On Sat, 25 Aug 2007 08:31:08 -0500, Bob Miller wrote:

On Fri, 24 Aug 2007 18:50:30 -0700, Roy Lewallen
wrote:

Bob Miller wrote:

I have an Oak Hills Research WM-2 QRP Wattmeter, which includes a
0-100 milliwatt scale.

With an MFJ 269 Antenna Analyzer hooked to the transmitter side of the
wattmeter, and an MFJ dummy load hooked to the load side of the
wattmeter, I get a reading of 3 milliwatts forward, 0 milliwatts
reflected.

Not sure whether the FCC is concerned with signals at the 3 milliwatt
level...

Most if not all the part 15 rules are defined in terms of field
strength, not power. 3 mW is way, way more than enough to exceed some of
the limits on some frequencies, when connected to even a poor antenna.
For example, Part 15 shows, in 15.209, that intentional radiators aren't
allowed to produce a field strength greater than 100 uV/m (with
exceptions) at 3 meters from 30 - 88 Mhz. 3 milliwatts will produce
*1,000 times*, or 60 dB greater than, this amount when connected to an
isotropic antenna. Hook it to a dipole to get another few dB. The limit
for class A digital devices (one class of unintentional radiators) is
the same in that range, according to 15.109. So don't think that just
because you consider a signal to be QRP that it's legal.

FYI, I checked the MFJ-269 manual, and it claims: "a relatively pure
(harmonics better than -25dBc) signal of approximately 3 Vpp
(aproximately 20 milliwatts) into 50 ohms."

So my measurement of 3 milliwatts on the wattmeter could have been
low.

Bob
k5qwg



That said, I agree that chances of prosecution are zero for using these
devices unless serious and/or intentional interference results. And I
strongly agree with the folks who have said that the last thing you want
to do is force a specific ruling on the matter from the FCC.

Roy Lewallen, W7EL

During the 1960's I engineered the antenna systems that flew on the early TIROS weather satellites. The
antennas radiated both RHCP and LHCP. In the earthward direction the gain was approximately 3 dBi. At the
ground station I operated the antenna had a 16 dBd gain at the beacon frequency of 136 MHz The beacon xmtrs
output power was 5 mW. While the satellite was at maximum slant range (just over the horizon) of 1800 miles,
the signal level from the beacons was several dB over S9 on R-390 receivers with their associated frequency
down converters.

Walt,W2DU