Re: [LPFM] STLs..
Licensed is a safer alternative as far as excluding yourself from as much interference as possible.
I'm going on 5 years ago when I used a mono 460MHz channel, It cost somewhere near $400-$500 to engineer a license then a small annual fee of about $100 or something like that. Things might have changed since though.
I'd also be interested to know what it costs for a 900MHz channel these days?
5-12KM's you won't need much power for a licensed STL. We used a 2W output in to low loss coax (about 20 metres LMR-400) then in to a 12~16dBi gain yagi antenna at both ends, used to get us about 20KM's - skimmed over a hill top to a non line of site receiver hence the need for 400MHz channel. 900MHz mono/stereo etc... would obviously be more picky about line of site.
You can modify analogue A/V senders but you're living with the chances of interference. Especially if the receive antenna is pointing over a township. The max you can output on analogue is 1W, keeping in mind most of the transmitters energy is spent on video output?
There's some digital audio senders around @ 2.4GHz that work well after being modified to have antenna out sockets with grid antennas. They do forward error correction, sound pretty transparent (uncompressed 16-bit 44,100Hz stereo, 20Hz-20KHz) and nothing else seems to work on the same channel when they are running. However it's still open to interference. They do let you use 4W since they are digitally modulated. I tried one over 3KM's non line of site in a 50,000 population town, didn't suffer any interference even with only about 10mW going in to a grid antenna. With a booster on the right cable to get 4W after the antenna they run extremely well.
Mosgiel on the back of Dunedin are using one, a DAS-100's digital sender, I forget the PCB board numbers now my other one is been tested elsewhere. That seems to still be working for them fine in the 2.4GHz band despite the receiver being able to change channel automatically if someone else sent it a powerful enough digital signal to it. There's newer one's that also use frequency hopping but I haven't personally tried them yet. However again, open to interference and require some blind setup work (no level metering etc...)
Depending on your spectrum use nearby I think there's a few other options. I think Ross still uses something down around 76MHz or something with an appropriate transmitter/receiver? It's a license free part of spectrum aswell, but again possible interference if it's not already in use to begin with.
Looking forward to others replies also on STL costs.
Gavin.
----- Original Message -----
Sent: Monday, July 13, 2009 8:38 PM
Subject: [LPFM] STLs..
Hi all,
Just wondering whether anyone could please give me the laymans low-down on STLs?
Supposing I'm looking to move my Tx to a higher location that's, say, 5-12k's away as the crow flies from my current studio location.
I've heard stuff about modifing a 2.4GHz AV sender by putting a high gain Rx & TX aerial (grid or otherwise) on the respective AV units. I understand these will work over short distances, but how about over longer distances?
Would it be better to buy a purpose built unit? If so, what would be an adequate power output, where would one buy one, and roughly how much would they cost?
I notice there are some 'free' frequencies in the 2.4GHz range, but would it also be better to get a licenced one? If so, what is the process and how much?
Thanks in advance,
Herb.
Send Email
