Title: Eagle - Sparrow LNA-QSD improvements
Post by: IZ6MAF on 14. May 2020, 13:12:42
To all happy owners of Eagle - Sparrow (equipped with double balanced Tayloe Mixer) I suggest to adopt these three simple improvements:
1) As indicated by SP3OSJ, the two inputs of the OP AMP 2350UA are not balanced, (as they were designed for the mcHF single balanced mixer), it is necessary to transform the configuration to make the 2350UA work as a differential amplifier by adding the two resistors and capacitors connected to the bias, as shown in the diagrams and in the photo (Eagle).
2) The Ron of CBT3253 MIXER is flat up to about 3.3 Volts (see Ti diagram), therefore to avoid distortions in presence of strong signal it is better to lower the bias voltage to less than 1.8 volts by adding a 1.5 k resistor in parallel to the 1 K.
3) The existing polarization network of the LNA seems to work better if implemented as shown in the diagram.
'73 IZ6MAF Paolo |
Title: Re:Eagle - Sparrow LNA-QSD improvements
Post by: satoryboy on 17. December 2020, 04:37:04
| There is one small "but" - the mixer requires a high-resistance load for normal operation. If you turn on 4 repeaters on low-noise operational amplifiers before the differential amplifiers (this can be only one microcircuit case), the mixer will work as intended by the author. 73! |
Title: Re:Eagle - Sparrow LNA-QSD improvements
Post by: IZ6MAF on 19. December 2020, 07:41:45
You're right Yuri, we could have done better but we had to redesign the RF Board and adopt a scheme like the ones I am attaching which have a high impedance input. So my solution was just a fix to the current scheme.
'73 IZ6MAF Paolo |
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