Perhaps we can get back to detectors again eventually, but for now I have
had quite enough of them, so I will bite my tongue and refrain from
further comment on specific detectors for the moment.

In article , Patrick Turner
wrote:

There is adequate AGC for local stations.
The mixer and IF amps are working in their linear regions,
and the main purpose of the AGC is to prevent IF overload.

The term "local stations" as used above has also been used recently in
several other threads. I am curious what the readers of this forum would
consider to be a "local station"? What would be the range of received
field strengths that would define a "local station"? I am curious what
the range of field strengths might be that a receiver designed for "local
stations" would have to cope with?

Here in the US IIRC the FCC considers the "primary" service area of a
station to be defined by the 2 mV/M field strength contour. Also IIRC the
FCC requires a field strength of 5 uV/M for coverage of the primary City,
and recommends 20 uV/M for City coverage. One of these numbers, 2 mV/M, 5
uV/M, or 20 uV/M could probably be considered to be the lowest field
strength a "local station" would have. I will arbitrarily pick the 5 uV/M
City grade coverage number as the lower limit. At the upper end of the
scale here in the US the FCC requires 50 kW class A stations to have a
minimum unattenuated field strength of 2.56 Volts/Meter at 1 kM.
Depending on how close one wants to be to such a station and receive it
without overload, we might expect a received field strength of as much as
1,000 mV/M. Without checking the actual numbers in my notebook, which are
based on crude measurements and calculations using the local ground
conductivity and FCC propagation charts, I think the field strength of the
local 50 kW stations is about 300 uV/M in my workshop, so I will again
arbitrarily pick that number as my upper limit.

I would therefor consider a "local station" to be one having a received
field strength somewhere in the range of 5 mV/M to 300 mV/M, requiring a
receiver with total dynamic range of at least 36 dB. Does anyone have any
alternate thoughts on the meaning of "local station" as applied to
receivers?

BTW, I tried shunting the secondary of an IFT while monitoring the signal
at the primary.
As I predicted, the primary signal reduced about 1 dB.

You have said the primary signal will increase when the seconday is
shunted, ie gain will increase, but I saw no sign of that.

It will, something was screwed up in your experiment.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/