EMRP effective monopole radiated power
 

Hello again everyone,

I was reading through a transmitter datasheet and it stated that it is
capable of outputting 1-50W. However, I got an email from the company
stating that it is only designed to work at 1W EMRP. Upon further
reading, I discovered that the effective monopole radiated power is the
transmitter output power multiplied by the antenna gain.

I'm a bit confused because if EMRP depends on antenna gain, then can't
the antenna be designed to have a higher gain and thus have a higher
EMRP? How can a transmitter be designed only for 1W EMRP? Does changing
the antenna design likely affect the transmitter performance?

I figured since the TX has a standard 50ohm output impedance, then as
long as I match the antenna I should not worry about VSWR going over
the max rating for the TX, no?

Thanks!

"CD" wrote
... I figured since the TX has a standard 50ohm output impedance,
then as long as I match the antenna I should not worry about
VSWR going over the max rating for the TX, no?
__________

Normally a transmitter is rated to provide some value of r-f power output
into a load having no more than 'X:1' SWR with respect to the load impedance
the tx is designed for. Such a load can be provided by a large number of
antennas of different directional gains, yielding different ERPs even though
the tx output power into each antenna type is the same.

One possible concern of the tx manufacturer for ERP might be related to how
well his product is shielded. But such a concern probably indicates a
rather inferior design.

RF

On 2 Sep 2005 06:44:29 -0700, "CD" wrote:

Hello again everyone,

I was reading through a transmitter datasheet and it stated that it is
capable of outputting 1-50W. However, I got an email from the company
stating that it is only designed to work at 1W EMRP. Upon further
reading, I discovered that the effective monopole radiated power is the
transmitter output power multiplied by the antenna gain.

I'm a bit confused because if EMRP depends on antenna gain, then can't
the antenna be designed to have a higher gain and thus have a higher
EMRP? How can a transmitter be designed only for 1W EMRP? Does changing
the antenna design likely affect the transmitter performance?

I figured since the TX has a standard 50ohm output impedance, then as
long as I match the antenna I should not worry about VSWR going over
the max rating for the TX, no?

I'm guessing that you aren't a ham or that if you are this transmitter
is specified for some other service that is regulated to 1 W erp.
With an efficient antenna the transmitter output should be limited;
with a less efficient antenna the transmitter has reserve capability
to overcome the inefficiency.

Just a guess...

Why don'tcha share with us the rest of the story.
What brand and model number is the transmitter you speak of.