[Elecraft] An AGC story

[Joe Subich, W4TV]

 > Very interested findings -  Fred has a graph of AGC action with AGC
 > THR=8 labeled figure 3 on http://www.ke7x.com/home/the-k3-agc-story  :

That graph is nearly identical to the information that Jack Smith,
K8OZA originally presented two years ago:
   http://cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm

The following table comes from Jack's work:

 > From the data, my estimate of the threshold settings is:
 >
 >    AGC THR    Corresponding Input
 >               Signal Level
 >      2          -117   dBm
 >      3          -110.5 dBm
 >      4          -105   dBm
 >      5          -103.5 dBm
 >      6          -102.5 dBm
 >      7          -101   dBm
 >      8           -99   dBm

The K2 AGC curve is also presented for comparison.  K2 does not
have a well defined threshold like that of the K3 but some AGC
action (the curve departs from 1:1) begins at around -85 dBm and settles 
at slope similar to the K3 SLP=09 or SLP=10 (about 1.5 dB
audio change for 10 dB RF change) at an RF level around -70 dBm.

As a second point of comparison, Sherwood's Receiver Performance Table
shows the FT-1000D has an AGC threshold nearly 10 dB higher than the
K3 *with the FT-1000D preamplifier enabled*.  Since the FT-1000D
preamp is at least 10 dB, that represents an overall 20 dB higher
ACG threshold (around S8/S9 with preamp off and S6/S7 with preamp on).

It seems clear that the K3 would have much better "pile-up performance"
if range of AGC THR were expanded by as much as 20 dB either by
increasing the "step" (5/6 differ by only 1 dB) or by increasing
the number of options.

73,

    ... Joe, W4TV

On 12/9/2010 9:07 AM, Barry N1EU wrote:
>
>
> Cady, Fred wrote:
>>
>> I made some measurements and have posted the results for your perusal
>> and information at www.ke7x.com.
>>
> Very interested findings -  Fred has a graph of AGC action with AGC THR=8
> labeled figure 3 on http://www.ke7x.com/home/the-k3-agc-story  :
>
> So I ask this group: is it possible to raise the AGC Threshold from s3 to s6
> or s9 by simply reducing the RF Gain control?  Can anybody estimate what
> settings of the RF Gain control would accomplish that?
>
> Barry N1EU
>