Discussion in 'General Announcements' started by W5KUB, Sep 24, 2017.
You will need to upgrade your license first to talk on the 630 meter band.
Getting Started on 630 metres - QSL.net
I figure it as maybe 1.1 ohm RL for my wire in the tree, realistically I'd be lucky to get it up past .8 ohm . That's with significant "hat" in the form of three wires near 40ft long.
If I'm reading this right I'm somewhere north of 1400w in for 5w EIRP out ...
Depends, you didn't mention several other factors that are important to figuring out the EIRP. The formula is:
P(EIRP) = P(TPO) * n * G(a), where:
P(TPO) is transmitter power output in watts
n is efficiency, generally calculated as R(rad) / R(feed). R(rad) is the modeled radiation resistance. R(feed) is the actual measured resistance.
G(a) is antenna gain factor, which is calculated as 10 ^ (G(dBi) / 10). G(dBi) is peak modeled gain. For a top loaded vertical, typically 2.2 - 3 dBi.
Unless you have terrible ground loss or using a very lossy, low Q loading inductor, I doubt you need anywhere near 1.4kW TPO to reach 5W EIRP.
R(feed) (RL) is barely an ohm. Even with top loading peak modeled gain is barely over unity.
Hence a bundle of watts in for 5 watts EIRP . Unless I need another cup of coffee...
@NO3M Thanks for the explanation. I did have it nearly right
If you get the losses down to a tolerable level, say 50-75 ohms, it'll only take a little over 200W to get to 5W EIRP. Getting there includes radials, ground screens, whatever you can tie into to lower ground loss and constructing your loading coil for high Q, ie. "fat", low resistance conductor, optimal form factor, away from other objects to reduce leakage paths, etc. As a general guide... anything above 100 ohms combined losses for 630M is pretty bad, 50-100 tolerable, 30-50 good, 20-30 very good, 10-20 excellent, <10 exceptional.
so base loaded with
...wound around the 110' tall 4' around the base, Douglas Fir tree out back, say 10-15 turns , tapped up from ground, extensive ground radials, couple of vacuum caps, feed it from the house with the 7/8" hard line, strip one of my commercial inverters for the active devices ...
I want to see pictures of the tree after that exercise.