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FM Radio Trouble

A

admcs13

Guest
Hello,

I am the station engineer for a non-profit educational 100watt radio station. We have been recentally having trouble with our signal.

Basically our singnal is barley reaching 1/2 mile when it normally receaches 15 miles.

The signal also "pulses" faintly every 1 second. So the higer value below is when there is a "pulse"

From the radio station, the line goes to the top floor and into an Orban Model 8100A, then into the qei 675 exciter.

--The exciter is reporting .3 (of a possible 1.0) DC milliampheres, set at IPA.

From there it feeds into the transmitter (qei 675-T150)

--Our transmitter reads:

"Collector voltage"
0-3 (DC VOLTS) (out of 100)

"Collector Current"
0-1 (DC AMPERES) (out of 10)

"RF Output"
0-1 (% POWER, RF OUTPUT) (out of 110)

(the needle for each value goes to the higher number on each "pulse" then back down to 0, repeating every 1 or 2 seconds.

And from there to our antenna.


Any ideas?
 
> Hello,
>
> I am the station engineer for a non-profit educational
> 100watt radio station. We have been recentally having
> trouble with our signal.
>
> Basically our singnal is barley reaching 1/2 mile when it
> normally receaches 15 miles.
>
> The signal also "pulses" faintly every 1 second. So the
> higer value below is when there is a "pulse"
>
> From the radio station, the line goes to the top floor and
> into an Orban Model 8100A, then into the qei 675 exciter.
>
> --The exciter is reporting .3 (of a possible 1.0) DC
> milliampheres, set at IPA.
>
> From there it feeds into the transmitter (qei 675-T150)
>
> --Our transmitter reads:
>
> "Collector voltage"
> 0-3 (DC VOLTS) (out of 100)
>
> "Collector Current"
> 0-1 (DC AMPERES) (out of 10)
>
> "RF Output"
> 0-1 (% POWER, RF OUTPUT) (out of 110)
>
> (the needle for each value goes to the higher number on each
> "pulse" then back down to 0, repeating every 1 or 2 seconds.
>
>
> And from there to our antenna.
>
>
> Any ideas?
>

Could be the PLL in the exciter is off. Have you tried shutting down the transmitter and bringing it back on-line? What's the VSWR at the output of the xmtr?
 
> --Our transmitter reads:
>
> "Collector voltage"
> 0-3 (DC VOLTS) (out of 100)
>
> "Collector Current"
> 0-1 (DC AMPERES) (out of 10)
>
> "RF Output"
> 0-1 (% POWER, RF OUTPUT) (out of 110)
>

Output power (to a close approximation) is collector voltage times collector current or 3 volts times 1 amp = 3 watts which agrees with RF power output. So it looks like the problem may be with the transmitter.

While it is possible that the power supply for the output stage (collector voltage) has gone, the fact that the signal is "pulsing" seems to indicate a problem with the output stage/feedline/antenna.

It looks like the transmitter is trying to output into what is close to a short and "crowbarring" causing the pulsing.

First check the SWR of the line to the antenna to make sure there is not an open or high SWR. Then use a VOM to determine if the trasnmitter is runnnig into a short.

If the antenna and feedline is good, then I would bypass the antenna and try to feed the exciter directly to the antenna. If that works, then I would suspect the transmitter is at fault.

Good luck!!!
John
 
> > Hello,
> >
> > I am the station engineer for a non-profit educational
> > 100watt radio station. We have been recentally having
> > trouble with our signal.
> >
> > Basically our singnal is barley reaching 1/2 mile when it
> > normally receaches 15 miles.
> >
> > The signal also "pulses" faintly every 1 second. So the
> > higer value below is when there is a "pulse"
> >
> > From the radio station, the line goes to the top floor and
>
> > into an Orban Model 8100A, then into the qei 675 exciter.
> >
> > --The exciter is reporting .3 (of a possible 1.0) DC
> > milliampheres, set at IPA.
> >
> > From there it feeds into the transmitter (qei 675-T150)
> >
> > --Our transmitter reads:
> >
> > "Collector voltage"
> > 0-3 (DC VOLTS) (out of 100)
> >
> > "Collector Current"
> > 0-1 (DC AMPERES) (out of 10)
> >
> > "RF Output"
> > 0-1 (% POWER, RF OUTPUT) (out of 110)
> >
> > (the needle for each value goes to the higher number on
> each
> > "pulse" then back down to 0, repeating every 1 or 2
> seconds.
> >
> >
> > And from there to our antenna.
> >
> >
> > Any ideas?
> >
>
> Could be the PLL in the exciter is off. Have you tried
> shutting down the transmitter and bringing it back on-line?
> What's the VSWR at the output of the xmtr?


>



I have tried shutting down and restarting both the exciter and the transmitter. I do not have any other readings from the devices.

If the antenna/feed to was the culprit, would all my power levels be this low?
What would be my best way to go about determining the problem? Would a dummy load help?


I appreciate all your help. We are a non-profit edu. station, so our resources are low. Thanks again.
 
