Elecraft

K2 : Is this ok for AGC threshold??

Classic

List

Threaded

4 messages Options

Fred Bennett N9TA-2

K2 : Is this ok for AGC threshold??

Hi Gang

Construction on my 3rd K2 is coming right along......BUT....I have a
question: I'm at page 48 of the manual where I am going through the
first power-up checks. I can't get the "AGC Threshold" voltage up to 3.8
Vdc as suggested. My new K2 tops out around 3.62 as measured with a
Square D WMM-23 digital multimeter. Is this something I should worry about??

73....de....Fred N9TA
K2 serial# 6705 under construction
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: K2 : Is this ok for AGC threshold??

Fred,

It is all relative. If the 8 volt regulator output is on the lower side
of its spec (it is a 10% tolerance part), then everything will work out
just fine, set it to the maximum.
Reason - the IF amplifier is the stage controlled by the AGC, *and* it
is powered by the 8 volt regulator. When the IF Amp supply voltage is
reduced, the ACG action begins at a lower voltage point than at higher
voltages.

Bottom line - if you are able to set the S-meter parameters with the
lower AGC Threshold voltage, then all is well. If you cannnot adjust
the S-meter, then a 10k to 15k resistor soldered across pins 3 and 4 of
Control Board RP6 will allow you to adjust the threshold upward.

Yes, a manual errata sheet should be published IMHO. The 3.8 volts is
not graven in stone. There is an implication in the K2 manual that the
AGC threshold can be optimized later on, but there are no details of how
to do that - in fact, that optimization is simply reducing the AGC
Threshold voltage so that receiver noise does not activate the AGC.

73,
Don W3FPR

Fred Bennett N9TA wrote:

> Hi Gang
>
> Construction on my 3rd K2 is coming right along......BUT....I have a
> question: I'm at page 48 of the manual where I am going through the
> first power-up checks. I can't get the "AGC Threshold" voltage up to 3.8
> Vdc as suggested. My new K2 tops out around 3.62 as measured with a
> Square D WMM-23 digital multimeter. Is this something I should worry about??
>
> 73....de....Fred N9TA
> K2 serial# 6705 under construction
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 8.0.237 / Virus Database: 270.11.8/1987 - Release Date: 03/06/09 07:20:00
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Fred Bennett N9TA-2

Re: K2 : Is this ok for AGC threshold??

Thanks for the quick reply Don !!!

I guess I will continue then.....I'd decided to stop further
construction until I had an answer. Just in case it was something to be
concerned about.

Gosh....seems like these components just get smaller and smaller....HI HI

73...de...Fred N9TA
_______________________________________________

Don Wilhelm wrote:

> Fred,
>
> It is all relative. If the 8 volt regulator output is on the lower
> side of its spec (it is a 10% tolerance part), then everything will
> work out just fine, set it to the maximum.
> Reason - the IF amplifier is the stage controlled by the AGC, *and* it
> is powered by the 8 volt regulator. When the IF Amp supply voltage is
> reduced, the ACG action begins at a lower voltage point than at higher
> voltages.
>
> Bottom line - if you are able to set the S-meter parameters with the
> lower AGC Threshold voltage, then all is well. If you cannnot adjust
> the S-meter, then a 10k to 15k resistor soldered across pins 3 and 4
> of Control Board RP6 will allow you to adjust the threshold upward.
>
> Yes, a manual errata sheet should be published IMHO. The 3.8 volts is
> not graven in stone. There is an implication in the K2 manual that
> the AGC threshold can be optimized later on, but there are no details
> of how to do that - in fact, that optimization is simply reducing the
> AGC Threshold voltage so that receiver noise does not activate the AGC.
>
> 73,
> Don W3FPR
>
> Fred Bennett N9TA wrote:
>> Hi Gang
>>
>> Construction on my 3rd K2 is coming right along......BUT....I have a
>> question: I'm at page 48 of the manual where I am going through the
>> first power-up checks. I can't get the "AGC Threshold" voltage up to
>> 3.8 Vdc as suggested. My new K2 tops out around 3.62 as measured with
>> a Square D WMM-23 digital multimeter. Is this something I should
>> worry about??
>>
>> 73....de....Fred N9TA K2
>> serial# 6705 under construction
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> ------------------------------------------------------------------------
>>
>>
>> No virus found in this incoming message.
>> Checked by AVG - www.avg.com Version: 8.0.237 / Virus Database:
>> 270.11.8/1987 - Release Date: 03/06/09 07:20:00
>>
>>
>

WE0H

Re: K2 : Is this ok for AGC threshold??

Hi Fred,

I ran into that regulator issue a couple nights ago. I changed the 8v
regulator with a used one I had here which brought the 8v line up to
8.30v. The original 8v regulator put out 7.61v. My AGC pot is a half
scale right now with the 3.80v level as the manual states. The resistor
mod takes care of the issue if you don't have a spare regulator laying
around.

Mike
WE0H

Fred N9TA wrote:
> Thanks for the quick reply Don !!!
>
> I guess I will continue then.....I'd decided to stop further
> construction until I had an answer. Just in case it was something to be
> concerned about.
>
> Gosh....seems like these components just get smaller and smaller....HI HI
>
> 73...de...Fred N9TA
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html