I have a very small understanding of the technical work involved in transmitting and such. I remember stumbling across an FM booster in the listings for Louisville area radio stations for WGZB 96.5 FM. It's main transmitter is located in Corydon, IN, but then there is a listing for a booster much closer to the metro area of Louisville. How does a booster work? How does the booster not interfere with the main signal transmitter? Just some curiosities I have. Thanks.
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FM Boosters
- Thread starter collegeDJ86
- Start date
> I have a very small understanding of the technical work
> involved in transmitting and such. I remember stumbling
> across an FM booster in the listings for Louisville area
> radio stations for WGZB 96.5 FM. It's main transmitter is
> located in Corydon, IN, but then there is a listing for a
> booster much closer to the metro area of Louisville. How
> does a booster work? How does the booster not interfere
> with the main signal transmitter? Just some curiosities I
> have. Thanks.
>
An FM booster operates on the same frequency as the primary channel and receives the audio through other means than over the air (because that would be impossible). A booster does interfere with the main signal, but it is not noticed since both signals carry the exact same audio information.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471</P>
> involved in transmitting and such. I remember stumbling
> across an FM booster in the listings for Louisville area
> radio stations for WGZB 96.5 FM. It's main transmitter is
> located in Corydon, IN, but then there is a listing for a
> booster much closer to the metro area of Louisville. How
> does a booster work? How does the booster not interfere
> with the main signal transmitter? Just some curiosities I
> have. Thanks.
>
An FM booster operates on the same frequency as the primary channel and receives the audio through other means than over the air (because that would be impossible). A booster does interfere with the main signal, but it is not noticed since both signals carry the exact same audio information.<P ID="signature">______________
17-year-old radio geek
Location: Princeton Junction, NJ
AIM: KewlDude471</P>
> > I have a very small understanding of the technical work
> > involved in transmitting and such. I remember stumbling
> > across an FM booster in the listings for Louisville area
> > radio stations for WGZB 96.5 FM. It's main transmitter is
>
> > located in Corydon, IN, but then there is a listing for a
> > booster much closer to the metro area of Louisville. How
> > does a booster work? How does the booster not interfere
> > with the main signal transmitter? Just some curiosities I
>
> > have. Thanks.
> >
> An FM booster operates on the same frequency as the primary
> channel and receives the audio through other means than over
> the air (because that would be impossible). A booster does
> interfere with the main signal, but it is not noticed since
> both signals carry the exact same audio information.
>
The signals would beat with each other because each transmitter would not be on the same EXACT freq. This is done by timing both (or more) to GPS. The second problem is the propagation delay both signals have to a spicific RX point. This is accomplished by delaying one transmitters audio ( by ms) so that the audio is in phase at the point where the two signals are at there equal level. Harris syncrocast equipment works well.
The problem is if there is a reception site that can "hear" both sites outside of the common area between both transmitters, the audio will be received out of phase. Depending on how far out of phase the audio is, will depend on how poor the audio will be.
This is a very basic explanation, but I think you get the idea.
> > involved in transmitting and such. I remember stumbling
> > across an FM booster in the listings for Louisville area
> > radio stations for WGZB 96.5 FM. It's main transmitter is
>
> > located in Corydon, IN, but then there is a listing for a
> > booster much closer to the metro area of Louisville. How
> > does a booster work? How does the booster not interfere
> > with the main signal transmitter? Just some curiosities I
>
> > have. Thanks.
> >
> An FM booster operates on the same frequency as the primary
> channel and receives the audio through other means than over
> the air (because that would be impossible). A booster does
> interfere with the main signal, but it is not noticed since
> both signals carry the exact same audio information.
>
The signals would beat with each other because each transmitter would not be on the same EXACT freq. This is done by timing both (or more) to GPS. The second problem is the propagation delay both signals have to a spicific RX point. This is accomplished by delaying one transmitters audio ( by ms) so that the audio is in phase at the point where the two signals are at there equal level. Harris syncrocast equipment works well.
The problem is if there is a reception site that can "hear" both sites outside of the common area between both transmitters, the audio will be received out of phase. Depending on how far out of phase the audio is, will depend on how poor the audio will be.
This is a very basic explanation, but I think you get the idea.
Since I have one ( a booster, that is) I can elaborate.
Boosters work well in hill country where you have an area that's blocked by the hills from the main station. The trick is to throw the interference zone into an area where there is little population (if possible).
They can be fed off air, the trick is to put the receiver on one side of ahill, beat it down to 10.7 mHZ, run it through a loooooong cable, then beat it back up to the transmitting frequency. We did it that way until the cable went bad, then switched to an STL feed.
Neat trilck if terrain allows.
Boosters work well in hill country where you have an area that's blocked by the hills from the main station. The trick is to throw the interference zone into an area where there is little population (if possible).
They can be fed off air, the trick is to put the receiver on one side of ahill, beat it down to 10.7 mHZ, run it through a loooooong cable, then beat it back up to the transmitting frequency. We did it that way until the cable went bad, then switched to an STL feed.
Neat trilck if terrain allows.
F
FredH
Guest
> Since I have one ( a booster, that is) I can elaborate.
>
> Boosters work well in hill country where you have an area
> that's blocked by the hills from the main station. The trick
> is to throw the interference zone into an area where there
> is little population (if possible).
