Adding an IF output
 

I have an IC-290A to which I'd like to add a 10.7mhz IF output. I need
bandwidth of about 1mhz and it appears the best place to get this
signal is off of the mixer output pin. How should this output be
coupled to the mixer output? Is any isolation necessary? What should
I know before I attempt this? (I can solder well, etc...)
73s,
David Carr
KD5QGR

You could use a JFET in self-biased mode. I would use a 100k series resistor
to feed the gate of the JFET; these devices typically have an input C of
around 8pF. You don't want to end up detuning your mixer circuit. The 100k
resistor should provide the desired isolation.

Pete

DC wrote in message
om...
I have an IC-290A to which I'd like to add a 10.7mhz IF output. I need
bandwidth of about 1mhz and it appears the best place to get this
signal is off of the mixer output pin. How should this output be
coupled to the mixer output? Is any isolation necessary? What should
I know before I attempt this? (I can solder well, etc...)
73s,
David Carr
KD5QGR

You could use a JFET in self-biased mode. I would use a 100k series resistor
to feed the gate of the JFET; these devices typically have an input C of
around 8pF. You don't want to end up detuning your mixer circuit. The 100k
resistor should provide the desired isolation.

Pete

DC wrote in message
om...
I have an IC-290A to which I'd like to add a 10.7mhz IF output. I need
bandwidth of about 1mhz and it appears the best place to get this
signal is off of the mixer output pin. How should this output be
coupled to the mixer output? Is any isolation necessary? What should
I know before I attempt this? (I can solder well, etc...)
73s,
David Carr
KD5QGR

This would be a good question for the rec.radio.amateur.homebrew group. See
answers below.

---------

Tim Wescott, KG7LI

"DC" wrote in message
om...
I have an IC-290A to which I'd like to add a 10.7mhz IF output. I need
bandwidth of about 1mhz and it appears the best place to get this
signal is off of the mixer output pin.

Probably, if the mixer goes straight to a filter anything further into the
radio would already be filtered, so sooner is better. If the mixer is a
diode-ring and it's followed by an IF preamp then you want to go off the
output of the preamp, however.

How should this output be coupled to the mixer output?

Lightly. I don't know what mixer the IC-290A has, but if it's a diode-ring
then the impedance presented to it's output port is very important for
intermodulation performance. Furthermore the impedance seen by the IF
filters is usually critical to proper filter operation. If it's an active
mixer the 3IM performance may not be such an issue but you could still lose
gain or mess up you filter performance.

Ideally you would redesign the coupling between the mixer and the following
stage so that both the mixer and what it's attached to sees the same
impedances that they did before, but with some of the energy diverted to
your nefarious purposes. This may not be at all necessary, you may be able
to get away with just attaching a fairly high-impedance amplifier to your
mixer pin.

Is any isolation necessary? What should I know before I attempt this?
(I can solder well, etc...)

If you can get a copy get "Solid State Design for the Radio Amatuer" by
Hayward and DeMaw. That's out of print, so a second choice is "Radio
Frequency Design" by Hayward, which is currently sold by the ARRL. I have
both of these books, and they're both good for me. I've also seen
"Experimental Methods in RF Design", by Hayward, Cambell, and Larkin highly
recommended by a trustworthy source, but I can't speak for it myself. "RF
Design" has more complete technical descriptions (it would make a good
college text), but "SS Design" has many more practical examples.
"Experamental Methods" is supposed to be aimed more to the amatuer builder
than "RF Design".

73s,
David Carr
KD5QGR

This would be a good question for the rec.radio.amateur.homebrew group. See
answers below.

---------

Tim Wescott, KG7LI

"DC" wrote in message
om...
I have an IC-290A to which I'd like to add a 10.7mhz IF output. I need
bandwidth of about 1mhz and it appears the best place to get this
signal is off of the mixer output pin.

Probably, if the mixer goes straight to a filter anything further into the
radio would already be filtered, so sooner is better. If the mixer is a
diode-ring and it's followed by an IF preamp then you want to go off the
output of the preamp, however.

How should this output be coupled to the mixer output?

Lightly. I don't know what mixer the IC-290A has, but if it's a diode-ring
then the impedance presented to it's output port is very important for
intermodulation performance. Furthermore the impedance seen by the IF
filters is usually critical to proper filter operation. If it's an active
mixer the 3IM performance may not be such an issue but you could still lose
gain or mess up you filter performance.

Ideally you would redesign the coupling between the mixer and the following
stage so that both the mixer and what it's attached to sees the same
impedances that they did before, but with some of the energy diverted to
your nefarious purposes. This may not be at all necessary, you may be able
to get away with just attaching a fairly high-impedance amplifier to your
mixer pin.

Is any isolation necessary? What should I know before I attempt this?
(I can solder well, etc...)

If you can get a copy get "Solid State Design for the Radio Amatuer" by
Hayward and DeMaw. That's out of print, so a second choice is "Radio
Frequency Design" by Hayward, which is currently sold by the ARRL. I have
both of these books, and they're both good for me. I've also seen
"Experimental Methods in RF Design", by Hayward, Cambell, and Larkin highly
recommended by a trustworthy source, but I can't speak for it myself. "RF
Design" has more complete technical descriptions (it would make a good
college text), but "SS Design" has many more practical examples.
"Experamental Methods" is supposed to be aimed more to the amatuer builder
than "RF Design".

73s,
David Carr
KD5QGR