Re: Harmonic performance - SSB vs CW


MadRadioModder
 

I’m using this one  https://www.ebay.com/itm/192131587815, but it’s only because I have a 150W amp after the uBITx inside the same box.  It’s smaller than the uBITx though and has a directional coupler on board.  I would think, as others have mentioned,  Hans’s QRP-Labs modules would work as a good starting place for those looking for a cheap alternative (https://www.qrp-labs.com/lpfkit.html).  They are quite good and $4.60 each band.  I’ve used them a lot..hard to beat.  There are some other QRP radios that have good outboard filter boards that are excellent too…Kees has some kits that are very well designed.  The one at HFProjects.com is pretty good too…

 

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of m5fra2 via Groups.Io
Sent: Monday, August 6, 2018 11:39 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonic performance - SSB vs CW

 

Which after-market board is that? I would like to keep any new boards in the same case.

 

Colin – M5FRA

 

 

 

From: BITX20@groups.io <BITX20@groups.io> On Behalf Of MadRadioModder
Sent: 06 August 2018 16:45
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonic performance - SSB vs CW

 

“rip out the filters and the relays and even the TR relay (KT1-3 and K3) and route everything to an external low pass board. “

 

Yup, done, works… gains almost 30bd in suppression with a good/cheap after-market board.

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of ajparent1/KB1GMX
Sent: Monday, August 6, 2018 9:52 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Harmonic performance - SSB vs CW

 

Warren,

Not so much disagree as wow! that's terrible... can't be!  Yes, its horrific.

5 images.
NF1 is RX mode with no filters (default is 30mhz) selected and RF applied at RX amp output
and measured at antenna connector.  It is really bad!

F3.5 is TX mode, 3.5mhz filter selected.  The blow by limits us to barely 25DB at 30mhz.
F70 is tx mode, 7mhz filter selected.  Blow by limits us to maybe 25db.
F21 is tx with 21mhz filter selected. blow by limits us to about 30db at 30mhz, not impressive.
F300 is TX with last filter 30mhz, span extened to 50mhz so we can see it.  at 45mhz we
are barely 30db down.

Results, we can argue magnitude but over all the filters are unacceptable in situ.
The first one (NF1) was the one that caught my eye as its pure blow by as there is no
direct path its all random coupling.  That has to be much better before we even
consider filters.

At this point I'd rip out the filters and the relays and even the TR relay (KT1-3 and K3)
and route everything to an external low pass board.  At that point I think we have a chance
with the external board performance being unknown but for certain cannot be worse.

 

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