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 halfwave dipole as
reference) and the EIRP will be even 600mW (EIRP has an isotropic antenna
as reference).
CCIR Rec. 5612 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 36dB below the calculated ERP.
CEPT/ERC Recommendation 6201 E (Mainz 1997) says :
"That the band 135.7137.8 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
