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RE: RDS Question
To: CRTech <crtech@crtech.org>
Subject: RE: RDS Question
From: Alan Kilgore <wrvm.engineer@gmail.com>
Date: Fri, 22 Sep 2017 14:00:50 -0500
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The accuracy of a mod meter is diminished when not making measurements from the transmitter sample port due to noise, intermod and signals from other stations within quite a number channels from the one intended to be measured.

You can get reasonably close when the signal is sufficiently high and the multipath level is extremely low.

I know of a modulation war started by a Program Director a number of years ago. It was a small town rim-shot station that was broke and had more primitive processing than the bigger stations in that market. The PD had re-tuned the station's mod meter at the studio to a competitor's frequency and saw modulation readings higher than their own readings. Their transmitter was in a different direction than most of the other stations in the larger market. He did not realize the inaccuracy resulting from low signal and relatively high multipath of the competing station in their receiver. So, he would goose his own station's modulation to match their level, thinking that he had matched the competition in a loudness war that he perceived as being started by the other station. In reality, he had set his station to be much louder than the other stations, thereby actually starting a loudness war.

Some of the other market stations matched with their modulation increases and so that station's PD increased his again, thinking he was only matching the competition again. It went some number of cycles before the station PD called me wanting to know how much higher they could go without getting fined by the FCC and complained that they were having a hard time getting more loudness without causing distortion. I asked a few questions over the phone about the receiving antenna and modulation monitor model. I knew their rural studio was a rim-shot of the market. The facts added up for me to realize it was operator error.

So I made the trip into the market for more accurate field modulation measurements with my equipment. Then I showed the client how turning the receive antenna for the modulation monitor towards the station being measured caused their modulation meter to have lower peaks. The competition's signal in their modulation monitor came closer to matching what my equipment measured when receiving the signals acceptable for making approximate modulation measurements. Of course, with that antenna orientation, their own station showed even higher modulation due to multipath. So, the PD finally believed my explanation and allowed me to set their station's modulation properly. He also called someone at the competing station. I don'[t know what he told them, but I understand that it brought the loudness war back into a more nominal range.

So, when you measure the modulation of other stations or even your own, be certain that you understand the limitations when making distant measurements, including signal strength, multipath, terrain, other station signals and propagation issues.

Alan Kilgore, CPBE
WRVM Chief Engineer

At 08:59 AM 9/22/2017, you wrote:
Good you guys pay this much attention to rules and details. My portable modulation analyzer tuned to various stations while I’m driving around shows levels set all over the place, RDS, pilot, and total modulation. Pilots often not in range of 8 to 10 percent, etc.


Follow-Ups: RE: RDS Question
("Bill Hurne" <billhurne@pilgrimradio.com>, 22 Sep 2017 20:32:46 -0000)
Re: RDS Question
(Willie Barnett <wbradiolists@gmail.com>, 22 Sep 2017 23:42:11 -0000)
References: RDS Question
(Steve Tuzeneu <stuzeneu@gmail.com>, 22 Sep 2017 10:21:48 -0000)
RE: RDS Question
("John Graham" <john@wfcj.com>, 22 Sep 2017 12:43:31 -0000)
Re: RDS Question
(Kevin Kidd <kkbroadcastengineering@gmail.com>, 22 Sep 2017 13:31:05 -0000)
RE: RDS Question
("Bill Hurne" <billhurne@pilgrimradio.com>, 22 Sep 2017 13:59:46 -0000)
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