[600MRG] EIRP and FCC?

[Brian, WA1ZMS]

My 2 cents worth....

Be it 1W or 5W, the size of any amplifier really comes down to the true ERP
that one can muster.  As an example:  If you have limited space and limited
ground plane, one may end with an antenna gain of let's say -20dB.  With
that situation one might need a 100w PA to make the 1W ERP limit. Thus the
answer needs to be solved "backwards" from what one might do.

I would opine:
1) Plan your antenna.
2) Determine your grounding system with real values based on your ground
resistances which can be 80% or the radiation resistance.
3) Use SW such as EZNEC to model your antenna system and find the peak gain.
4) Use that antenna gain to determine the amount of RF power you would need
to achieve say 5W ERP.
5) Build an amp for that power level, and then a bit more.
6) Be VERY happy in the fact that your amp will be able to deliver the RF
power you need and yet still allow for poor SWR conditions.

I made the very foolish error of running a small PA at full rated Pout only
to find that a thin coating of ice or unexpected change in ground resistance
resulted in an SWR that the amplifier found offensive and thus cost me time
and $ in replacing output devices.  You'd think I'd known better. But I was
underestimating the effects of "WX" on LF antennas.  I now know better.

If you wanted a simple answer, aim for a minimum of 100w. As a post here
used to say....." tubes blush at SWR..... while FETs explode".

-Brian, WA1ZMS

-----Original Message-----
From: 600MRG [mailto:600mrg-bounces at w7ekb.com] On Behalf Of Jim Miller
Sent: Sunday, January 25, 2015 8:33 PM
To: 600mrg at w7ekb.com group
Subject: [600MRG] EIRP and FCC?

Anyone have any idea as to what the EIRP limit the FCC is likely to impose
on 630m? I'm just working through Neil's spreadsheet.

If I build a transmitter I'd like it to be consistent with the likely
eventual limit and my antenna.

73

Jim ab3cv
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