However I am a bit confused here after reading Dicks comments on your
marathon tests,in which he mentions 2.62db gain for a monopole. If this is
correct then the loss due to the environment is 5.62db not 3db.
Hello Laurie and the others,
There seems to be a bit of confusion about the 'real ERP'.
As far as I get it you have to multiply the calculated radiated power (from
the formula P = I^2*R with R = radiation resistance and I = antenna
current) with the antenna gain. The gain of a short vertical is 4.77dBi or
2.62dBd.
So assuming you put 2A into an antenna with a radiation resistance of 0.05
Ohm, you will radiate a power of 200mW. If the antenna is a short monopole
the (theoretical) ERP will be 366mW (ERP has a half-wave dipole as
reference) and the EIRP will be even 600mW (EIRP has an isotropic antenna
as reference).
CCIR Rec. 561-2 further defines EMRP where an short vertical monopole is
the reference, so in the above case you would have 200mW EMRP.
All this values are a bit theoretical as measurements performed by several
hams show that the real ERP in most cases is 3-6dB below the calculated ERP.
CEPT/ERC Recommendation 62-01 E (Mainz 1997) says :
"That the band 135.7-137.8 kHz may be used with a maximum e.r.p. of 1 Watt
on a secondary basis by the Amateur Service in CEPT countries."
So they take ERP as a reference what means that we can run 1W ERP = 1.64W
EIRP = 0.547W EMRP.
Assming that the real ERP for any 'amateur sized' antenna will be at least
3 to 6dB below the theoretical ERP the radiated power (based on P = i^2*R)
will have to exceed 1 to 2 Watt before you will reach the 1W ERP limit.
73, Rik ON7YD
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