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Do 1-5 Analog Signal Strength Meters compare to 1-5 mV/m???

T

Tom_

Guest
Analog signal strength meters on older radios including some portable ones consist of a dial with units of 0 to 5, and beyond to infinity...

Is there a relationship between 0,1,2,3,4,5 for AM and the field strength in mV/m???

It would be my guess that if the dial swings all the way to the top (infinity) then that means you are 5mV/m or greater...

and that 4 corresponds to 4mV/m, 3 to 3, etc. etc...

Is this correct?

For FM it gets tricky, since the unit I use gives a reading of 5 for a local signal, yet with batteries it's 4 for a local signal.

On AM, there is no decrease in the reading with DC vs. AC.

BTW - note the new FCC web site pattern data including PDF diagrams for AM stations!!!
 
> Analog signal strength meters on older radios including some
> portable ones consist of a dial with units of 0 to 5, and
> beyond to infinity...
>
> Is there a relationship between 0,1,2,3,4,5 for AM and the
> field strength in mV/m???
>
> It would be my guess that if the dial swings all the way to
> the top (infinity) then that means you are 5mV/m or
> greater...
>
> and that 4 corresponds to 4mV/m, 3 to 3, etc. etc...
>
> Is this correct?
>
> For FM it gets tricky, since the unit I use gives a reading
> of 5 for a local signal, yet with batteries it's 4 for a
> local signal.
>
> On AM, there is no decrease in the reading with DC vs. AC.

Signal-strength meters of any kind just measure the AGC voltage. Yours is just numbered arbitrarily and probably doesn't correspond to actual voltage. You'd have to connect a DVM to the same point that the analog meter is connected to in order to get the actual voltage.

"Calibrated" S-meters are even worse. A level of S-9 is supposed to mean a 50 uV signal strength, with each S-number below it being a 6 dB-lower signal. In truth, what is measured with the meter at S-9 varies with frequency due to the imperfect circuits in the radio, especially older ones. Each radio is different.
 
Re: New AM pattern info on FCC site

> BTW - note the new FCC web site pattern data including PDF
> diagrams for AM stations!!!

Yes, it's good to see that they added them, but you have to really enlarge them to see the real shape of things. Of course it would be nice if the AM patterns were shown on maps like on the FM query, but that may never happen.

www.fcc.gov/mb/audio/amq.html
 
Re: How does one build a spectrum analyzer?

Thanks for the info!

How does one build a spectrum analyzer - or something to connect to the signal strength meter as you mention below....any kits for building these on the internet?




> > Analog signal strength meters on older radios including
> some
> > portable ones consist of a dial with units of 0 to 5, and
> > beyond to infinity...
> >
> > Is there a relationship between 0,1,2,3,4,5 for AM and the
>
> > field strength in mV/m???
> >
> > It would be my guess that if the dial swings all the way
> to
> > the top (infinity) then that means you are 5mV/m or
> > greater...
> >
> > and that 4 corresponds to 4mV/m, 3 to 3, etc. etc...
> >
> > Is this correct?
> >
> > For FM it gets tricky, since the unit I use gives a
> reading
> > of 5 for a local signal, yet with batteries it's 4 for a
> > local signal.
> >
> > On AM, there is no decrease in the reading with DC vs. AC.
>
>
> Signal-strength meters of any kind just measure the AGC
> voltage. Yours is just numbered arbitrarily and probably
> doesn't correspond to actual voltage. You'd have to connect
> a DVM to the same point that the analog meter is connected
> to in order to get the actual voltage.
>
> "Calibrated" S-meters are even worse. A level of S-9 is
> supposed to mean a 50 uV signal strength, with each S-number
> below it being a 6 dB-lower signal. In truth, what is
> measured with the meter at S-9 varies with frequency due to
> the imperfect circuits in the radio, especially older ones.
> Each radio is different.
>
 
Re: How does one build a spectrum analyzer?

> Thanks for the info!
>
> How does one build a spectrum analyzer - or something to
> connect to the signal strength meter as you mention
> below....any kits for building these on the internet?

A spectrum analyzer is used for different purposes. It's generally used to measure transmitters, checking for power output, spurs, harmonics, and the like. It can also be used as a receiver to measure the field strength of a transmitter/antenna at a given distance, mostly to keep the FCC happy or to tune the antenna properly. It wouldn't be used as a received signal-strength indicator.

There are simple spectrum analyzers available that attach to oscilloscopes or PC sound cards. Many of these are based on TV tuner modules. A Google search should find these, or look in old QST Magazines. There have been several published in the last 10 years.

But this doesn't sound like that's what you're looking for. Really, an S-meter is overrated as a receiver accessory. It's useful as a tuning indicator, but as long as you can hear a station, then it really doesn't matter what its signal strength is.
 
Re: How does one build a spectrum analyzer?

What I'd like to get is something to measure AM frequency signal strength in mV/m when I'm travelling...and also try to guess the pattern and then plot it if I don't already know the pattern...

And...something in uV/m for LPFM...

But maybe these units are too expensive...

I have yet to research this on the web further...and many of the technical terms you mention I will look up...

It's really fun to travel and measure AM patterns with the new FCC signal maps at the AM query page!

Thanks again...

> > Thanks for the info!
> >
> > How does one build a spectrum analyzer - or something to
> > connect to the signal strength meter as you mention
> > below....any kits for building these on the internet?
>
> A spectrum analyzer is used for different purposes. It's
> generally used to measure transmitters, checking for power
> output, spurs, harmonics, and the like. It can also be used
> as a receiver to measure the field strength of a
> transmitter/antenna at a given distance, mostly to keep the
> FCC happy or to tune the antenna properly. It wouldn't be
> used as a received signal-strength indicator.
>
> There are simple spectrum analyzers available that attach to
> oscilloscopes or PC sound cards. Many of these are based on
> TV tuner modules. A Google search should find these, or
> look in old QST Magazines. There have been several
> published in the last 10 years.
>
> But this doesn't sound like that's what you're looking for.
> Really, an S-meter is overrated as a receiver accessory.
> It's useful as a tuning indicator, but as long as you can
> hear a station, then it really doesn't matter what its
> signal strength is.
>
 
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