Topics

Fix for Spurs and Harmonics on V3 Board

Dale Hardin
 

Curt, the pinout on the Axioms is symmetrical across the pins, so they can go on either side of the board.  I'm putting off ordering the toroids and caps for the mods in the hope that someone on the list who has done the mods will have extras available.  I would like to see a photo of the added V5 LC filter to see what is involved.  I am just about finished with some mods of a TenTec Century 21.  I added an AGC, and additional preamp, a Hi-Per-Mite filter (w/o amp) and am working on a digital dial.  With that effort and a long trip in October, I won't get to the uBitx until November.  I probably should have bought a V5 and called it a day, but I really love to build and modify stuff, so a V3 got me.  Up until about four years ago I had a nice HP spectrum analyzer, but got rid of it because I used it so little and it took up too much room.  I really appreciate your comments on this effort.  Regards, Dale 

On Mon, Sep 16, 2019 at 6:44 PM Curt via Groups.Io <wb8yyy=yahoo.com@groups.io> wrote:
Dale

Yes remnants of many experiments here on this list. Those axicom relays may get your harmonics compliant or very close. Watch pinouts before you put them on the underside, they should work okay on top side. Some added the shielded inductors on the 45 MHz crystal filters, and obtained lower mixer spurs in conjunction with those axicoms. The v5 LC filter did nothing to improve mixer spurs on my v4.

That trap idea was difficult to tune even with a spectrum analyzer, so hence came the shielded inductors.

Curt



--
Dale Hardin
24750 State St. Unit 487
Elberta, AL 36530
251-597-9256

--
Dale Hardin, KS4NS
Elberta, AL

Curt
 

Dale

Yes remnants of many experiments here on this list. Those axicom relays may get your harmonics compliant or very close. Watch pinouts before you put them on the underside, they should work okay on top side. Some added the shielded inductors on the 45 MHz crystal filters, and obtained lower mixer spurs in conjunction with those axicoms. The v5 LC filter did nothing to improve mixer spurs on my v4.

That trap idea was difficult to tune even with a spectrum analyzer, so hence came the shielded inductors.

Curt

Dale Hardin
 

Curt, 

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.

Iz-oos,

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" <wb8yyy=yahoo.com@groups.io> ha scritto:
Dale

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.

Curt



--
Dale Hardin
24750 State St. Unit 487
Elberta, AL 36530
251-597-9256

--
Dale Hardin, KS4NS
Elberta, AL

iz oos
 

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" <wb8yyy=yahoo.com@groups.io> ha scritto:
Dale

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.

Curt

Curt
 

Dale

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.

Curt

Dale Hardin
 

I soon will be the owner of a v3 board.  After having read way too much information on correcting harmonics and spurs, I think the fixes come down to (1) replacing the relays and putting said replacements on the back side of the board and (2) inserting Farhan's low pass LC filter between the 45mhz IF and the D1,D2 mixer, increasing the 45mhz IF gain (to drown out the 12mhz coming in on CLK2), and a 12mhz trap installed after that mixer.  (Whew, that was a loong sentence)  I understand the first mod, but Farhan's mods as developed in v5 are not documented in ubitx.net (I don't think).  I note that several people have requested a kit of parts to make the fix.  Would some kind soul prepare a set of instructions and BOM for Farhan's v5 fix.  Lastly, are the above fixes likely to solve the harmonics and spurs issue? I really appreciate the work that preceeds this request and hope I can get my v3 board "up to snuff".  73 Dale 

Dale Hardin, KS4NS
Elberta, AL