165.8875 and 454.250mhz voice pagers ripping my VHF UHF apart

[adsbgreenock]

Hi Guys,

Hope you're all well.

I have a uniden sds200e and have it hooked upto 2 x diamond x510n about 40ft apart, same height and same run of Messi Paoloni ultraflex 7 coax etc etc.

I am on top of a hill next to the River and right across from me is a damn hospital which has a Voice switchboard pager thingy with the whole tune of beeeeeeee--eeeeeeerrrrrppp bweeeeee-eeeeeeerrrrp grrrrrrrrrrrrrrrrrr thing going on and it's starting to do my melon in tbh😔

I have tried the antennas single and also every which way and nothing is helping.
They other day I decided to switch on the rspduo just to get an idea of what was happening on the spectrum and i couldn't believe it.
Each time a "Bing Bong! Testing switchboard team huddle contact yadda yadda yadda This is a test" was relayed, all my 453mhz and 456mhz DMR spikes were drowned with a big wave of splatter on each side of the 454.250mhz frequency.

Try VHF? Its even worse down there, not happy with UHF they wanted to holler all around there as well🙄I'm at a loss.

Is there anyway I can Kind of mute them a little to allow my other little signals a chance to demodulate.

Any help, as always is appreciated

 

[iMONITOR]

Have you tried setting the various filters in the SDS200 settings? Start there. You might need an external filter, maybe two. Contact PAR Electronics and discuss the problem with them. They should be able to help you.

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

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

www.parelectronics.com

 

[G7RUX]

This is a common issue and it is often caused by intermodulation in the receiver.

The first thing to do is to look at the levels of the interfering noise and pop a 10 dB attenuator in the antenna feeder. If the noise products drop by much more than 10 dB then it's definitely intermodulation that's causing the problem. If not then it is likely a problem with the transmitters (or intermod on the hospital rooftop but that's not common.)

If it is intermod in your receiver then the only way to deal with it is to reduce the incoming level of the pager signals. This can be done by attenuating everything which is simple but unsatisfactory, or by attenuating just the problematic signals with filters.

Commercial filters can be bought to block (bandstop) the problematic frequencies, or to high-pass/low-pass as appropriate if that works for the frequencies you want to receive.

It is also quite possible to make your own stub filters which aren't complicated but need a bit of tweaking to get them to work well.

If you want to try making your own then here are a few good links...

I like this method the best: New Page 1

Coaxial Stub Filters from G4SWX

Coaxial Stub Notch Filter Designer

Coaxial Stub Notch Filter Designer

www.changpuak.ch

Have a go and see what happens, it's cheap and fairly easy to make simple stubs and can be quite effective. The simplest type just use a t-piece in the feeder and an open length of coax; trim it slowly to bring the notch onto the pager frequency you want to reduce.

As an aside, why do you have two X510 antennas and how are they connected and physically arranged?

 

[adsbgreenock]

@iMONITOR @G7RUX

Thanks for the response,

I have tried an attenuator, this was a satellite type one, although it dropped the interference a little but not too much that I noticed any improvement. First i had tried it in line with an amp to increase the weak DMR signals. However due to the problem with the interference I was only magnifying things.

So, for a period I left the Ftype connector attenuator in place and like I said, I didn't notice anything by way of considerable changes.

My antennas are actually diamond x50n and I favoured these over the discone which was okay for like airband stuff.

I have the two so I can switch between which sometimes helps a little.

I'll have a look at the links and check them out.

Thanks

 

[W9WSS]

PAR filters took care of both of the issues I had with two paging companies over 15 years ago. One was on 158.10 MHz, while the other was somewhere in the 454 MHz region.

When the paging system shut down, I didn't need the PAR filters anymore.

 

[vagrant]

I use filters made by Dale Parr and they work well to block paging signals. The filter will not block it 100% of course, but it works very well. With one nearby multi-site VHF paging system I use two filters inline to block the same frequency as the RFI is really bad. Find out the exact offending frequency and perhaps confirm it with an FCC search. Contact Dale and let him know the freq. He will tune the filter for it and then he sets the screw.

Last I checked they were around $80 and it may take a week or two as he is busy with orders.

 

[adsbgreenock]

Hi Sir,
Thats a decent price and well worth paying
Usually any time I see a site with no prices I tense up for the kindey blow 😏 bearing in mind I'm also in the UK?
Do you know if he ships out of US

I'll drop him a mail and see.

Cheers and beers

Regards

 

[vagrant]

I was not paying attention and presumed you were in the U.S.A. regarding the FCC search. As to shipping, unknown, but if he does not reply in a day or so, email him again. He gets busy with bulk Gov. jobs so you may have to reach out twice.

I think I have around 10 different filters he makes.

 

[paulears]

A notch filter will work pretty well. The coax ¼ wave ones are nice and simple but quite wide band so you will lose channels around the cut frequency. I suppose the real issue is simply proximity. Years back I lived next to a fire station, and their pagers were 50 ft away from me and nothing worked.

 

[G7RUX]

A notch filter will work pretty well. The coax ¼ wave ones are nice and simple but quite wide band so you will lose channels around the cut frequency. I suppose the real issue is simply proximity. Years back I lived next to a fire station, and their pagers were 50 ft away from me and nothing worked.

If you cut them for harmonics then you can make fairly tight notch filters; see the first of the links I posted. It's complicated to understand the interplay of the odd and even harmonics but it makes sense once you see it working.

 

[paulears]

Totally agree for tighter bands, but for a user who wants to hear what there is on the spectrum, wider filtering is pretty destructive. For me, a nasty pager on 155, messes up the weak coastguard on 156, but so does a wider band filter! That said a vhf 4 or 6 cavity filter at best knocks out a couple of MHz when used in notch mode.

