Band 1 track ?

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XXL
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Band 1 track ?

Post by XXL » Thu Jan 09, 2020 1:54 am

How hard/easy is it to trace a band 1 signal ? Iv heard because of the lower frequency, it’s a lot harder to track than the standard fm frequency’s. Band 1 tx in a loft somewhere ? Surly they won’t find that, only the general area.

Bton-FM
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Re: Band 1 track ?

Post by Bton-FM » Thu Jan 09, 2020 1:40 pm

I'm pretty sure its as easy to DF as band II.Most people with use it with an internet link to a midpoint then B1 to TX site.

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teckniqs
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Re: Band 1 track ?

Post by teckniqs » Thu Jan 09, 2020 3:09 pm

XXL wrote:
Thu Jan 09, 2020 1:54 am
How hard/easy is it to trace a band 1 signal ? Iv heard because of the lower frequency, it’s a lot harder to track than the standard fm frequency’s. Band 1 tx in a loft somewhere ? Surly they won’t find that, only the general area.
Sorry but we don't advise people how to track signals on this forum.

XXL
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Re: Band 1 track ?

Post by XXL » Thu Jan 09, 2020 4:53 pm

I’m not asking so I can go a steal peoples shit. I don’t do that. I’m weighing up the risk of band 1’ing off a particular place that I wouldn’t want to be raided.

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Re: Band 1 track ?

Post by Bton-FM » Thu Jan 09, 2020 5:41 pm

I’d say it’s a big risk

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teckniqs
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Re: Band 1 track ?

Post by teckniqs » Thu Jan 09, 2020 8:00 pm

I wouldn't recommend it

Albert H
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Re: Band 1 track ?

Post by Albert H » Sat Jan 11, 2020 1:57 am

Band I is really easy to track.

If you want to have a difficult signal to track, go up to band IV, near to the TV frequencies. You can use cheap multi-element TV Yagis at each end (remembering to match your gear into 75Ω and use 75Ω TV downlead for the connections. My old link receivers used TV tuner heads for the front end since there's no point in reinventing the wheel - especially when you can get a fully built and aligned high sensitivity tuner module for about £4. The IF out of the ones I used was 35 MHz - so mixing with a crystal oscillator to feed an ordinary 10.7 MHz IF strip made the receiver (effectively) a dual-conversion type.

Using one of those at the receive end, and a 32 MHz PLL circuit multiplied up to the output frequency for the link transmitter, with a pair of grounded-base 2N3866s for the "PA" (giving about 1 Watt), and a pair of 24-element TV aerials, I got a clean stereo link over about 8½ miles!

Another big advantage is that a TV aerial doesn't look out of place on any rooftop!
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Re: Band 1 track ?

Post by XXL » Sat Jan 11, 2020 6:24 am

I would use band 4 but I cannot find a schematic, and I’m tryna work out how to demodulate a tv tuner.

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Re: Band 1 track ?

Post by Bton-FM » Sat Jan 11, 2020 10:52 am

What you need XXL is a Mixer of some sort (dual gate mosfet I think works well?), An oscillator (crystal is good because it is stable and and negates the use of a PLL) and a 10.7 mhz IF strip.The crystal would either be 35mhz-10.7mhz=24.3mhz or 35mhz+10.7mhz=45.7mhz.I haven't ever done this but that's what I gather from reading old posts.

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Re: Band 1 track ?

Post by Albert H » Sun Jan 12, 2020 1:24 am

I used to use a 45.7MHz crystal oscillator (actually 15.23MHz tripled). The IF strip I used to use was one from Ambit (later called "Cirkit"), which was easily modified for PLL demodulation. I bought hundreds of those boards! The front end module was (usually) a Philips UV816, and this was tuned using a PIC talking I²C. The PIC was in a little box on the PCB, to prevent harmonics of its clock desensitising the receiver. The main receiver PCB was about 15 X 8 cm and had its corners cut off so it would fit easily into a standard diecast aluminium box. The aerial input was a 75Ω BNC, and SMA, an "F"-type or even a Belling-Lee (TV type). The demodulated signal came out of a phono socket, and power went through a 2.5mm power connector. There was also an option for remote switching (using sub-audio tone). The whole receiver cost around £30 to make, and out-performed anything else.

The transmitter was a dual-gate FET oscillator, phase-locked at around 32 MHz (using the three- chip CMOS trick), then a multiplier strip with copious filtering to get rid of spurious responses. There were two versions - 1 Watt and 5 Watts. The 1 Watt version used a pair of 2N3866s in grounded-base mode for the final, and the 5 Watt version used a BLY83. There were a few versions of the board built - some even with incorporated stereo coder and limiter - and these were all matched into 75Ω to allow the use of TV Yagis.

In later times, I used the TSA5511 PLL chip, and generated the Band IV carrier directly at frequency. I found a Mitsubishi power module for a few pounds that took all the grief out of building PAs at UHF, The rigs became very simple and quick to build. The power modules were available at 7 Watts and 23 Watts - I down-rated them to 5 Watts and 20 Watts - and I never managed to blow one up!
"Why is my rig humming?"
"Because it doesn't know the words!"
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