[FADCA] Anticipated Signal Levels- 9.6KB

[bud thompson]

----- Original Message ----- 
From: "John H. Green" <wb4moz at adelphia.net>
To: "Florida Amateur Digital Communication Association" 
<fadca at mailman.qth.net>
Sent: Monday, January 17, 2005 23:03
Subject: Re: [FADCA] Anticipated Signal Levels- 9.6KB


> 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
>

<snip>

John..

Thanks for the notes... I had to work a tad at digesting all that - and we 
had a workshop/demo in Sumter County last night..

The useable range of  33.9m with what may be a 'typical' set up isn't all 
that bad.  Affecting that would be most of my three sites are 140 ft minimal 
agl which should add some fade margin.  I don't believe any of our UHF 
receivers have higher than 1uv sensitivity and some are even better.  None 
have those nifty UHF preamps so that is another thing we might consider if 
the margin is to marginal.  Where we have more than 40 miles we plan on 
using 10-12 dbi gain antennas, almost doubling the power to gain that 
additional 3db you mentioned.

On the other side, most of the sites here have more feed line losses.

I sent Chuck specific data on all my UHF links and he will be running his 
program as time permits.

I have played with the KPC9612 (KAM dual port) parameters in DOS FPAC 
nnnnnn.cfg file, but not lately.  I'll do that some more soon - I need to 
put a DOS computer on the bench with FPAC on it and start playing again.

However, Chuck has provided some possibility of promise for the LINUX FPAC 
being able to handle those dual port TNCs.  We'll be following that closely.

Thanks,

bud