Band 1 Link advice

[OldskoolPirate]

Can someone advise me on band 1 links and how to setup/use one.

So you buy a rig from a builder with a band 1 rx inside. How does the builder know what frequency your tx is on. Or on the other hand, how do you know that another pirate or legal service isn't using the frequency your box is tuned to and when you switch on it starts playing their link????

Iv only used microwave until now but the satcans are getting too hard to source now days.

Thanks

[Analyser]

You either need to tell the builder your link frequency if you have a link box already, or give it to him and he'll find out for you.

If your builder is local to you then they normally have a pretty good idea of who is using which B1 frequency in that area. If that's not the case and you're unlucky enough to land on someone else's B1 frequency then it all needs to go back for a retune, but not really a problem.

[Roobru]

Sorry for jumping on your post, but a quick question. Why do pirates use band one instead of three? Or are those frequencies too congested or is there quality issues?

[teckniqs]

It's now mainly used by PBR, PMR radio now like TAXI firms etc so as you say too congested, where as band one is completely clear in the UK from around 53MHz to approx 68MHz.
You will find the RSL and community station using band I STL around 48-50 and 52-53MHz.

[Albert H]

Band I has vast open areas, so it's easy to find a quiet gap to use. It also penetrates buildings well, and isn't too directional. The downside is that the wavelength is around 5m, so a dipole is 2.5m long and very obvious up a block or on a rooftop.

I prefer to use frequencies up in Band IV, around 550 - 650MHz, which allows the use of TV Yagis at each end (which never look out of place). The receivers are easy - you can use TV receiver modules (much easier to find these days than satcans!) and there are simple PLL circuits for these frequencies.

The power transistors for the transmit end can be cheap 2N3866 (I frequently use a parallel pair for about 1.5 Watts), and the VCO can come from another TV tuner-head. The TX line-up is a TV tuner-head with a prescaler (÷64) built-in, feeding a pair of BFR96s, into a pair of 2N3866s. The receiver is another tuner-head, which has an IF output at ~35MHz, mixed with a crystal in an NE512, into a standard 10.7MHz IF strip.

One thing to note - the TSA5511 PLL IC (often found in TV tuner modules) works at any Band IV or V frequency (it was designed for TV receivers).

I even use TV coax and Belling-Lee (TV-type) connectors for the aerials, and I've managed fully noise-quietening stereo links over ~40km with about 1.5 Watts into a 24-element TV yagi. Remember that the TV stuff needs to match to 75Ω instead of the usual 50Ω.

There are big gaps between TV channels (the "guard bands") and it's easy to find a quiet spot. I put one link in the vestigial sideband of BBC 2 (back in the analogue TV days), which made it virtually impossible to track - you'd end up at Crystal Palace!

The "engineers" around today are lazy and not the most competent. They don't think about the impracticality of a 2.5m dipole and how obvious it is now that most Band I aerials have gone from rooftops. They just have a "recipe" for a crude Band I receiver (anything else is too complicated) and they continue to sell this rubbish to stations.

Station operators: you can find out how competent your "engineer" is by asking for a Band IV link system. 90% of them won't have the first clue (even with the hints I gave above!)

[thewisepranker]

I'd steer clear of those horrible Belling-Lee connectors. An F connector is much, much better and is usually cheaper. But not one of those crappy screw-on ones.

[shuffy]

Crikey, I hadn't done a band IV link in years until one I did on a midpoint a couple of years back. I used to use a very similar scheme to the one Albert described for the receiver, but the TX's were cobbled together from whatever came to hand; old PMR gear, pocketphones (actually we used a PF1 sawn in half for a receiver once as the front ends were legendary), 70cm ham gear if it would re-tune up to 470MHz and even comepletely bespoke transmitters. You didn't need to frequency synthesise the rigs, a simple AFC loop would do.

The vestigial sideband trick was also well used. These days if I was using an analogue UHF link, I'd probably use highly directional antennas and try to hide my link in a distant digital mux in the null of the receiver's beam.

Back in the day, I always used BNC connectors for the antennas on UHF, unless using a TV front end in the receiver. For the link I did recently (around 450MHz), I was using SMA which whilst potentially unorthodox at those frequencies was fine.

Band I for a link never struck me as a sensible idea. Antennas too big and cumbersome, and too easy to trace. Plus, it always struck me that it would be harder on Band I to create filter circuits with high enough Q to stop your main TX overloading your front end. Having said that though, I've seen plenty of modest band I gear that gets away with it and performs well.