On Fri, 01 Oct 2004 02:33:14 GMT, "John Smith"
wrote:

Or, do these transmitters require the PI network to stay within FCC limits?

Hi John,

In the old days, this question use to appear on the FCC's serious
tests - also required math too.

You already demonstrated as much with:
If you analyze the receiving network, you will see that, if the antenna is
50 Ohms, the receiver sees 50 Ohms. So the network appears to simply be a
filter.
that meets the minimum technical requirment for coupling. All that
remains is the technical in-band/out-band issues (which segue into the
legal issues).

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Fri, 01 Oct 2004 02:33:14 GMT, "John Smith"
wrote:

Or, do these transmitters require the PI network to stay within FCC
limits?

Hi John,

In the old days, this question use to appear on the FCC's serious
tests - also required math too.

You already demonstrated as much with:
If you analyze the receiving network, you will see that, if the antenna is
50 Ohms, the receiver sees 50 Ohms. So the network appears to simply be a
filter.
that meets the minimum technical requirment for coupling. All that
remains is the technical in-band/out-band issues (which segue into the
legal issues).

73's
Richard Clark, KB7QHC

I don't understand what you're driving at here, Richard. I'm saying that an
analysis of the PI network shows that it serves no "matching" purpose if the
antenna is 50 Ohms and the receiver wants to see 50 Ohms. Its only purpose
seems to be to provide a narrow bandwidth. Does the receiver need it?
Probably not, unless there are a other transmitters in near by operating on
an adjacent frequency.

As for the transmitter, perhaps it needs a filter, perhaps not. But, is a PI
sufficient to meet any regulations if it does require a filter? Does the
transmitter not meet the regulations without it? I remember hearing that
these transmitters use SAW devices. Aren't SAW devices filters? All I'm
saying is that, if you can meet the FCC rules without the PI filter, you
don't need the filter at all.

73,
John

Hi John

SAW, surface acoustic wave, filters are not transmitter pass filters.

As for the need, that is simple: OF COURSE it needs filtering. Simply
observing the manufacturer's requirements reveals that:
In most cases, the output of the transmitter may need a low-pass LC filter to reduce harmonic emissions.
As for matching:
The output of the oscillator is derived directly from the collector of the oscillator transistor. It is, therefore, very sensitive to VSWR.
This, alone, demands filtering to reduce harmonics.

As for SAW filters. It has one, and uses it in the conventional
manner (not as an output filter) for frequency determination in the
oscillator.

73's
Richard Clark, KB7QHC