Re: Fix for Spurs and Harmonics on V3 Board

Dale Hardin


Harmonics.--I have already ordered the new Axiom relays, so I will try replacing the relays first.  I have a good desoldering gun, solder wick, and chipquick, so I should be ok there.  If that doesn't do the job, I can alway add the outboard relays.  Allison mentioned moving the relays to the bottom of the board, so I may add that to the fix. 

Spurs.--Also, both she and Kees mentioned moving the toroids to the bottom of the board.  I may do that first before replacing them.   I do want to do Farhan's V5 fix; it seems simple enough.

 However, I don't know if there is a local spectrum analyzer available to check the results.  I'll have to pursue that with the local ham club. I am looking at using a rtl-sdr and Spektrum as a test instrument if I can't find a local spectrum analyzer.  I already have the rtl-sdr.

As to parts, I need the replacement toroids and parts to do Farhan's V5 fix.  I assume most hams are like me and order parts like that 10 at a time (just in case).  If you have parts to spare, please contact me privately to discuss.


I don't think I will attempt the trap fix until I hear from others who have done it.

Thanks for the input, Dale

On Mon, Sep 16, 2019 at 1:30 AM iz oos <and2oosiz2@...> wrote:

About the 12mhz spur, the trap I believe is not that simple. Please let me know a good design without affecting the 30 and 20m bands. Checking it on my SDR receiver is really very low.

Il 16/set/2019 03:54, "Curt via Groups.Io" <> ha scritto:

I can speak to v3 and v4 because they are similar in this regard.

First on harmonics an effective solution involves more isolation in the relays selecting the low pass filters. I am using the external board now kitted by N8DAH. It should make your ubitx compliant on 80 to 17 meters, both cw and ssb. CW tends to be okay on these upper bands without a fix, but not ssb or data modes using the ssb math. An alternative scheme is removing the relays and replacing them with Axicom parts. This tends to be more complex work.

The remedy of the ssb spurs on the upper bands is more challenging. Possibly the Axicom relays may help here along with shielded inductors to replace the toroids at the 45 MHz crystal filter. Others add a second 45 Mhz crystal filter, but without others mods this approach doesn't work for me.

I suggest choosing one of these approaches for harmonics, and working the other matter later.


Dale Hardin
24750 State St. Unit 487
Elberta, AL 36530

Dale Hardin, KS4NS
Elberta, AL

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