Understood.  This is 700mhz A-Block, so I'm allowed 1000W ERP in one direction and 30W ERP in the other.  I hadn't thought it through yet when I talked about amping the 30W side.

My thinking was to use the higher power channel for downlink.  I'm looking at setting Tx power to +24, adding an amp which says +22 on the spec sheet, and a 10db omni.  That puts me around 400W before cable losses, might be 300W after cables and connectors depending on the specifics.  The spec sheet claims a noise figure of "<3db", and that seems reasonable as long as it's not a lie.

In this configuration the uplink might be up to 12db weaker than the downlink, but if I have the maximum modulation level down, then I'll still have something acceptable up.   Something like 500kbps x 200kbps in a 250khz channel.


On 7/12/2018 2:57 PM, Brian Webster wrote:
Remembering also that you will likely need a balanced path so if both ends
of the link don't have the amplification you may have a problem. Amps with a
preamplifier also included have noise figures that don't always give you a
realized gain on the receive side. Using antenna gain over just
amplification to reach the max legal power is always preferable if possible
as the gain benefits you on both receive and transmit.

Thank You,
Brian Webster
Skype: Radiowebst

-----Original Message-----
From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of Robert Andrews
Sent: Thursday, July 12, 2018 2:16 PM
To: af@af.afmug.com
Subject: Re: [AFMUG] How to count amplifiers in link budget

But he said he gets 30 ERP not 30 EIRP where EIRP = 1.64 * ERP ( if he
is actually allowed 30 ERP and not 30 EIRP ).   So that would be  49.2
EIRP IF he is allowed 30 _ERP_..   so 49.2. watts would be another 2.15
db..   9.85 dbm gain antenna.  Still no need for an amp...

Please check my math and assumptions, as I _always_ stick my hand up in
class and then spit out the wrong answer...

On 07/12/2018 10:30 AM, ch...@wbmfg.com wrote:
Yep, that is how you do it.  30 watts EIRP is 44.7 dBm
5 watts is 37 dBm.  So 44.7 - 37 = 7.7 dB gain.

A 7.7 dBi antenna is pretty common.
After adding antenna gain, I don't see much room to amplify.
-----Original Message----- From: Adam Moffett Sent: Thursday, July 12,
2018 11:06 AM To: af@af.afmug.com Subject: [AFMUG] How to count
amplifiers in link budget
I'm looking at an IoT application where we're allowed 30W ERP.  The
transmitter is 5W, so even with antenna gain I have room to amplify that.

How do you count an amplifier in your link budget?  Just add the amp's
tx gain and subtract connectors, or is there more to it than that?

Strangely I've never used an amplifier.....I've never had a legal
application for one before.


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