[ARC5] S+N/N ratio results.

[Glen Zook]

Not exactly!  Collins alignment procedures for receivers was pretty specific.  After signal generators became available with a true 50-ohm output, then the signal generator was connected directly to the receiver.  With older signal generators including the HP-606- series, Measurements 65, military TS-497- series, and so forth, that did not present a 50-ohm impedance over the entire coverage, a resistive network was connected between the signal generator output and the receiver.  The values of the resistors chosen formed a 6 dB pad.   The signal generator output (in microvolts) for an S-9 "S" meter reading was given as 100-microvolts.  However, this reading was before the 6 dB pad and, therefore, the actual signal level applied to the receiver for an S-9 reading was actually 50-microvolts.

For "field" alignment, when the crystal calibrator was used for the signal source, a 47-ohm resistor was to be inserted into the receiver antenna jack which "terminated" the input impedance to approximate a 50-ohm load.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: Geoff <geoffrey at jeremy.mv.com>
To: Roy Morgan <k1lky at earthlink.net>; Richard Knoppow <1oldlens1 at ix.netcom.com> 
Cc: ARC5 <arc5 at mailman.qth.net> 
Sent: Saturday, June 15, 2013 3:42 PM
Subject: Re: [ARC5] S+N/N ratio results.
 

I've read that the Collins lab procedure to check sensitivity was to hook 
the (50 ohm) generator output directly to the receiver with no terminating 
resistor or pad.  Included in what I read was the statement that the 
receivers had actual input impedances close enough to 50 ohms to make this 
work out right.

** Interesting, do you have any citations to that?

> ...   At any rate, getting an approximate measurement on a boat anchor is 
> possible.

Oh, good!  I'd rather not thing that all this is in vain.


**  Chuckle


> A meaningful measurement on a receiver with fractional microvolt 
> sensitivity is quite difficult.

I think that many reports of fractional microvolt sensitivity are suspect.

Roy

** Completely agree but easily accomplished over several decades now with 
proper procedures and equipment. For an ARC-5 it would be strictly a labor 
of love but since this group drifts all over the universe there are 
legitimate applications.