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

"Steve Nosko" wrote in message
...
RF sampler. RF pick-off. RF tap-off.

Great, thanks.

Flat over an octave...that's interesting.
The cap-tap usually will give a rising response.

The cap was largely balancing out some really lossy cable, I think. :-) And
"flat" to me is about +/-2dB in this case, which is a pretty crude definition,
I expect.

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

Hi Rex,

"Rex" wrote in message
...
Here's a link to one manufacturer
http://www.microlab.fxr.com/pdf/HX,HY,Hzseries.pdf

Yep, that's them alright. The one we have is the electrostatic version.

I took a closer look over a wider frequency range at its response and -- not
too surprisingly -- it's a straight line on a log-log plot (i.e., the coupling
is almost purely capacitive).

Thanks for everyone's help,
---Joel

Rex wrote:
On Fri, 10 Mar 2006 01:55:19 -0800, "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).

Here's a link to one manufacturer
http://www.microlab.fxr.com/pdf/HX,HY,Hzseries.pdf

As on their page, I've always called them samplers.

The picture shows the probe end of an electromagnetic coupler with a
wire loop to ground. The electrostatic version looks like the head of a
nail sticking out of the teflon.

Yeah. for 50-12000 MHz. 6m and above and not much use for HF, then.
Good thing they've got a feedback E-mail address, but I suspect that
they'd want lots'o'$ for a one-off modification.

--
"If God had intended us to vote, he'd have given us candidates."

"Mike Andrews" wrote in message
...
Yeah. for 50-12000 MHz. 6m and above and not much use for HF, then.

I suspect you could make your own for HF without too much difficulty by
modifying something like a SO259 tee along with a standard PL259 connector.

On the other hand, for HF you can make pretty decent directional couplers
using transformers and get a significantly flatter response if you're looking
to accurately measure signal levels.

"Joel Kolstad" wrote in message
...
Hi Rex,

"Rex" wrote in message
...
Here's a link to one manufacturer
http://www.microlab.fxr.com/pdf/HX,HY,Hzseries.pdf

Yep, that's them alright. The one we have is the electrostatic version.

I took a closer look over a wider frequency range at its response and --
not
too surprisingly -- it's a straight line on a log-log plot (i.e., the
coupling
is almost purely capacitive).

Thanks for everyone's help,
---Joel



I don't know what Butches point was....


I think I was close, no? Don't they have a number and name stamped on them?
Usually uLab does that. Google is mighty powerful in this regard.
73, Steve, K9DCI