[Elecraft] [K3] K3 output buffer modification

[Jack Smith]

The LP-Pan has an AD 8007 input amplifier, the same amplifier I use in 
the Z10000 buffer amp.

In the LP-Pan, the AD8007's gain is set by a combination of fixed 
resistors and a potentiometer. Quickly working through the numbers, 
varying the potentiometer from one end to the other results in gain 
ranging from +6 dB to +15 dB, net of the 6 dB loss in the series 49.9 
ohm resistor. (Measured at the AD8007's output pin, the  gain is 6 dB 
above these values, but in order to drive a capacitive load, a series 
49.9 ohm resistor is added between the output pin and the load. This 
results in 6 dB loss if the load is 50 ohms.)

The main reason one might wish to apply the buffer modification to the 
K3 instead of cranking up the LP-Pan gain or purchasing one of my Z10000 
buffer amplifiers is that a somewhat improved noise figure will result 
if the K3's IF output follower loss is reduced. In practice, the 
improvement in noise figure is not huge as the overall NF is set mostly 
by the early gain stages in the K3.

Jack K8ZOA




On 1/7/2010 12:32 PM, Bill W4ZV wrote:
>
>
> Bill W4ZV wrote:
>    
>> An unmodified K3's IF OUT has 7-17 dB transfer loss that cannot be
>> compensated for in ANY panadaptor, so the mod is necessary for the P3.
>>
>> http://cliftonlaboratories.com/elecraft_k3_and_panadapters.htm#What_then_is_the_transfer_gain_of_the_K3_
>>
>>      
> Jack Smith's comment on the page above "Telepostinc's LP-PAN has a built-in
> amplifier to overcome the transfer gain problem." is incorrect.  LP-PAN
> **DOES** require the mod and N8LP posted a mod similar to Elecraft's back in
> July 2008.
>
> http://groups.yahoo.com/group/LP-PAN/files/K3_Buffer_Mod/
>
> 73,  Bill
>