[Hammarlund] S meter

[kirklandb at sympatico.ca]

The math behind 3 dB v 6 dB isn't terribly hard.

 dBs are deci "Bels" and used to measure power ratios
 Power Gain/attenuation  = 10 log10 (P1/P2)

Many times we work with voltages. As long as the Load
 resistance remains the same, we can express power gains
 with just voltage ratios (or current).  P = V^2/R
  Power Gain = 10 log10 ( V1^2/R  / [V2^2/R]), the R's cancel leaving
             = 10 log 10 (V1^2/V2^2), which simplifies to
             = 20 log 10 (V1/V2)

 hence doubling the voltage into a given load quadruples the power
   i.e. 6 dB power increase.

In the good old days, I remember my heathkit (oops Hammarlund) receivers being spec'd at 0.35 uV.

Most modern receivers work in to 50 ohms and we talk about sensitivity interms of dBm not uV.  There is a significant
difference between 0.35 uV into 50 ohms and 0.35 uV into 600 ohms.

Most modern signal generators are 50 ohms out. Many old receivers
 that have high input impedances, and folks have found that they
  benefit from the use of 1:4 balun.

Bill, ve3jhu

> 
> From: Glen Zook <gzook at yahoo.com>
> Date: 2006/07/13 Thu AM 09:31:22 EST
> To: Mike Taylor <reel2reel at hotmail.com>,  hammarlund at mailman.qth.net
> Subject: Re: [Hammarlund] S meter
> 
> Doubling in power represents 3 dB.  Doubling in signal
> strength (voltage) = 6 dB.
> 
> When I get my website fully up again there is an
> article on there explaining the mathematics behind
> this.
> 
> Glen, K9STH
> 
> 
> --- Mike Taylor <reel2reel at hotmail.com> wrote:
> 
> Well Ken, I stand corrected. If I remember correctly,
> a doubling in signal strength is 3db. This in fact
> means that the meter on the HQ129-X is in fact a real
> and calibrated S meter, although not the type that
> we're used to today. I'd still like to know who
> invented the modern day S meter and if Hammarlund had
> anything to do with that. Thanks for the interesting
> reply.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Glen, K9STH
> 
> __________________________________________________
> Do You Yahoo!?
> Tired of spam?  Yahoo! Mail has the best spam protection around 
> http://mail.yahoo.com 
> _______________________________________________
> List Administrator: Duane Fischer W8DBF
> ** For Assistance: dfischer at usol.com **
> ----
> http://mailman.qth.net/mailman/listinfo/hammarlund
>