An HF Noise Bridge
Uses as a Tuner-Tuner

Ok folks!  I don't have the schematic handy or the website that I pulled it from BUT I will
get around (eventually) to posting it up!


Well here is the LINK to the Schematic on M0PMB's website!


The purpose of this project was to be able to tune my tuner without having to transmit into the
antenna constantly causing interference on the bands.  I had been putting off this little project
for a while but decided that when I wanted to get on 60m that I had two choices, go outside and
cut a resonant dipole or just load up my 75m dipole or the vertical.  Obviously loading won!

It's not perfect but it does get me pretty close!  Anyway to some pictures!


Finished winding my first torroid! :)


Above I am mounting the project into a SONY box that was used for some audio beakout project.  I was fortunate
enough to get a number of these.   The cool part is they had lots of connectors already on the box!


Above:  I just used one screw and attached the board to an aluminum heat sink on the parts that were
already in the box.  I didn't even bother taking them out! hehehe :)  There are a lot of good parts that I
could scavenge off of the board that is in there.  If I had a larger project I could have either de-soldered
everything off of the board and mounted my new thing on standoffs on the board or cut a new board
the same size that would slide in the aluminum chassis.


Check out all of the cool stuff on the face plate!  I'm using the on/off switch and the BNC coax connectors.
Currently I'm running the thing off a 9v battery inside the case but I might eventually hook up the 12v
on the front.  Two screws and the entire project slides out or two screws on the back and I can
change the battery.   This would make a good QRP rig box!  With the two connectors I could put
in two qrp rigs and then would only have to add a toggle switch to go between the two radios and
add cw jacks and headphone jacks.    I could actually just wire up a jack to plug into that RS232 port
on the front and have the wires coming out of that go to the key and headphones.  I wouldn't have to
drill anything!


Better shot of the front.  Here you can see the two BNC to UHF adapters I've screwed on.


COMPLETE!  Check out that top hat! heh.  I cut it down later and it is flush.  The piece of coax on top
of the box has 2 resistors soldered in parallel between the center and shield to give me approximately 50 ohms
so that I can set the knob on top to 50 ohms.  I found it close, but no cigar.  I wound up using the dummy load
in my tuner to set it to 50 ohms.  Also in this shot I've added some BNC to UHF adapters.

The only down side to the thing is you HAVE to take it out of the line after you use it.  Applying RF to the
circuit could easily fry it!  I've thought about wiring it differently with a strong momentary switch so that the RF
normally bypasses the circuit unless you hold down the button.  It's on my later later list! :)
 M@
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