Signal Measurement for IBOC and Non-IBOC Signals?

[Mark_Ericson]

Hello:

I am a high school student who is in an advanced program called the Governor's School. In it, I take a collection of dual-enrollment (high school and college credit) classes. However, one of the requirements is a symposium project, scientific in nature, to last roughly a year and a half and present to a large group of people.

I wanted to do a comparison of analog signal strength of FM with and without IBOC, a before-and-after type of affair. Seeing as how AM signals get a background hiss in the analog signal from IBOC, I want to see if FM does the same thing or will even reduce coverage, as stereo does.

The only problem is, my instructors and I have no idea how to measure such a thing. Any idea?

Thanks. Any help is most appreciated.

- Trip<P ID="signature">______________
Visit my website, www.rabbitears.info! It's eventually going to be your one resource for television info! Digital television, histories, and technical information for the entire USA from one source!</P>

 

[eastsidah]

>
I'm not an expert, but as no one else has answered you I'll throw in my understanding...

There is a big difference between FM IBOC and FM Analog Signal strengths...or at least transmitter output. A Fraction of the power is needed for an IBOC signal to cover the same ground as its analog companion. I have not heard any interference on the analog side of an IBOC equipped station...KBKS in Seattle is a great example, great Analog signal, great IBOC signal, few if any problems on the adajacent channels...

AM IBOC is a different story..it's a bad thing.
Hello:
>
> I am a high school student who is in an advanced program
> called the Governor's School. In it, I take a collection of
> dual-enrollment (high school and college credit) classes.
> However, one of the requirements is a symposium project,
> scientific in nature, to last roughly a year and a half and
> present to a large group of people.
>
> I wanted to do a comparison of analog signal strength of FM
> with and without IBOC, a before-and-after type of affair.
> Seeing as how AM signals get a background hiss in the analog
> signal from IBOC, I want to see if FM does the same thing or
> will even reduce coverage, as stereo does.
>
> The only problem is, my instructors and I have no idea how
> to measure such a thing. Any idea?
>
> Thanks. Any help is most appreciated.
>
> - Trip
>

 

[nd2023]

You will need a field strength meter, and probably the cooperation of a few IBOC stations to test the difference in analog signal strength.

I have noticed that the strength is nearly the same before and after IBOC when some local stations got IBOC.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471
WWPH 107.9 FM: http://wwph1079fm.no-ip.org</P>

 

[Mark_Ericson]

> You will need a field strength meter, and probably the
> cooperation of a few IBOC stations to test the difference in
> analog signal strength.
>
> I have noticed that the strength is nearly the same before
> and after IBOC when some local stations got IBOC.

Yes, I don't know what to use to MEASURE that signal strength. I need something to measure with other than my ears.

I figure I'll find a station and do signal tests before and after IBOC.

- Trip<P ID="signature">______________
Visit my website, www.rabbitears.info! It's eventually going to be your one resource for television info! Digital television, histories, and technical information for the entire USA from one source!</P>

 

[CW]

> Yes, I don't know what to use to MEASURE that signal
> strength. I need something to measure with other than my
> ears.
>
> I figure I'll find a station and do signal tests before and
> after IBOC.
>
> - Trip

Becasue of the nature of IBOC in the hybrid mode where it is outside the analog passband, you cannot use a normal field strength meter to read the digital signal. It's not selective enough. What you must use is a spectrum analyzer and look at the RF mask of the overall signal....the analog will be in the center and the digital is on the outside....There is no other way to measure the digital signal...analog can be read by a simple signal strength meter in an FM radio...but for quantified readings with some numbers attached that mean something, a spectrum analyzer with a calibrated antenna would have to be used.
The analog signal in either case is not changed whatsoever...and because of the bandwidth of FM and the action of a FM radio limiter stage, you do not have the hash noise on IBOC FM like you do on AM!

 

[nd2023]

Forget about the field strength meter, just get a few gallons of gas. You could drive away from a transmitter with and without IBOC and compare the range. The measured quantity would be miles away from the transmitter.

Of course, this is one of the most inaccurate ways to measure strength because terrain and tropo ducting could affect the range.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471
WWPH 107.9 FM: http://wwph1079fm.no-ip.org</P>

 

[k9ez]

> You will need a field strength meter, and probably the
> cooperation of a few IBOC stations to test the difference in
> analog signal strength.
>
> I have noticed that the strength is nearly the same before
> and after IBOC when some local stations got IBOC.
>


HD signals should haev no effect on the analog signal as typcailly they use different trasnsmitters.

A good way to measure the HD signal is an Audemat Golden Eagle monitoring unit.

 

[_Jim]

> Forget about the field strength meter, just get a few
> gallons of gas. You could drive away from a transmitter
> with and without IBOC and compare the range. The measured
> quantity would be miles away from the transmitter.
>
> Of course, this is one of the most inaccurate ways to
> measure strength because terrain and tropo ducting could
> affect the range.
>

Quote: "drive away from the transmitter [site] ... one
of the most inaccurate ways"

Unless - one built some 'pads' (literally: "attenuator pads")
and used these in way to provide reliable attenuation
to an otherwise strong signal.

'Pads' are used in industry very often during testing,
to artificially reduce the signal strength when placed
in-line with a receiver's antenna input.

Using an assortment of 'pads' one could guage how much
better one signal or receiver did over another, based
on how much attenuation began to offer a weak or noisy
signal or cause digital to 'drop out' or revert to analog.

Pads are usually comprised of a three resistor in a pi or T
configuration. There are web-based CGI and JavaScript
pages that can provide you the resistor vales required
given your system impedance (probably 75 Ohms for an
FM receiver) and the required atenuation value (like
10 dB, 20 dB and so on.)