At work we have these "do-hickeys" that look like a regular "tee" connector.
However, it's meant to be used such that a signal passes through the "top"
of the tee while the "leg" of the tee "picks off" the signal some 10dB or so
down from the input. (The insertion loss is some fraction of a dB.) The
pick off seems to just be a wire tip coming out of the backside of the
connector (just capacitively coupled?); there's an adjustable sleeve that
lets you position this tip closer or further from the through line; moving
it closer creates better coupling, but also tends to decrease frequency
flatness. The cool thing is that all ports drive 50 ohms, and the
pick-off's output is surprisingly flat over more than an octave.

Any ideas? It's definitely not constructed the way I'd build a directional
coupler -- even though it performs a somewhat similar function --, nor a
"magic tee" (although I've only seem magic tees in the form of waveguides
and transformer-based affairs for HF).

Thanks,
---Joel Kolstad

"Joel Kolstad" wrote in message
...
At work we have these "do-hickeys" that look like a regular "tee"
connector.


We called these an "isolated T" when I worked in 2 way radio and used them
to check for receiver desense in a repeater. The through ports were placed
in the line to the antenna, while the isolated port was connected to a
signal generator on the receiver frequency. We would disable the repeat
function, turn the generator amplitude up until we got some value of
quieting in the receiver, and then re-enable the repeat function. If the
duplexer was mistuned (or was a cheap notch only type), or you had a dirty
transmitter, you would hear the noise level in the received signal rise.
The isolated port was needed so you did not transmit into the generator and
cause the magic smoke contained therein to issue forth.

Some repeaters were very quiet (Motorola for one). Others (brands will not
be mentioned but they had horns on them) often showed several dB of desense.
I spent many an hour trying to finesse a sow's ear into a silk purse by
tuning for minimum desense. Ahhhhhhhhh those were the days.....


Bob WB0POQ

In article ,
Joel Kolstad wrote:

At work we have these "do-hickeys" that look like a regular "tee" connector.
However, it's meant to be used such that a signal passes through the "top"
of the tee while the "leg" of the tee "picks off" the signal some 10dB or so
down from the input. (The insertion loss is some fraction of a dB.) The
pick off seems to just be a wire tip coming out of the backside of the
connector (just capacitively coupled?); there's an adjustable sleeve that
lets you position this tip closer or further from the through line; moving
it closer creates better coupling, but also tends to decrease frequency
flatness. The cool thing is that all ports drive 50 ohms, and the
pick-off's output is surprisingly flat over more than an octave.

Any ideas? It's definitely not constructed the way I'd build a directional
coupler -- even though it performs a somewhat similar function --, nor a
"magic tee" (although I've only seem magic tees in the form of waveguides
and transformer-based affairs for HF).

http://www.bird-electronic.com/produ...ct.aspx?id=115 is one
example of what you're talking about, I think.

It's nondirectional. Quite handy for monitoring RF (one of these plus
a cheap used low-bandwidth Tek oscilloscope makes a decent HF station
monitor) and for signal injection (e.g. IMD, desense testing).

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

A "do-hickey" by anyother name is still a "do-hickey"! Therefore a "T"
is a "T". No matter what "et-al" say.

Butch said this!



Joel Kolstad wrote:
At work we have these "do-hickeys" that look like a regular "tee" connector.
However, it's meant to be used such that a signal passes through the "top"
of the tee while the "leg" of the tee "picks off" the signal some 10dB or so
down from the input. (The insertion loss is some fraction of a dB.) The
pick off seems to just be a wire tip coming out of the backside of the
connector (just capacitively coupled?); there's an adjustable sleeve that
lets you position this tip closer or further from the through line; moving
it closer creates better coupling, but also tends to decrease frequency
flatness. The cool thing is that all ports drive 50 ohms, and the
pick-off's output is surprisingly flat over more than an octave.

Any ideas? It's definitely not constructed the way I'd build a directional
coupler -- even though it performs a somewhat similar function --, nor a
"magic tee" (although I've only seem magic tees in the form of waveguides
and transformer-based affairs for HF).

Thanks,
---Joel Kolstad