Re: Yes, My homebrew µBitx now work!!


Evan Hand
 

Gerard,

Interesting matching networks.  Different from what I have seen on other sites.

On Sun, Oct 11, 2020 at 05:11 AM, Gerard wrote:
The µbitx is made of 2 rings demodulator. I read on a French forum, that we can increase performance by perfectly balancing the demodulator with a capa (Fixed or variable) for now I do not know where it should be installed. If anyone knows about this...
Not sure that I understand what a "capa" is.  Most of the balancing that I have seen use a variable resistor in place of the 50.1 resistors between the two diode bridges.  As far as I know, this is to reduce unwanted signals in the output, not improve the sensitivity or reduce the loss.


https://www.qsl.net/va3iul/RF%20Mixers/RF_Mixers.pdf


In your case, I would not start there.  Rather look to the Si5351a output.  If the trace from the Si5351a is too long, or not impedance matched (width and spacing), then the LO signal to the mixer will not be a square wave with enough amplitude to overcome the diode bias until later in the cycle.  I would see what the signal looks like on TP12, 15, and 18.  The more square the better.

You could also change to the BAT54SL or equal part for the diodes  There the pair is matched.  Or you could just go with a mixer part like the this on eBay (NOTE: I have not used this, just did a search to find one that might work):
https://www.ebay.com/i/153650913655?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=153650913655&targetid=934793860936&device=c&mktype=&googleloc=9021457&poi=&campaignid=10877432047&mkgroupid=112821775411&rlsatarget=pla-934793860936&abcId=9300402&merchantid=113735811&gclid=Cj0KCQjw2or8BRCNARIsAC_ppyamoeZI3jaNkY35f3Bvst67WJphBvLJUTuA-PDPUSPtbqV8HWetIu4aApTiEALw_wcB

The last option may be to replace the entire mixer with a module like this (NOTE: I have not used this, just did a search to find one that might work):
https://www.ebay.com/itm/SBL-3-RF-FREQUENCY-MIXERS-Double-Balanced-7-dBm-0-025-200-MHz-1PCS/132595966932?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225086%26meid%3Db52513b5ceec484eb2d85ec8dbe7a16b%26pid%3D100005%26rk%3D6%26rkt%3D12%26mehot%3Dpf%26sd%3D352803666830%26itm%3D132595966932%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b%26brand%3DMini-Circuits&_trksid=p2047675.c100005.m1851

The above are just suggestions.  Please do your research and verify before spending money or modifying your board.  Others may have alternate and or better suggestions.
73
Evan
AC9TU

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