[FADCA] Anticipated Signal Levels- 9.6KB

[John H. Green]

HI
I think you answered your question when you indicated that 1uv was 
required for a low bit error rate. Anyhow, I ran some path loss/fade 
margin examples to see how it looks. The 1 uv really puts a damper on 
the fade margin as shown below. Changing the rx sensitivity to .8uv and 
leaving everything else the same moves the fade margin out to 5,7 db - a 
little safer - using .5 gives a 9.8 db fade margin. Doug says you need 
30 db for a 99% reliable path, but I think with a 1 uv rx value you have 
a lot of margin built in. The error rate might go up but things will 
still work.
Changing any of the parameters like height, antenna gain, power will 
help, doubling the tx power adds 3 db fade margin.

Thus, if you specify the rx sensitivity for the desired bit error rate 
and the desired fade margin you can play with the other values to 
achieve this.. Since a lot of things are determined by chance (available 
tower space) rather than design in our network we have less to play with 
than most folks.. :-(

By the way Bud, did you ever try the setup for the pk9612?? :-)
73 John


Frequency: 446···· MHz Terrain Type: 2 (1-5)
───────────────────────────────────────────────────────────
Transmitter Receiver
TX Power: 50·· W RX Sensitivity: 1··· uv
Antenna Height: 100·· ft Antenna Height: 100·· ft
Antenna Gain: 6··· dB Antenna Gain: 6··· dB
Antenna VSWR: 1.2· (x:1) RX Line Loss: 1.4· dB
TX Line Loss: 1.4· dB
───────────────────────────────────────────────────────────
Call Sign: N0IA··· Customer: pbpg················

ERP = 143 W (51.6 dBm) Radio Horizon = 28.3 mi
Comm. Quality Beyond 28.3 mi is Path Critical
Estimated Usable Range = 33.9 mi

For distance between TX and RX = 30 mi
Free-Space Path Attenuation is 119.1 dB
Signal Fade Margin is approx. 3.7 dB




bud thompson wrote:

> Who can comment with specific experience?
>
> All else being equal - Where there is a dedicated backbone w/o any 
> QRM....
>
> Question: What RF signal level can be expected at the receiver input?
>
> Put two UHF 9.6kb backbone stations 160 miles apart in Florida and 
> there is no signal.
> Put two UHF 9.6kb backbone stations 10 miles apart and it shouldn't 
> take much power to make them work.
>
> In our Reality Packet network in Florida, backbone links will be 30-55 
> mile paths.
>
> What is a reasonable minimal uv of RX signal we can expect to 
> accommodate?
>
> This is not a WEAK SIGNAL service.. we want 90%+ efficiency 24/7... 
> this is not satellite or meteor scatter packet. If it takes 100w and a 
> 13el beam that is okay.
>
> Our subjective tests today (Mitreks on each end) indicate that we can 
> have very good transfers at 1.0uv. Lower than that the throughput 
> suffers.
>
> bud N0IA
>
>
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