design defect found in rtl dongle and ham it up converter

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eeprommemory
Posts: 3
Joined: Sat Apr 04, 2015 2:37 pm

design defect found in rtl dongle and ham it up converter

Post by eeprommemory » Sat Apr 04, 2015 3:06 pm

i found a design defect in the dongles there is a capacitor missing.
here is how i found the problem.
i have a bushcom HF antenna with 100feet of RG213 during strong HF conditions the whole spectrum bounces up and down real fast in SDR# and the decoded audio sounds like it has 60HZ hum in it killing the sound.
right next to the MCX connector is a diode package marked A7 (bav99) it gets real HOT.
in the rafael micro data sheet it has a 27pf capacitor then the BAV99 diodes then a 330pf capacitor.
so to fix problem i cut the track from the MCX connector installed a 27pf capacitor and problem fixed diodes cold decoded audio perfect.
my ham it up converter blew the diodes so i replaced it then put in 27pf capacitor from the SMA plug.

rtlsdrblog
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Re: design defect found in rtl dongle and ham it up converte

Post by rtlsdrblog » Wed Apr 08, 2015 12:13 am

Thanks for telling us. Odd that the diode got hot. Do you have any images etc about this mod?

rtlsdrblog
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Re: design defect found in rtl dongle and ham it up converte

Post by rtlsdrblog » Wed Apr 08, 2015 6:01 am

I was just thinking about this and it sounds like for some reason you have a DC current on the input to the dongle. That is why the BAV99 was conducting and getting hot. Adding a blocking capacitor before the BAV99 stopped the DC current. Maybe your ham-it-up is flawed and outputting is outputting DC for some reason?

eeprommemory
Posts: 3
Joined: Sat Apr 04, 2015 2:37 pm

Re: design defect found in rtl dongle and ham it up converte

Post by eeprommemory » Thu May 07, 2015 6:25 am

on strong signal days on HF i can just put a diode and a 6V light bulb on the end of the coax and it will glow.
for 27mhz i connect the dongle direct to the cable and the diode gets hot.
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eeprommemory
Posts: 3
Joined: Sat Apr 04, 2015 2:37 pm

Re: design defect found in rtl dongle and ham it up converte

Post by eeprommemory » Thu May 07, 2015 6:34 am

other mod.
hackrf \ signal hound (junk) \ ham it up converter no trim capacitor.
adding a trim capacitor to a design is not that hard or expensive.
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