Re: uBitx Unfiltered

Jerry Gaffke


Are you talking filters at the output of the rig, for use with current v3 and v4 boards?
That's likely the best bet for getting current rigs compliant.
Me, I'm ok with dropping the high bands, maybe stick with just 80,40,20m.
Killing spurs at 15m and 12m is difficult, and perhaps not worth the trouble
at our latitudes given where we're at in the sunspot cycle.

The current four transmit LPF's are sufficient for harmonic suppression if the board routing and relay scheme is clean.
Not sure what a "basic dual relay" scheme is.
I think the relay scheme of post 58293 is sufficient.

Regarding where this rig should go on v5:

Allison has said repeatedly that we need band specific band-pass filters
where we currently have one 30mhz LPF at L1,2,3,4.
She's built lots of this stuff and I respect her opinion.
That's how pretty much all reg-compliant radios are built.

But I am still very curious if we can tame the objectionable spurs with these changes:
1)   Use a PX1002 86.85mhz SAW filter instead of the 45mhz crystal filter (and appropriate transistors and transformers)
2)   Bring the local oscillators up to the required 7dBm.going into the mixers, keep mixer input signal levels 10dB below that
3)   Avoid having stuff from the power amp get into the IF amps.

If that is sufficient to bring the spurs into compliance, we keep the radio almost as simple as it is now.
The primary added complexity is additional gain required in the power amp to deal with the reduced signal from the mixers. 

Somewhat related:  Clean up layout so the BFO does not jump across the 12mhz filter.

Jerry,  KE7ER

On Sat, Sep 1, 2018 at 09:20 AM, Kees T wrote:
Since most keep talking about the need for BPFs for certain bands, I "guess" the 80m-10m uBITX direction should be a board with 6 filter capability. How about a basic dual relay switched filter board (3-1/4" x 3-7/8") with up to 6 pluggable filters, all manually selected with a 6 position rotary switch --AND-- you can add a small mux board with 2N3904 relay drivers for the filters and a CD4028B mux to go from the 3 Raduino pins to the filters. Start with the existing 111,110,100,000 and add two others when you have the code modified.

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