> > > Hello,
> > >
> > > I am the station engineer for a non-profit educational
> > > 100watt radio station. We have been recentally having
> > > trouble with our signal.
> > >
> > > Basically our singnal is barley reaching 1/2 mile when
> it
> > > normally receaches 15 miles.
> > >
> > > The signal also "pulses" faintly every 1 second. So the
> > > higer value below is when there is a "pulse"
> > >
> > > From the radio station, the line goes to the top floor
> and
> >
> > > into an Orban Model 8100A, then into the qei 675
> exciter.
> > >
> > > --The exciter is reporting .3 (of a possible 1.0) DC
> > > milliampheres, set at IPA.
> > >
> > > From there it feeds into the transmitter (qei 675-T150)
> > >
> > > --Our transmitter reads:
> > >
> > > "Collector voltage"
> > > 0-3 (DC VOLTS) (out of 100)
> > >
> > > "Collector Current"
> > > 0-1 (DC AMPERES) (out of 10)
> > >
> > > "RF Output"
> > > 0-1 (% POWER, RF OUTPUT) (out of 110)
> > >
> > > (the needle for each value goes to the higher number on
> > each
> > > "pulse" then back down to 0, repeating every 1 or 2
> > seconds.
> > >
> > >
> > > And from there to our antenna.
> > >
> > >
> > > Any ideas?
> > >
> >
> > Could be the PLL in the exciter is off. Have you tried
> > shutting down the transmitter and bringing it back
> on-line?
> > What's the VSWR at the output of the xmtr?
>
>
> >
>
>
>
> I have tried shutting down and restarting both the exciter
> and the transmitter. I do not have any other readings from
> the devices.
>
> If the antenna/feed to was the culprit, would all my power
> levels be this low?
> What would be my best way to go about determining the
> problem? Would a dummy load help?
>
>
> I appreciate all your help. We are a non-profit edu.
> station, so our resources are low. Thanks again.
>

A bad antenna or feedline could send the transmitter into a VSWR protection mode where it scales back its power in order to protect itself.

You could see if it will fire up at normal power into a dummy load. If so, most likely it's an antenna or feedline problem.

If it has a "reflected power" reading, take a look at that.
 
If you have a minute we can speak on teh phone and look at it while you are on the phone. Email me at [email protected] and I will supply a toll free number. Probably after the weekend though.


> > > > Hello,
> > > >
> > > > I am the station engineer for a non-profit educational
>
> > > > 100watt radio station. We have been recentally having
> > > > trouble with our signal.
> > > >
> > > > Basically our singnal is barley reaching 1/2 mile when
>
> > it
> > > > normally receaches 15 miles.
> > > >
> > > > The signal also "pulses" faintly every 1 second. So
> the
> > > > higer value below is when there is a "pulse"
> > > >
> > > > From the radio station, the line goes to the top floor
>
> > and
> > >
> > > > into an Orban Model 8100A, then into the qei 675
> > exciter.
> > > >
> > > > --The exciter is reporting .3 (of a possible 1.0) DC
> > > > milliampheres, set at IPA.
> > > >
> > > > From there it feeds into the transmitter (qei
> 675-T150)
> > > >
> > > > --Our transmitter reads:
> > > >
> > > > "Collector voltage"
> > > > 0-3 (DC VOLTS) (out of 100)
> > > >
> > > > "Collector Current"
> > > > 0-1 (DC AMPERES) (out of 10)
> > > >
> > > > "RF Output"
> > > > 0-1 (% POWER, RF OUTPUT) (out of 110)
> > > >
> > > > (the needle for each value goes to the higher number
> on
> > > each
> > > > "pulse" then back down to 0, repeating every 1 or 2
> > > seconds.
> > > >
> > > >
> > > > And from there to our antenna.
> > > >
> > > >
> > > > Any ideas?
> > > >
> > >
> > > Could be the PLL in the exciter is off. Have you tried
> > > shutting down the transmitter and bringing it back
> > on-line?
> > > What's the VSWR at the output of the xmtr?
> >
> >
> > >
> >
> >
> >
> > I have tried shutting down and restarting both the exciter
>
> > and the transmitter. I do not have any other readings from
>
> > the devices.
> >
> > If the antenna/feed to was the culprit, would all my power
>
> > levels be this low?
> > What would be my best way to go about determining the
> > problem? Would a dummy load help?
> >
> >
> > I appreciate all your help. We are a non-profit edu.
> > station, so our resources are low. Thanks again.
> >
>
> A bad antenna or feedline could send the transmitter into a
> VSWR protection mode where it scales back its power in order
> to protect itself.
>
> You could see if it will fire up at normal power into a
> dummy load. If so, most likely it's an antenna or feedline
> problem.
>
> If it has a "reflected power" reading, take a look at that.
>
 
Not to overstate the obvious, but its always important to keep frequent logs on forms showing all of the meter readings, parameters, settings, etc., as well as work and modifications on your transmitting equipment so you can see when things begin to change (rapidly or even over time). That way you know when something is wrong or starts to go wrong and then you have a benchmark on how to know when you've restored things to the normal operating state.

> Hello,
>
> I am the station engineer for a non-profit educational
> 100watt radio station. We have been recentally having
> trouble with our signal.
>
> Basically our singnal is barley reaching 1/2 mile when it
> normally receaches 15 miles.
>
> The signal also "pulses" faintly every 1 second. So the
> higer value below is when there is a "pulse"
>
> From the radio station, the line goes to the top floor and
> into an Orban Model 8100A, then into the qei 675 exciter.
>
> --The exciter is reporting .3 (of a possible 1.0) DC
> milliampheres, set at IPA.
>
> From there it feeds into the transmitter (qei 675-T150)
>
> --Our transmitter reads:
>
> "Collector voltage"
> 0-3 (DC VOLTS) (out of 100)
>
> "Collector Current"
> 0-1 (DC AMPERES) (out of 10)
>
> "RF Output"
> 0-1 (% POWER, RF OUTPUT) (out of 110)
>
> (the needle for each value goes to the higher number on each
> "pulse" then back down to 0, repeating every 1 or 2 seconds.
>
>
> And from there to our antenna.
>
>
> Any ideas?
>
 
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