Hi, All;
Thanks for the responses so far.
The intent is to produce a device that will operate within the limits of
Part 15 of FCC rules for unlicensed radiators. Somewhere in the back of my
mind the 100 mW figure floated to the top, probably as a result of the old
100 mW unlicensed CB walkie-talkies we used to play with as kids.
It is probable in this case that a 10 mW output to a corner reflector at the
transmitter site will suffice. The target is a standard residential TV
receiving antenna connected to a household distribution system. The received
signal needs to be large enough to drive a number of splitters and lengths
of coax. This would allow us to view the image on any TV in the house.
The exciter is specified to produce a 7 dBmV output into a 75 ohm load,
which I calculate to be about 2.2 mV or 67 nW. I don't believe this is
enough to drive even a corner reflector to cover the distance we need. (It's
barely enough to give a clean signal on the TV by direct coax connection!)
We have tried using a 2.4 GHz system, but we have several nearby WiFi
systems here that it interferes with. We want to get completely away from
the 2.4GHz range. My initial plan is to use UHF channel 14.
Thanks for the pointer to MiniCircuits. I've seen ads, but hadn't thought of
them. I'll look into them.
Following are excerpts from FCC Part 15 regs
(
http://wireless.fcc.gov/rules.html) that I think would apply. Note that the
allowable field strength is the same for both unintentional and intentional
radiators in the frequency range of interest.
Subpart B_Unintentional Radiators
Sec. 15.109 Radiated emission limits.
(a) Except for Class A digital devices, the field strength of
radiated emissions from unintentional radiators at a distance of 3
meters shall not exceed the following values:
[[Page 774]]
------------------------------------------------------------------------
Field
strength
Frequency of emission (MHz) (microvolts/
meter)
------------------------------------------------------------------------
30-88................................................ ..... 100
88-216............................................... ..... 150
216-960............................................... .... 200
Above 960............................................... .. 500
------------------------------------------------------------------------
Subpart C_Intentional Radiators
Sec. 15.209 Radiated emission limits; general requirements.
(a) Except as provided elsewhere in this subpart, the emissions from
an intentional radiator shall not exceed the field strength levels
specified in the following table:
------------------------------------------------------------------------
Measurement
Frequency (MHz) Field strength distance
(microvolts/meter) (meters)
------------------------------------------------------------------------
0.009-0.490...................... 2400/F(kHz) 300
0.490-1.705...................... 24000/F(kHz) 30
1.705-30.0....................... 30 30
30-88............................ 100 ** 3
88-216........................... 150 ** 3
216-960.......................... 200 ** 3
Above 960........................ 500 3
------------------------------------------------------------------------
** Except as provided in paragraph (g), fundamental emissions from
intentional radiators operating under this section shall not be
located in the frequency bands 54-72 MHz, 76-88 MHz, 174-216 MHz or
470-806 MHz. However, operation within these frequency bands is
permItted under other sections of this part, e.g., Sec. Sec. 15.231
and 15.241.
Sec. 15.23 Home-built devices.
(a) Equipment authorization is not required for devices that are not
marketed, are not constructed from a kit, and are built in quantities of
five or less for personal use.
(b) It is recognized that the individual builder of home-built
equipment may not possess the means to perform the measurements for
determining compliance with the regulations. In this case, the builder
is expected to employ good engineering practices to meet the specified
technical standards to the greatest extent practicable. The provisions
of Sec. 15.5 apply to this equipment.