Re: QUESTION for All - EASY BITX - HP 2800 series Schottky Diodes for Mixer
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Gordon
Same here.? Those integrated diode IC's are a big improvement but even
ones from the same corner of the same die are probably not perfectly
matched after they have been manually soldered onto a PCB.? Even for
those it seems better to have a balancing network to insure we get the
best balance after everything is assembled.? Maybe this is just a feel-good
situation but part of optimizing a build is feeling good about how it went
together and how it was adjusted after the build.? This seems especially
true if the mixer is a 2-diode version instead of the full ring of 4 diodes.
Arv _._
In the old days, I think we used a potentiometer and maybe a variable capacitor to balance out these mixers. I¡¯ve got a Heathkit SB 102 that I soldered together as a high school kid, and it has four individual diodes and I remember nulling out the carrier
Surely it can still be successful with all of the advanced semiconductors we have now.?
?
It is always better to use diodes and transistors made on the same substrate.
I remember replacing the PA transistor on an HW-8 with a dual transistor placed in parallel, doubled the power capability and since the? two transistors were on the same substrate, they were perfectly matched. If an IC can be found with four diodes, then finding matched diodes will not be required, if done on the same substrate ... IF such a thing exists.
Bob ¡ª KK5R
On Tuesday, January 12, 2021, 8:09:17 AM EST, Cristian Radulescu via <criradul2001= [email protected]> wrote:
Hi all, Sorry to barge in like this. 12-13 years ago when I assembled my first, ugly style, BitX, I remember experimenting a lot with these mixers. What I found is, one can not match the matched mixer rings that exist, produced by various companies. What I ended up using was a diode ring IC "extracted" from a Motorola CP040 or GP300 VHF handy placed under a small shield close to the receiver part, between two trifilar transformers (obviously a mixer configuration), 8 pin IC chip produced by NEC or JRC. I am sure one can recover boards from these old handies for parts recovery. I had excellent results with it. 73's de YO3IAZ, Cristian
On Tuesday, January 12, 2021, 02:18:30 PM GMT+2, Loris IW4AJR via <lorisbollina= [email protected]> wrote:
Hi Rafael,
It will not be easy to combine four diodes, but I have to buy the BAT41s, while I have the HP2835s in the drawer (at least forty) ... I hope to be able to find two groups of 4 diodes at least very similar.
The HP gave a margin of plus or minus 20mV of Vf between two diodes in match pair, is this an acceptable term? that is, what can be the maximum deviation between two diodes for a match pair?
On Tue, Jan 12, 2021 at 12:37 PM, < rafaelgcpp@...> wrote:
Loris,
By looking at the datasheet, you can use it. The thing is you will have to match the diodes Vf very carefully. Using matched diodes like the BAT41 halfs your work!??
73
Rafael - PU1OWL
-- IW4AJR Loris
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