This issue began appearing in the 1980s, when the Japanese manufacturers began expanding the frequency bandwidth of the mobile radio receivers. Savvy operators embraced the Kenwood TM-2530, 2550, and 2570 mobiles as they were relatively immune to intermodulation, cross mod, and blocking from the high-powered paging transmitters.
I remember my business Motorola HT from the 1980's. It rejected all but the UHF repeater while I was standing on the skyscraper rooftop where the FM transmit antennas and a TV antenna were. A regular radio would surely have de-sensed or overloaded. For the noobs, keep this in mind when you purchase a radio that has a very wide bandwidth. In order to hear all these bands, many manufacturers cut corners in the filters, so you'll probably need to add an external filter if you're in a moderate RF location. 73
My Tempo S1 (AOR AR240) handy 1978 covered 140 to 150MHz with little blocking, it was one of the first handys with a varicap tuned front end. Icom copied it with the IC2A, but they used a wide fixed tuned front end.
When a lot of the broadband 2M rigs came out in the 90's they suffered badly from pager network interference, yet the older IC22S, with its helical resonators in the front end was rarely bothered by them.
Nooelect makes a bunch of nice bandpass filters. I have all the weather satellites on one. Its catching a few weather satellites images now and I have a FM radio bandpass all inline and one with a bias T if you want. They rub 20-30 USD each and work really well.
Howdy Hayden. theres a company here called Morgan Systems that make excellent filters for 80m, 40m, 20m, 10m,. etc. they are high quality so tend to be a little pricey. I bought one of their AM Broadcast Filters because of interference from a local 1KW AM Station that was making a bunch of noise on 40m and 20m. works beautifully.
Combline filter? Ahhhh the "black arts" of VHF. What is the power capacity through it (EME so it must be high?). Thanks for the vid informative and educational. 73 de VK2AOE
Great video, you've also reminded me that I need to zero my setup and cabling on my hp more often 😂. Shame its not as sharp on the high end with its roll off... I get some bad pager tx intetmod here. Hopefully this filter doesn't suffer the problems with vibration flat pack duplexors do and go out of tune. To conclude, the real test will be PIM on the repeater. 👍 Cheers VK2VRK
Thanks mate. Yeah obviously with it needing to cover the whole of 2m, pagers at 148 MHz aren't as attentuated... a separate notch is probably better for that. Honestly, without opening up the filter - I don't think there will be that much vibration issues. Just waiting for the snow to melt before getting it up on the mountain!
Yeah I'd be interested to see what a sweep of the spectrum looks like once you go onsite on a analyser... A notch, yes well too much filtration will obviously have too much loss.. I'll be watching this one with keen interest.
Microprocessor noise. When this started in the 1990s we called the myriad carriers and noises "space invaders" after the video game, and because they were invading our space.
In Vienna we have a TV propaganda broadcast transmitter at about 498MHz causing problems to all those cheap direct sampling receiver radios. You can fix that with a bandpass filter.. or you buy a radio with a superheterodyne receiver. 😁
So when do you try it out on your repeater ? I had a similar issue with high power TV transmitters at the same site and found that added filtering did not help because the problem was low level wideband noise from the TV tx. No cure possible except at source.
Yep, band pass/ band reject. I had to buy a FM filter for my scanner because of interference from 96.9. If you want to see something amazing take a look at how much harmonic attenuation a simple antenna tuner gives.
