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How figure erp of an ATAS-120 @ 30 watts?

Aug 22nd 2017, 18:54

KJ6BQM

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I did the eclipse qso from my "schacK" which is a Honda accord with a yaesu 857d driving an ATAS-120 antenna.

I made 13 qso's on digital, but the report form asks for my erp relative to a dipole.

I found a pdf saying how to calculate the erp, but I remain clueless.

Can anybody tell me how to figure it out? I don't see how it could be much different than 30 watts for the antenna at 20 meters.
Aug 23rd 2017, 10:07

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
A full size vertical with 8 radials over ground with a conductivity of 0.005 s/m and a dielectric constant of 13 has a gain of -0.3 dBi.
A rough guess might be 40% efficiency for that mobile whip at 20 meters. 30 watts *0.40=12 watts. The gain of -0.3dB is a factor of 0.93. 0.93*12=11 watts. 15 ft of RG-58 has 0.16 dB of loss, or a factor of 0.96. 0.96*11=10.6 watts.
I'd say your EIRP is around 10 watts. This calculation is only good for one significant digit.

Zack W1VT
Aug 23rd 2017, 16:56

KJ6BQM

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Thank you. I feel better now about not being able to make a qso farther than 4000 km. with an erp of ~ 10 watts

Is it a linear relationship? If i go to CW so I can bump to 100 watts on that 857d will the erp be around 30 watts?
Aug 24th 2017, 08:42

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Quote by KJ6BQM

Is it a linear relationship? If i go to CW so I can bump to 100 watts on that 857d will the erp be around 30 watts?

Yes, if you increase the power by a factor of 3 the EIRP will also increase by a factor of 3.

Zack W1VT
ARRL Senior Lab Engineer

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