uBITX Transceiver semi-kit build

Discussion in 'Homebrew and Kit Projects' started by KD8UYQ, Aug 14, 2018.

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  1. KD8UYQ

    KD8UYQ Ham Member QRZ Page

  2. K5MIL

    K5MIL Ham Member QRZ Page

  3. N6ALT

    N6ALT Ham Member QRZ Page

    I ordered two from that guy, and two from a different ebay seller that are from a different manufacturer. It looks like a fairly simple fix. It also sounds like Allison has determined that the si5351 outputs need to be buffered to stop minor cross talk between the outputs, I think that will be incorporated into new releases of the Raduino board. I'm no too worried about the cross talk though because it wood be an easy thing to either rebuild or replace the Raduino board at a later time.

  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    I agree. The two issues that I am going to address first are the harmonica and spurious SSB signals on the high bands. The 45Mhz crystal filters will be here in a few days so I will take on the spur fix modification first. Gordon's second relay daughter board for the LPFs are being made now and hopeful ready to purchase in the week or two.

  5. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    My eye sight seems to be getting worse every day as I wait for my cataract surgery the end of October. The entry that I posted last was done on a iPad mini so I am sorry about the harmonica instead of Harmonics which I wanted to say. "A"s look like "S" to me now that my eyesight is so blurry. Driving is becoming a lot more fun. I listen for the scraping sound then I know that I am too close. :)

    But I digress. The 45mhz crystal filter arrived today so I installed it this evening.

    First the 47 ohm resistor R27 was removed.
    R27 removed.JPG

    Using a small pistol grip Dremel tool and a very fine drill bit, a hole was drilled between the two resistor pads and the ground plane on the bottom of the circuit board. The solder mask was carefully abraided away from around the hole to solder the crystal filter's ground lead.

    Dremel drill for 45mhz filter.JPG

    Lastly, the 45mhz crystal filter is soldered in place.

    45mhz filter in place.JPG

    So does it work?

  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Some of you maybe wondering, if my eyesight is so bad how did you manage to solder that filter on the circuit board. The answer. Super Geezer Goggles!

    Anyway, does the 45mhz crystal filter work?

    10 meters at 28.8Mhz before the crystal filter was installed.

    28.8mhz before filter.jpg

    And after the filter was installed.

    28.8mhz after 45mhz filter.jpg
    About a 10dB drop in power of the worse offending harmonic compared to the fundamental frequency. That's cool by me. Please note that the output power also decreased but only by 1 watt (from 10 watts to 9 watts)

    Here is another one; 15 meters this time at 21.2mhz

    Before the 45mhz BPF was added

    21.2mhz before filter.jpg

    And after.

    21.2mhz after 45mhz filter.jpg

    I didn't note what the watt meter was saying between the snapshots but you can see that the power level at 21.2 Mhz is pretty much the same. Pretty darn good.

    20 meters; 14.2mhz (this is the band where some have noticed a substantial drop in output power). As for my uBITX board, the output power went from 12 watts down to 10 watts which is acceptable to me.

    Before filter

    14.2mhz before filter.jpg

    After crystal filter was installed.

    14.2mhz after 45mhz filter.jpg

    Thumbs up here.

    The last one that I checked was where I hang out the most, 75 meters. In this case a nice round number, 3.8mhz.

    Before filter

    3.8mhz before filter.jpg

    And after

    3.8mhz after 45mhz filter.jpg

    Now here my output power was 14 watts. decreasing to 12 watts after the crystal filter was added. Once again that is OK by me.

    One last thing, the crystal filter was added to the transmit chain and has no effect on the receive performance. Especially all of the internally generated birdies on the 10 meter band.

    The conclusion that I draw from this simple modification, at lease on my uBITX prototype setup fixture, is that it does go a long way making this transceiver more FCC compliant.

    Next up the LPF second relay mod for offending odd order harmonics.

    Good Evening
    KG5RKP and N1OOQ like this.
  7. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Me Again,
    I think I mentioned before that I was going to make an A/B switch to compare the stock electret microphone capsule that comes with the uBITX kit with the hand mic from my Icom IC-7300.

    Mic A-B box.JPG

    The signal output is significantly higher with the electret capsule BUT the on air signal reports that I receive from folks pick the Icom microphone every time. I am told that the Icom mic sounds cleaner and more clear with a punch to it that my home made mic doesn't have.

    With that in mind I took out the two tone generator and reran some tests. The before and after 45mhz crystal filter test from yesterday were conducted with me yodeling (as my wife calls it) into the home made mic while watching for peak output power to capture the screen on the SA. I betcha that I was over driving the transmitter stages and causing all sorts of spurious signals besides those that the uBITX creates internally.

    So this time I used the Icom microphone for testing and set the speaker gain on the two tone generator to give me peak transmit power as seen on the spectrum analyzer and inline watt meter but no more. Increasing the sound volume from the TT generator into the mic wouldn't increase the peak power (nominally between 8 and 10 watts depending on the band) but it would create all sorts of additional spurs.

    Here is a snapshot of the 10 meter band at 28.8 Mhz; Output power peaked but not over driven.

    28.8mhz 2ttt.jpg

    15 meters at 21.2 Mhz

    21.2mhz 2ttt.jpg

    20 meters at 14.2 Mhz

    14.2mhz 2ttt.jpg

    And lastly, 40 meters at 7.2 Mhz

    7.2mhz 2tu.jpg

    Now we're talking!

    I still have that -39dB spike at 16.150 Mhz as seen in the 10 meter screen capture but otherwise the 45mhz crystal filter fix really appears to clean up the higher bands nicely. Spurs are well below the -43dB threshold for a clean transmitter.

    I ordered the parts to build the LPF relay daughter board per Gordon Gibby's design but am waiting to order the circuit board itself as soon as they are available.

  8. N6ALT

    N6ALT Ham Member QRZ Page


    Wow! the 45Mhx filter mod really does seem to work, and it is reproducible. I received the same filters as yours over the weekend but I haven't installed it yet as I have been following the thread to see where the dust settles as far as the input/output transformers are concerned. I have the BN 2403 cores in stock, so it would be easy to construct them if I had the little boards that one of the guys is proposing. Even without the little boards I could build them Manhattan style on a little piece of copper PCB. I may just choose to just install the filter as you have done without the transformers. I have a new V4 board that I will do the mods on, and when I'm happy I will do my V3 board which is mounted in a cabinet and is being used by my bedside. Thanks for the SA pics, it tells the whole story.

  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Joel,

    I placed an order for ten BN43-2403s today and too would like to use that little board that the ham in Australia showed recently. If not I will use one of my prototype boards. I am curious to see if the impedance matching transformers improve the spur suppression even further.

    N6ALT likes this.
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    uBITX update.

    I have set my build aside for a while. There is a bunch of activity on the BIX20 website concerning the uBITX transceiver. Specifically making it FCC compliant. There are several fixes available now to address the signal spurs on the higher bands and out of spec odd ordered harmonics especially during CW operation, I have placed orders for circuit boards and components to implement modifications to the uBITX main board in order to "fix" the problems but some of the items are coming from far afield. So, in the meantime my project is on hold until parts start coming in.


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