Re: {Collins} KWM-2 Receiver sensitivity check.

[kkeller1@xxxxxxxxxxx]

Just some additional information on the KWM2/2A in regards to the S meter. The means of calibrating this at the factory was 

by test selecting a resistor. If you check the schematic you will see this resistor noted as a test select one.  It is easy to find 

because it goes across the top of one of the connection trees as I call them. I have found that if a calibrator is giving 10 to 20 

over S9 on 20 meters with the calibrator and with a dummy load on the antenna it is a good indication the meter is reading 

somewhat correctly. 



I have changed out this resistor with a different value in many units to get the meter reading correctly using a signal 

generator set as mentioned below. This was done of course after all weak tubes were replaced and the unit was aligned. Keep 

in mind since it was set at the factory a lot of components have changed  their characteristics and you are using different tubes 

which explains why you need to change the value of the resistor. 



Kurt Keller 








----- Original Message ----- 
From: "Glen Zook" <gzook@xxxxxxxxx> 
To: collins@xxxxxxxxxxxxx, "Bent" <bjoe@xxxxxxxxxxxxx> 
Sent: Saturday, October 17, 2009 3:29:01 PM GMT -05:00 US/Canada Eastern 
Subject: Re: {Collins} KWM-2 Receiver sensitivity check. 

You can do a pretty good field alignment with the crystal calibrator.  However, you really need a signal generator with a calibrated attenuator to really get a reliable reading on the actual sensitivity. 

At present I have a 75S-3A and two 75S-1 receivers and used to have another 75S-3.  All of them have pretty close to the same sensitivity when checked with a station monitor ("fancy" signal generator, etc.) yet the "S" meter readings are considerably different.  They are adjusted for 50 microvolts = S-9.  However, as the frequency increases the output from the crystal calibrator is different among the receivers. 

I know that there are some "relative" signal level readings from the crystal calibrator out there.  But, they really don't tell you much as to what the actual sensitivity of the receiver is. 

Unfortunately, when you replace all of the tubes in a receiver the alignment is often "way off".  Remember, tubes last for decades and it usually is not considered prudent to replace all of the tubes just to replace them. 

Glen, K9STH 

Website:  http://k9sth.com 


--- On Sat, 10/17/09, Bent <bjoe@xxxxxxxxxxxxx> wrote: 

I would like to check the receiver sensitivity on my KWM-2. 
  
I hope I can do it by help of the crystal calibrator. Are someone able to inform me about the S-meter level on all "old" 5 bands when the crystal calibrator is ON. 
  
Are there some special things I have to do when using the crystal calibrator as receiver tester ? 
  
I have just installed new tubes in the KWM-2, but not impressed about receiver performance. 


       
_______________________________________________ 
SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY ! 
http://www.collinsradio.org/membership/ 


 NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific 
  SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central 
  1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)