>
> They can be fed off air, the trick is to put the receiver on
> one side of ahill, beat it down to 10.7 mHZ, run it through
> a loooooong cable, then beat it back up to the transmitting
> frequency. We did it that way until the cable went bad,
> then switched to an STL feed.
>
> Neat trilck if terrain allows.
>
Could you please eleborate on what you mean by 'beat it down to 10.7mhz'?<P ID="signature">______________
-I miss the old Rock 101</P>
>
> Boosters work well in hill country where you have an area
> that's blocked by the hills from the main station. The trick
> is to throw the interference zone into an area where there
> is little population (if possible).
>
> They can be fed off air, the trick is to put the receiver on
> one side of ahill, beat it down to 10.7 mHZ, run it through
> a loooooong cable, then beat it back up to the transmitting
> frequency. We did it that way until the cable went bad,
> then switched to an STL feed.
>
> Neat trilck if terrain allows.
>
Could you please eleborate on what you mean by 'beat it down to 10.7mhz'?<P ID="signature">______________
-I miss the old Rock 101</P>
> > They can be fed off air, the trick is to put the receiver
> on
> > one side of ahill, beat it down to 10.7 mHZ, run it
> through
> > a loooooong cable, then beat it back up to the
> transmitting
> > frequency. We did it that way until the cable went bad,
> > then switched to an STL feed.
> >
> > Neat trilck if terrain allows.
> >
> Could you please eleborate on what you mean by 'beat it down
> to 10.7mhz'?
Is the downconversion to avoid attenuation in the long cable?
> on
> > one side of ahill, beat it down to 10.7 mHZ, run it
> through
> > a loooooong cable, then beat it back up to the
> transmitting
> > frequency. We did it that way until the cable went bad,
> > then switched to an STL feed.
> >
> > Neat trilck if terrain allows.
> >
> Could you please eleborate on what you mean by 'beat it down
> to 10.7mhz'?
Is the downconversion to avoid attenuation in the long cable?
It's essentially a TEPCO (or Jones, same design) translator.
Crystal controlled receiver, with local oscillator 10.7 above or below receive frequency, mixer circuit, and the 10.7 signal then amplified, as in a typical FM receiver. However, instead of detecting the FM signal, the 10.7 IF signal is then coupled into a crystal controlled transmitter, where the IF signal is mixed again with the local oscillator to derive the new signal on a different carrier frequency, then amplfied.
With a booster the receive and transmit frequencies are the same. The problem, of course, then becomes the contamination of the receive signal by the much stronger transmit signal. Hence the receiver is placed in a sheltered location, then using the intermediate 10.7 mhz frequency, sent by the long cable to the booster's transmitting amplifier. There it is beat against another crystal oscillator to upconvert from 10.7 to the operating frequency. As noted, there is much less attenuation at 10.7 mhz then at the FM band; and it is also easy to build traps at both ends to keep FM band signals from being couple from one unit to the other. Usually the cable is buried to prevent the shield from coupling booster signal back into the receiver.
As can be seen, whether it is a translator or booster, the characteristics of the off-air signal is preserved as it is "translated" first to 10.7, then to the new oeprating frequency. Where an off-air signal is demodulated, and the composit signal fed to a transmitter, the non-linearities of the demodulator and modulator change the signal. With this scheme, the only limiting factor is the IF strip. Too narrow, and some information (e.g. SCA) can be lost.
Using an STL and conventional transmitter for a booster (as we do now, is much simpler to engineer. We send the signal on a Moselely 606 composite STL to the tower where our sister FM is located, and use an MX-15 and Scala FMV for the booster.
Crystal controlled receiver, with local oscillator 10.7 above or below receive frequency, mixer circuit, and the 10.7 signal then amplified, as in a typical FM receiver. However, instead of detecting the FM signal, the 10.7 IF signal is then coupled into a crystal controlled transmitter, where the IF signal is mixed again with the local oscillator to derive the new signal on a different carrier frequency, then amplfied.
With a booster the receive and transmit frequencies are the same. The problem, of course, then becomes the contamination of the receive signal by the much stronger transmit signal. Hence the receiver is placed in a sheltered location, then using the intermediate 10.7 mhz frequency, sent by the long cable to the booster's transmitting amplifier. There it is beat against another crystal oscillator to upconvert from 10.7 to the operating frequency. As noted, there is much less attenuation at 10.7 mhz then at the FM band; and it is also easy to build traps at both ends to keep FM band signals from being couple from one unit to the other. Usually the cable is buried to prevent the shield from coupling booster signal back into the receiver.
As can be seen, whether it is a translator or booster, the characteristics of the off-air signal is preserved as it is "translated" first to 10.7, then to the new oeprating frequency. Where an off-air signal is demodulated, and the composit signal fed to a transmitter, the non-linearities of the demodulator and modulator change the signal. With this scheme, the only limiting factor is the IF strip. Too narrow, and some information (e.g. SCA) can be lost.
Using an STL and conventional transmitter for a booster (as we do now, is much simpler to engineer. We send the signal on a Moselely 606 composite STL to the tower where our sister FM is located, and use an MX-15 and Scala FMV for the booster.
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