[ARC5] Quick sensistivity comparison

[Bob Moody]

Generator leakage can make it difficult or impossible to accurately measure down below about 5. microvolts.  After you tune your signal generator to exact frequency, remove the frequency counter lead AND COVER THE UNCALIBRATED OUTPUT WITH AN APPROPRIATELY SHIELDED CAP.  (This is why the venerable H-P 608D has that BNC cap on the dangly chain at the "Uncalibrated Output" BNC connector.)  If left connected to the counter this lead can radiate several microvolts.  If just left uncapped a few microvolts can still escape.  When properly capped interference is way below .1 microvolt.  

Technicians using good bench set-up technique can routinely measure down to and below .1 microvolt, as did Ken and Glenn in the above thread.  If, on the other hand, you've turned the attenuated output signal all the way down and the receiver "still hears just fine", look for generator leakage.

Bob   K7IRK
Tillamook, Oregon        



----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Glen Zook" <gzook at yahoo.com>
Cc: "ARC5" <arc5 at mailman.qth.net>
Sent: Thursday, June 13, 2013 10:42 AM
Subject: Re: [ARC5] Quick sensistivity comparison


On 13 Jun 2013 at 10:04, Glen Zook wrote:

> Actually, tube-type ("valve") receivers routinely give better LDS /
> MDS (least descernable signal / minimum descernable signal) signals
> than solid-state equipment. Things like phase noise are definitely
> higher in "modern" solid-state equipment. Now, generally for
> operation on MF and HF, the ambient noise levels on the bands negate a
> lot of the LDS / MDS. That is, the noise level is often substantially
> above the weakest signal that the receiver is capable of receiving.
> As such, the improved sensitivity is not needed when an antenna is
> connected to the receiver.
> 
> I routinely get LDS / MDS level of well under 0.1 microvolt (and the
> leakage from the generator is extremely low) on receivers like the
> Collins S-Line, Heath SB-Line, Drake 4-Line, etc. Even on general
> coverage receivers like the HQ-140X, SX-100, etc., the LDS / MDS is
> often below 0.1 microvolt. Glen, K9STH

Thank you, Glenn. :-)

Ken W7EKB
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