Transmitter power questions.....

[Bob Richards]

I'll echo most of what you say, Bill.

I've seem to remember that the power was limited to 1
watt into the final output stage. Actual power
delivered to the antenna will be less than 750mW.

I have also heard that someone once measured the
output power of their transmitter by connecting a
regular power sensor in place of the antenna, and they
measured 200 or 250 mW, but I don't think that is the
proper way to measure it. A standard power sensor
usually has a 50 ohm impedance, which may not be
anything close to the actual impedance of a whip
antenna, so they won't be measuring the actual power
from the output stage.

Gain? I have no clue. Gain is relative to an isotropic
radiator (radiates equally in all directions) which is
theoretical based on the power delivered to the
antenna. The only way an antenna can have gain is if
it radiates more in one (or more) directions more than
in others. Think of an isotropic radiator as a light
bulb, and an antenna with gain as a light bulb placed
in a reflector. The more focused the beam, the higher
the gain, but less light will be radiated outside the
beam (lobe). For our purposes, we don't want a high
gain antenna, since we could end up with a null signal
in some directions.

The best way to figure the gain (if any) of our
systems would be to make EIRP or EDRP measurements
(Effective Isotropic or Dipole Radiated Power) with a
field measurement system, correlated to a calibrated
antenna. I've done this for cell phones and wireless
devices, but never one of our transmitters. (Never had
the time). IMHO, it might not be a very repeatable or
meaningful test since, in normal use, we will be
holding the radio at ??? angle to the ground. Who
wants to stand still on a turntable holding a
transmitter for the time it would take to make the
measurements at all different angles? :-) You could
place the radio on a table, but that would not be real
world.

Polarization? Depends some on the angle the antenna is
held, though I suspect it might be mostly vertical.

I'm curious why they want all of this information? I
would think they would only need to know the
frequency, bandwidth, and radiated power.

Bob R.



--- Bill Glaze <billglaze at triad.rr.com> wrote:
> I can answer a few:
> Transmitter power:  1 watt maximum.  Actual, really
> about 200 milliwatts
> Transmitter radius is difficult, because you need to
> have an effective 
> Field Strength Meter, but I have successfully
> operated an airplane's 
> controls at 1.1 miles, (line of sight) but I didn't
> intend to fly; I 
> couldn't even have seen the airplane.
> Antenna used: Vertical Whip (Normally; that's what's
> supplied)
> Antenna gain; I don't really know the answer to that
> one.
> Polarization:  Vertical  (which is normal form a
> whip antenna.)
> 
> bravo52 wrote:
> 
> > Hey Guys,
> >   I am working on a project to get RC on my Air
> Force Base and they 
> > have a few questions........  Can anybody answer
> these questions for 
> > me given a standard Futaba or JR radio? 
> >  
> > 1. What is the transmitter power?
> > 2. What is the radius the transmitter will operate
> effectively? 
> > Consider miles not Line-of-sight. (I guess that
> depends on #1)
> > 3.  What type of transmit antenna will be used,
> e.g., parabolic, whip, 
> > telescoping single pole, ect?
> > 4.  What is the transmitter antenna gain?
> > 5.  How is the transmit antenna polarized, e.g.,
> horizontal, vertical, 
> > etc.?
> >  
> > TAI
> > v/r
> > Jerry L.
> >  
> > P.S. I tried to call Tony at RS but he left 
> > early...............hmmm.......was he at the
> field????
> 
> 
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