Input need for Off-Air signal distribution

[sattec]

hey mike, I have a garden style apartment complex wanting me to put the off air tv signal only, into the trunk. How much trouble is it to send the off air through a 1300 ft trunk with 6-8 buildings on it? The highest analog channel is 60. FOX is on analog 2 and digital 48.3 (uhf 49), theres about 18 digitals in the area, it takes two antennas to get everything just right...I want to know about the trunkline distribtution, and the processing in the H/E before I send out the signal....I know you've said it all a 1000 times but could you go through it again, there's is 101 overlay in place also. So it's off air and an st-101 on the trunk....

[AntAltMike]

Is the L-band already traveling through this trunk? What size cable is it? That would be an awfully long trunk for L-band.

[sattec]

yes, - I use pal -5's to keep it going...really about six buildings is as far as I can go before the s/n is bad....I used al-16 boxes from sonora....it's flex feeder from pace and hardline 540...

[AntAltMike]

So apparently, you can withstand the loss at 2GHz from line extender to line extender, so you need line extenders with the bandwidth to handle the off-air as well as the L-band.

I haven't done much looking into available hardware with that much bandwidth that can be develop the power levels you are needing. Generally, a fully loaded cable TV system would need amplifiers that develop an output level of about 44 dBmV with a 100+ channel load, but SMATV systems with lighter channel loads are sometimes engineered with the assumption that at each amplification point, a Blonder Tongue BIDA or its inline equivalent will boost the trunkline back up to close to 50dBmV.

I'm not familiar with the Sonora distribution boxes you are using, so the way I'm picturing this is, you leave a PAL -5, go some distance, and tap off at, say -16dB, then at the next branch, you tap off -12, and then -8dB, and then maybe you have a two way splitter where half the signal goes into your distribution box and the other half becomes the input to your next line extender.

Sonora Design has some strong AU9 wideband trunkline amps that pass 250- 2,150 MHz, so if you were building a new system, you could use those if your analog channels began in the upper 20s, but for an existing system, that would mean moving over two dozen channels to higher channel numbers.

I haven't yet swept any of their 250-2,150 MHz amps to see if they pass and amplify signals below 250 MHz or if they have a filtered rolloff at that point. I have a dozen in a box for job I haven't yet gotten around to installing, so I eventually will be able to check them.

I'm sure that Spaun makes inline, splitband amplifiers that will handle both cable and L-band, but I have been avoiding using them in large buildings because their most powerful products were about 10dB weaker than Sonora's. Last I checked, Spaun rated their amps with a one transponder analog load referenced to an intermodulation benchmark of -35dBc, and published the rating in decibel microvolts, to boot, so it took a little arithmetic to figure out just how high you could drive them with your likely channel load.

You subtract 108.75 dB to convert from decibel micovolts to decibel milliwatts, then you subtract 3dB for each doubling of the channel/transponder load, so if you have 32 equal strength transponders and cable channels, for a total of 64, then you derate the output by either another 15 dB or 18 dB, depending on if it is internally a split band amplifier or a single wideband amplifier, and then you have to drop it another 2.5 dB to reference it to -40dBc intermodulation distortion, because that is the Holy Grail for DBS satellite, and then you further derate it by, I think, another 6 dB for each time you double the number of amplifiers in your cascade.

So if a Spaun product says that it can develop 116 dB microvolts with a one transponder analog load while developing -35dBc of intermodulation distortion, and if you are feeding it 32 transponders and configuring it in a four amp cascade, then it can develop 116 minus 108.75 for the simple conversion factor, minus 15 dB to adjust for the 32 transponder load, minus 8.5dB to get each amp developing just -52dBc of intermod for a system intermod of -40dBc, then that means that each amp can only output -16.25 dBm (note I just did all this arithmetic in my head at 3:15 AM eastern time, so God only knows how much sense this will make in the morning!)

Now, assuming that the terrestrial/cable analog amplifier in such a split band amp is similarly robust (and I admittedly have never really analyzed them), then you are looking at analog output signal output levels of only about 35dBmV or weaker, which would ordinariy be inadequate to meet the distribution needs of most MATV systems, but with these 16 port Sonora distribution boxes, it may be more than adequate to meet your needs.

Did someone actually engineer the L-band distribution amplification cascade you are using now, or did you just "wing it"? Sonora will engineer them at no charge if you give them the parameters (coax lengths and gauge, number of ports, available line voltage locations).

[sattec]

holland electronics did the design, the design is good, it works perfect. thanks for the input mike, I'm gonna study what you wrote...there's a lot of good info in your last post, I'm glad I didn't pm you with my question, you just helped a lot of folks.