Ok, this might sound like a bit of a stupid question, but what exactly are pager transmissions?
I’m talking about the transmissions that sound lowish data rate in bursts of a few seconds. People are always referring to them as pager signals. Is that right? I haven’t seen anyone using a pager for decades. Is this a legacy system from last century?
Even my Yaesu VX7, never mind the Baofeng, gets pretty hammered.by a near-by transmission, as yesterday on Cleeve Hill. So I’m just curious to know what’s behind the great density of these sources of interference.
Not having a handy Site Master or a little R&S job to stick in the back pack where in the spectrum is the hot spot for these, in case I consider any filter construction?
RO pagers and bidrectional pagers are still used. RO Pagers are used where mobile phones are a big no-no. The transmissions are on around 135MHz and 153MHz off the top of my head. So they blanket our 2m band and if you have a 2m handy with wide RX you will probably find it gets badly overloaded when you fit a better antenna and operated near these things. Some are more resilient. Or you can use an FT290 and have no problems.
Yes you can make a filter that has a low insertion loss on TX and RX, there’s much discussion in the archives.
I live about 250 yards from a comms tower, my Yaesu FT-8800 gets hammered with pager interference and some frequencies on 2M are unusable. Yet my 817 doesn’t suffer at all. Very annoying at times.
I wonder how expensive it is to keep the network running. Presumably the user-base will have shrunk somewhat.
Right - I’ve found a few of the threads off the old reflector. A helical filter is I suppose the obvious candidate. I’ve not built one of those before - could be fun.However, I wasn’t able to find a full description of anybody’s SOTA-inspired 2-m helical yet.
But then again if I can find some .141 semi rigid I could be tempted to try a stub filter as per May 2000 QST article.
Yes FT817ND on the Wrekin by the trig point receives fine. My VX-7 handheld with its wideband receive is rendered deaf by the pager transmissions from the commercial mast on the summit.
happy New Year / Blwyddyn Newydd Dda
David M0YDH
Just to interject something that probably sounds silly, but back in the 60’s a friend of mine made a simple cavity filter based on a cocoa tin. By modern standards it was a clunking great thing but it worked!
I seem to remember that there is or was a helical filter available off the shelf that would tune down to 130 MHz, so it might be worth doing a Google search for it.
Thanks Richard - nice little program. I must try some of the other utilties on that site - several look interesting.
What was your arrangement with the penny / 5p tuning element? It wasn’t clear to me how the helix-side of the C was constructed.
Years ago I made a cavity filter for 70cm (was living next to Jodrell Bank at the time, so there was some pressure to stay in band). It would make up a large fraction of my SOTA pack if I scaled it to 2m! I get through lots of cocoa but the tins are just metalized cardboard…
Well, it joins a long list of projects it would be nice to try; probably I should look out for something ready-made - or just try the 817 as the consensus seems to be that it’s better.
I did once try to use a coax stub, but didn’t find them to be very good. As Andy suggest the Q and notch depth are not really good enough.
My FT817 is one of the best radio’s I’ve used in close proximity to such problem transmissions, even some other radio’s that don’t have wide-band capabilities are sadly lacking in filters to eliminate such strong signals. I seem to recall that the TR-751 is quite poor and suffers even when 1/2 mile or more from some sites.
Rob,
I admit I’ve not used my current TR-751 (which I’ve had just a few months) within close range of any summit with such transmissions, but I vaguely recall having some issues with a previous radio (maybe it’s old age and it wasn’t the TR-751 at all).
Just a bit about Radio Paging. I’d suggest that these are not going away anytime soon. Lots of safety related organisations use them because they don’t rely on the mobile phone networks. Page One are pushing a three way device at the moment that uses VHF and UHF, plus SMS through a mobile operator. They are not cheap… but some organisations need very high confidence of message delivery
