems fine so as you suggested in your previous 
mail, I shall wait until I have finished building then either download the 
software you suggested or maybe even see if my ancient Rockland audio 
spectrum analyser still has any life in it!

Many thanks for helping to get me back on track.  Buying a K2 isn't just 
about buying a radio, it's also buying into a very special club that reminds 
me of how ham radio used to be when I first got interested more than 30 
years ago.

73

Denis


----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at embarqmail.com>
To: "Radio" <radio at modesgate.com>
Sent: Monday, October 22, 2007 9:12 PM
Subject: Re: RFC15 &C91


> Denis,
>
> Yes, you need all the covers except the top cover in place when running 
> CAL PLL - the counter needs to read the frequencies correctly as the PLL 
> Reference oscillator varactor voltages are being changed by the 
> microprocessor in order to interpolate correctly at the 5 kHz end points
>
> The RFC15/C91 change is part of the A to B mod.  I believe it may have 
> been mentioned earlier as part of the WAOF (weird at one frequency) 
> problem.  It is installed on all K2s above SN3000.  If installed, check 
> RFC15 for continuity with an ohmmeter (a voltage check at both ends does 
> not tell the right story - it will be 5 volts even if the choke is open).
>
> If you have a K2 with SN less than 3000, you should add it.
> To install it, you need a 100 uH RF choke and a .001 capacitor. You also 
> need to cut the trace that connects to pin 16 of U4 - RFC15 goes across 
> the trace cut and C91 connects from pin 16 to ground.
>
> 73,
> Don W3FPR
>
> Radio wrote:
>> Hi Don,
>>
>> I had a bit more time today to look through the archive and I found 
>> several references to tuning "chirps" and "warbles" which all seemed to 
>> be associated with either not having ALL the covers in place when running 
>> CAL PLL or, alternatively, connected with the RFC15/C91 modification from 
>> U4, pin 16.
>>
>> What is this modification for - I couldn't seem to find an explanation?
>>
>> 73
>>
>> Denis MW0CBC/GW8OQV
>>
>> ________________________________________________
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>
>