 

[G7RUX]

Absolutely so. However, intermodulation of this sort is typically 3rd order, so reducing the unwanted by say 6 dB will result in the troublesome intermodulation products reducing by 18 dB. A moderate reduction in the interferer shouldn’t massively affect nearby other wanted signals unless they are very weak.
Unfortunately pager interference is a very difficult issue to deal with without moving the receiving site further away so any measure is likely to be somewhat of a compromise.

 

[Ubbe]

The RSPDuo isn't doing much better than the receiver chip in the SDS200e.
Spec says at the lowest gain setting you have a noise level of 37dB(!) and IP3 of 27dBm
At max gain you get a noise level of 3dB and IP3 of -24dBm

If I remember correctly the standard notch filter that PAR quoted me was $150 incl shipping and then add VAT and customs fee.

Coax stub filter can be used as a test. I use a twist on F connector and then unscrew the coax from the connector a turn or two to fine tune it. As you can watch the spectrum you can easily see when you reach the max notch while cutting the coax, which will be some 20dB attenuation that might not be enough if you saw no reduction to the interfered signal in comparison to your monitored signal. You can try two stubs just to check that it will actually help with a notch filter and you can even include that 10dB attenuator.

Bandstop Filter versus Coaxial Stub

I have seen this theme before and wanted to post an image of one of our asymmetrical notch filters and a 1/4 lambda open stub comprised of RG-8X. This filter is designed to recover more quickly on the high frequency side of the notch. The assymetry can be reversed so as to recover more...

forums.radioreference.com

/Ubbe

 

[G7RUX]

The RSPDuo isn't doing much better than the receiver chip in the SDS200e.
Spec says at the lowest gain setting you have a noise level of 37dB(!) and IP3 of 27dBm
At max gain you get a noise level of 3dB and IP3 of -24dBm

If I remember correctly the standard notch filter that PAR quoted me was $150 incl shipping and then add VAT and customs fee.

Coax stub filter can be used as a test. I use a twist on F connector and then unscrew the coax from the connector a turn or two to fine tune it. As you can watch the spectrum you can easily see when you reach the max notch while cutting the coax, which will be some 20dB attenuation that might not be enough if you saw no reduction to the interfered signal in comparison to your monitored signal. You can try two stubs just to check that it will actually help with a notch filter and you can even include that 10dB attenuator.

Bandstop Filter versus Coaxial Stub

I have seen this theme before and wanted to post an image of one of our asymmetrical notch filters and a 1/4 lambda open stub comprised of RG-8X. This filter is designed to recover more quickly on the high frequency side of the notch. The assymetry can be reversed so as to recover more...

forums.radioreference.com

/Ubbe

Being third order effects, intermodulation products should reduce by three times the reduction in interferer level.

 

[adsbgreenock]

The RSPDuo isn't doing much better than the receiver chip in the SDS200e.
Spec says at the lowest gain setting you have a noise level of 37dB(!) and IP3 of 27dBm
At max gain you get a noise level of 3dB and IP3 of -24dBm

If I remember correctly the standard notch filter that PAR quoted me was $150 incl shipping and then add VAT and customs fee.

Coax stub filter can be used as a test. I use a twist on F connector and then unscrew the coax from the connector a turn or two to fine tune it. As you can watch the spectrum you can easily see when you reach the max notch while cutting the coax, which will be some 20dB attenuation that might not be enough if you saw no reduction to the interfered signal in comparison to your monitored signal. You can try two stubs just to check that it will actually help with a notch filter and you can even include that 10dB attenuator.

Bandstop Filter versus Coaxial Stub

I have seen this theme before and wanted to post an image of one of our asymmetrical notch filters and a 1/4 lambda open stub comprised of RG-8X. This filter is designed to recover more quickly on the high frequency side of the notch. The assymetry can be reversed so as to recover more...

forums.radioreference.com

/Ubbe

Hi Ubbe,

After some reading and fiddling around with the coax stub attenuator I managed to build and fit one.
Result is astonishing. It's all but cured my problem. My scanner is receiving other DMR signals +/-1mhz below the problem pagers.

Thanks everyone who chimed in.

Much appreciated


Regards

 

[G7RUX]

Hi Ubbe,

After some reading and fiddling around with the coax stub attenuator I managed to build and fit one.
Result is astonishing. It's all but cured my problem. My scanner is receiving other DMR signals +/-1mhz below the problem pagers.

Thanks everyone who chimed in.

Much appreciated


Regards

Did you go down the route suggested by the link I posted? I can give a spreadsheet that allows one to calculate lengths needed and to also see what they do on nearby frequencies. I should really put my pair of filters on the network analyser to do a write up.

 

[adsbgreenock]

Did you go down the route suggested by the link I posted? I can give a spreadsheet that allows one to calculate lengths needed and to also see what they do on nearby frequencies. I should really put my pair of filters on the network analyser to do a write up.

Yes apologies. it was yourself and Ubbe suggestion and advice . Thanks for sharing the link with me.

Excellent.

Regards

 

[G7RUX]

Yes apologies. it was yourself and Ubbe suggestion and advice . Thanks for sharing the link with me.

Excellent.

Regards

No problem, you are most welcome. They come out pretty tight too if you choose a nice high multiple.

 

[Ubbe]

My scanner is receiving other DMR signals +/-1mhz below the problem pagers.

Did you cut the stub to its fundamental frequency and not its harmonics? My analyzer picture show that the fundamental frequency are the narrowest and deepest one, if you look at the 6,95dB attenuation bandwidth.

Just keep an eye on the harmonics so that they doesn't do too much damage to another frequency you are monitoring.

/Ubbe