I am looking for a reasonably efficient method of coupling a 602 mixer
output to a 605 input at 45MHz.

I have tried a tuned circuit with coupling caps and did not get good
results. Both the 602 and 605 are working fine independently. (I tested
the 605 with a match up from 50 Ohms to 1k5).

I am wanting a receiver with around 10dB signal to noise ratio at -115
to -118dBm.
Signal frequency is 151 MHz.
1st IF is 45MHz, 2nd IF is 455kHz(+/-15 kHz bandwidth).
The input filter has a bandwidth of 6MHz.
The image should not be an issue as it is way down at 60MHz.

I don't want to loose much gain between the 602 and 605 (about 3-5dB
would be acceptable).

Thanks in advance

Regards

David

I have tried a tuned circuit with coupling caps and did not get good
results.
-----------

David,

"...did not get good results" is a very fuzzy description of the problem you
encountered. Can you be more specific?. Is the problem a sensitivity
problem? Why do you think it's an interstage coupling issue?

You don't say whether you're coupling from the '602's mixer output into the
'605's mixer input, or from the '602's mixer output into the '605's IF
input. In the former case, the 605's input resistance is in the 4.5K range
while in the latter case the input resistances is about 1.5K. The '602
output resistance is also in the 1.5K range. In either case the output/input
resistances are already close enough to be within a few dB of optimum with
just a DC blocking cap for coupling (assuming the interface is resonant). I
don't know why you weren't successful in just resonating the output of the
'602 and capacitively coupling into the '605 with a large coupling cap. Can
you tell us what values you used?

Without analyzing this in detail, I'd say that if your interstage coupling
is resonant and tight (large coupling cap), then your sensitivity
performance will probably be limited by the noise figures of the two mixers
in cascade (assuming that the tuned input circuit isn't real lossy).


Joe
W3JDR


"David" wrote in message
...
I am looking for a reasonably efficient method of coupling a 602 mixer
output to a 605 input at 45MHz.

I have tried a tuned circuit with coupling caps and did not get good
results. Both the 602 and 605 are working fine independently. (I tested
the 605 with a match up from 50 Ohms to 1k5).

I am wanting a receiver with around 10dB signal to noise ratio at -115
to -118dBm.
Signal frequency is 151 MHz.
1st IF is 45MHz, 2nd IF is 455kHz(+/-15 kHz bandwidth).
The input filter has a bandwidth of 6MHz.
The image should not be an issue as it is way down at 60MHz.

I don't want to loose much gain between the 602 and 605 (about 3-5dB would
be acceptable).

Thanks in advance

Regards

David