[K3] [Elecraft] Problems with K3 KXV3 IF Output Level?

Bill W4ZV btippett at alum.mit.edu
Thu Jul 31 07:24:01 EDT 2008




Fern Rivard wrote:
> 
> Good evening Lyle:
> 
>     I honestly don't know where you're getting those levels from as I
> already reported to you back in April/08 that the levels at the I F output
> were pretty well non existent. There is just no tracking of levels at the
> I F out with what is fed into the antenna input of the receiver. I even
> used a 15 db amplifier from Jack Smith of Clifton Laboratories without any
> luck as there is simply no levels to play with there. I believe that Jack
> Smith also queried you about that without getting a proper reply as yet
> from you. I realize that nobody is perfect but why are we dogging a proper
> reply and/or fix for that?
>     Fern with K3  #412
> 

See N8LP's comments below.  My IF OUT level improved ~7.5 dB with his mod
which involves changing R8 to 15k and R9 to 50 ohms on the K3 RF Board.  

73,  Bill

Re: [LP-PAN] Re: K3 IF output

The NF of LP-PAN by itself is the same as the K3 with preamp off. A
signal at about -127dBm (0.1uV) can be heard about equally well with 500
Hz filter above the noise floor of about -135dBm. But the overall NF of
LP-PAN depends on the K3. This is because the losses in the K3 mixer /
internal buffer add to the NF. In a stock K3, these losses add up to
about 17dB. Turning the K3 preamp on helps a lot, since the preamp has
low NF and adds gain ahead of the losses, where it has a greater effect
on the overall NF.

The simple mod I did to my K3 internal buffer reduces the losses by
almost 10dB, while only reducing the IP3 of the system by a couple dB.
My modified K3 / LP-PAN combo has an overall NF that is below
atmospheric noise here on all bands but 10m... with the K3 preamp off.
This seems to me to be a reasonable balance of signal handling and
sensitivity. Turning the K3 preamp on, without the mod, produces a
similar result as I recall. Unless you regularly see signals above
-20dBm, leaving the K3 preamp on should not be a problem. I haven't seen
a signal that strong here yet, even during FD where I had two stations
within a mile of my QTH.

I haven't heard anything more from Wayne about the possibility of a
running change in the K3 circuit, but the mod is simple to do if you
like. It's changing two resistors (actually one can be paralleled to the
existing one), similar to doing the HAGC mod. Several users have done it.

73,
Larry N8LP

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