[time-nuts] Re: Noise down-converter project

[ghf at hoffmann-hochfrequenz.de]

Am 2022-05-16 15:16, schrieb Robert LaJeunesse:
> FYI there are some rather flat video filter ICs that have been made in
> the past. The 6th order HMC1023LP5E is tunable, at its 28MHz setting
> its flat then down 0.1dB in the teens, down 0.35dB at 20 MHz. That
> same setting is 60dB down at about 90 MHz. It is also a dual part,
> designed for matched I-Q filtering.

Declared dead at DigiKey.


>> Sent: Sunday, May 15, 2022 at 5:29 PM
>> From: "ed breya" <eb at telight.com>

>> The actual filter I've been using does a good job on the higher
>> frequencies, but is poor on flatness. It has about 2-3 dB p-p passband
>> ripple, with periodicity around 5-7 MHz. I've tried various padding
>> arrangements at both ends, all of which tend to flatten it only a 
>> little
>> bit at best. Looking at it with the TG/SA setup, the character is
>> intrinsic to filter, and not due to just its reaction to the mixer and
>> cabling and such.
>> 
>> I hate building filters. Designing them in principle is easy, with all
>> sorts of available tools online, but actually rounding up the real 
>> parts
>> (and their parasitics) and physical implementation is a PITA. But, I
>> suppose I'll have to do it eventually for this project. I know how 
>> nice
>> it can be, with the right filter, but for now, I'll have to go with 
>> what
>> I have.

Did you choose a Chebyscheff design to start with? These accept some 
ripple
in the pass band, maybe some dB, to buy a steep rise of attenuation
above f-3dB.

best regards, Gerhard