[Elecraft] K3 Buffer Mod

[Jack Smith]

Larry's LP-PAN uses my Z10000 amplifier design in its front end, with a 
couple of modifications to provide variable gain.

The AD8007 amplifier chip in both my Z10000 and the LP-PAN is a decent 
amplifier with a respectable noise figure.

If the K3's IF sample circuit had been built with closer to 0 dB 
transfer gain, then the composite noise figure would be closer to the 
K3's noise figure.

To answer the two questions directly (I don't have an LP-PAN, so Larry 
might wish to modify my answers):

1. Is the mod necessary with the LP-PAN, or is it only needed with other
panadapters? That is, is the noise figure of the LP-PAN's internal amplifier
sufficient, or is the mod to the K3 required to lift weak signals above the
noise floor of the LP-PAN?

I believe you will see a small improvement in composite K3-LP-PAN noise 
figure if the changes are made to the K3's IF sample circuitry. However, 
I doubt that under most band conditions you will observe a difference as 
there is sufficient external noise to mask the improvement.

2. Would the external buffer amplifier solution be a viable alternative to
the mod?

Yes, I believe it is if you are using something other than the LP-PAN as 
the panadapter. Panadapters are not normally designed to be as sensitive 
as a receiver. There are many reasons for that that I won't bother to go 
over now. The consequence is that designers of receivers that provide a 
pan scope RF sample have the levels set so that there is at least a net 
0 gain, and positive gains of 10 dB or more are not uncommon. I'm 
speaking mostly of commercial and military grade equipment, but my 
Kenwood TS-940 has reasonable transfer gain as well.


Jack K8ZOA
www.cliftonlaboratories.com


Richard Ferch wrote:
> I am scratching my head wondering whether any of this applies to the LP-PAN,
> or whether it is only relevant to other panadaptors such as the Softrock and
> the Z90.
>
> K8ZOA's web page (the same one everyone is quoting) says:
>
> "I looked at two potential panadapters; a Softrock and my Z90.
> (Telepostinc's LP-PAN has a built-in amplifier to overcome the transfer gain
> problem.)"
>
> and in the recommendations near the bottom of the page, refering to the mod,
>
>
> "These steps are not necessary with an LP-PAN panadapter as it has a
> built-in isolation amplifier."
>
> That same web page also suggests that an alternative to the mod would be to
> use an external buffer amplifier.
>
> So, I have two questions:
>
> 1. Is the mod necessary with the LP-PAN, or is it only needed with other
> panadapters? That is, is the noise figure of the LP-PAN's internal amplifier
> sufficient, or is the mod to the K3 required to lift weak signals above the
> noise floor of the LP-PAN?
>
> 2. Would the external buffer amplifier solution be a viable alternative to
> the mod?
>
> 73,
> Rich VE3KI
>
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