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Re: Stone Soup

 

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Nothing logical about building a new one-off homebrew HF transceiver.
But it can be fun!

None of these are necessarily bad ideas, but here's my yeah-but's:

> 1. Tuned IFs
Both IF's are tuned by crystal filters already.

> 2. Filter the output of the LOs

Diode ring mixers are commutating switches, not exactly the same as the true multipliers of a Gilbert cell.
So work best with a square wave as the local oscillator, not a sine wave.
We could use higher levels at the local oscillator port of the mixers, perhaps just need changes to those resistors.?

3. Push-pull preamplifier ()

More gain in front of the first serious crystal filter on RX is not necessarily a good thing
for a wideband HF receiver, just makes it easier to overload on some local AM broadcast transmitter.

4. RF transistors (BFS17P)
Yes, we could use something better than 2n3904's in places.
Though using buckets of $0.02 2n3904's/mmbt3904's (at lower gain where appropriate) has a cost and stocking advantage.

5. PA redesign (normal push pull design, two stage of IRF530 ) use BFQ19S for drivers
I plan to look very hard at the G0UPL linear, sounds like it will be clean and flat and robust and cheap.

6. More filters on the output

If we're talking transmit LPF's, the only failing on the uBitx is routing there, not the filters themselves.

7. Maybe change of the mixers to JFET mixers
Perhaps, but what are we trying to solve?
Raj's result suggests the spurs are not caused by the mixers, but rather by harmonics entering the mixers
also stuff getting coupled into the IF amps from the nearby power amp due to board layout.?

Jerry, KE7ER



On Wed, Sep 5, 2018 at 09:12 AM, MadRadioModder wrote:

Don¡¯t be so obvious and logical with this group!

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toggle quoted message. . .

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From: [email protected] [mailto:[email protected]] On Behalf Of Lev
Sent: Wednesday, September 5, 2018 8:00 AM
To: [email protected]
Subject: Re: [BITX20] Stone Soup

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So why don't we create a new design? Slightly more expensive, but a good one. My thoughts:

1. Tuned IFs

2. Filter the output of the LOs

3. Push-pull preamplifier ()

4. RF transistors (BFS17P)

5. PA redesign (normal push pull design, two stage of IRF530 ) use BFQ19S for drivers

6. More filters on the output

7. Maybe change of the mixers to JFET mixers

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I started to put together my own design, so I have some sketches. I can share if you interested.
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