Filters & Gain?

[JackTV]

Hey All,
I have alot of intermod around my way (north of Baltimore & tv hill) i am using a
Radio shack FM trap and a Par 152 intermod filter.The antenna i am using is a
DPD 225-400mhz LPA.I am still getting some FM trash without the FM trap so
I still have it in line.The strange thing is when I inserted the Par 152 filter with
the FM trap it seems that my signal levels have really increased on both
VHF low (39.44 state police) and 800 mhz has increased also. I know this by
looking at my signal strength meters on my scanners.I am also using a
Stridesburg 4 port multicoupler.Does this make any sense?


Jack

 

[MB]

Hey All,
I have alot of intermod around my way (north of Baltimore & tv hill) i am using a
Radio shack FM trap and a Par 152 intermod filter.The antenna i am using is a
DPD 225-400mhz LPA.I am still getting some FM trash without the FM trap so
I still have it in line.The strange thing is when I inserted the Par 152 filter with
the FM trap it seems that my signal levels have really increased on both
VHF low (39.44 state police) and 800 mhz has increased also. I know this by
looking at my signal strength meters on my scanners.I am also using a
Stridesburg 4 port multicoupler.Does this make any sense?


Jack

Yes, this makes perfect sense. You must be getting some strong paging interference and overload in the 152-153Mhz pager frequency range. These strong signals are probably overloading and de-sensitizing the front end of you scanner, thus making it less sensitive on all frequencies. The Par 152 intermod filter is blocking these strong signals and allowing your scanner to receive as it should.

Try this test: Detatch the antenna from your scanner and run a search between the frequencies of 152Mhz and 154Mhz (with no antenna). See if your scanner stops on a strong paging frequency. If it does, this is more then likely what is happening.

You could also try just using the PAR 152 filter without the FM trap and see what happens.

By the way, what type antenna are you using? I am not familiar with the "DPD 225-400Mhz LPA". What brand and how much gain does it have?

 

[JackTV]

I am using a DPD Productions 225-400 mhz Log Periodic Antenna.Nice
antenna for the UHF Mil Air band. It also works else where in the VHF and UHF
range but it is tuned and built for the 225-400 mhz band. Check out his website
at DPD productions. I think it has around 8 Db of gain.

Jack

 

[MB]

I am using a DPD Productions 225-400 mhz Log Periodic Antenna.Nice
antenna for the UHF Mil Air band. It also works else where in the VHF and UHF
range but it is tuned and built for the 225-400 mhz band. Check out his website
at DPD productions. I think it has around 8 Db of gain.

Jack

Thanks for the info.

Did you try the search without the antenna?

Did my explaination make sense?

 

[JackTV]

Yeah as a matter a fact I did.Even with NO antenna and all of the filters
I was STILL getting intermod on 152.3.Not as much but still there.Neat trick.

Thanx,
Jack

 

[kb2vxa]

Jack, how do you get intrmod with no input to the scanner? That requires two or more very strong signals so it's highly unlikely. 152.300 is itself a pager frequency, likely you're hearing the offending pager alone.

It could be it's mixing with something on the FM band and causing intermod to show up on other frequencies so probably the pager trap (intermod filter) is all you need unless an FM station is mixing with something outside that band segment. BTW, that trap is made for mitigating herringbone on channel 6 video, not very effective and doesn't need to be because TV signals are so strong compared to what you're monitoring, it takes a lot to clobber TV from an adjacent band.

Hey, Jack >TV< should know that. (;->)

Bee boo, budda budda budda budda BRAAP! Let's make a dope deal! That's why the telephone company blocks incoming calls on pay phones. (;->)