Signal trap to block intermod

I'm getting strong intermod from a local pager service on 157.740 MHz. Is it possible to get a frequency-specific signal trap to block the interference?

On the brighter side of the problem, I have enjoyed reading the POCSAG text messages with a software package called PDW 3.10 - it's shocking how much personal information is released in these medical paging messages. One message I saw flash by gave the person's name, date of birth and the message "NOTE: HIV pos". You'd think this data would be encrypted but it isn't.

A Notch filter for the 157.740 frequency. But you may loose reception on nearby frequencies.

cmdrwill said:

A Notch filter for the 157.740 frequency. But you may loose reception on nearby frequencies.

Click to expand...

That's what I'm afraid of. There's a channel I really want to monitor on 158.805 and I'm afraid a notch filter may block out that frequency, too.

wbswetnam said:

You'd think this data would be encrypted but it isn't.

Click to expand...

Consumers often assume it's encrypted and safe, as you've found, it isn't. 157.740 is a common paging frequency used by hospitals, campuses and businesses. Since this is likely being run by a hospital or clinic, rather than a paging service, you'd think they'd be smart enough to caution their users from sending HIPAA protected data over the paging system. Would be interesting if you ever felt like figuring out who it is and notifying their HIPAA compliance officer that you can easily receive these text pages that include that sort of information.

Yes, you can get filters, but be aware they do a couple of things:
- they'll introduce some loss into your antenna system.
- they don't -just- block 157.740, depending on how much you want to spend, they'll block varying amounts of spectrum around that frequency.

Make sure you check out your entire antenna system for issues first. Make sure your connectors are tight and dry. Make sure they are properly waterproofed and any preamplifiers or splitters are of the proper type.
Unfortunately the broad front ends of scanners let a lot of this crap in.

The VHFSYM158HT notch filter at Par Electronics would do a great job of blocking your problem pager frequency. But as you're aware, it's going to crush your 158.805 signal too.

PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

They make great filters. I have several. They're well made and effective. Signal loss outside the notch range is almost negligible.

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We can design a filter such that loss on your desired frequency will be under 3dB. This would be a custom asymmetrical filter specifically for your issue.

Dale
for PAR Electronics, Inc.

Watch Ebay for a surplus 5" dia or larger Cellwave, Telewave, DB Products or similar VHF notch cavity. These will provide a fairly deep and narrow notch without bothering a signal 1MHz away very much. Expect to pay around $75 if they are priced right.
prcguy