I put a DBM together last night and did some testing. The core is as the previous test indicated. 10 turns = 100 uh. My test indicated a 10 to one VFO to signal ratio to produce the best results. example 500 mv LO and 50 mv RF produces 10 mv IF. I plan to do another with more inductance and see how it effects the operation. I'm posting the construction.
|I cut 3 wires to the same length and wrap them together. |
|The wrapped cores with 3 coils .|
|Separate the wires and prepare to clean the varnish from them.|
|The wire can be soldered without stripping the varnish. The varnish will burn off IF you get the wire hot. I put a drop of solder on the bare end and work down it. You can also use a small flame to burn the varnish off. An alcohol lamp is ideal for this but a torch work too. After heating removing the soot and ash with an alcohol wipe works well. I heard of a guy using a small cup of alcohol to dip the wire in. After setting it on fire he turned it over then things went bad. The wipes are safer. |
|Use the ohmmeter to find a coil, this will be the primary twist it to ID it. Find another coil. Connect one end of it to the other end of the remaining coil.|
|Make a pin board with the layout for a diode diamond and the I/O. A piece of perf board might be better if you have some.Run a ground lead from LO and RF inputs. Connect the primaries and center taps of the secondary.|
|The remaining wires go to opposite sides of the diamond. Now all that's left is mounting the diodes.|
|I use clip leads as heat sinks. Pair the head and tail of a pair of diodes and connect them to a pin. Pair the other diodes head to tail and connect them to the opposite corner.|
|Take a head and tail and attach them to a corner.|
|connect the remaining ends to the last pin.|
|The finished product. This works well for a test bed to try the cores. The final product will probably be put in a metal box. You can attach the cores to a ground plane by soldering the ground connections to it. Then use the 4 leads that connect to the diodes as stand offs to solder the diodes to. |
I'm feeding it a 4001KHz @ 500mv and 4000KHz @ 54mv signal and getting a 1KHz @ 5mv output. (best I can remember. I should have wrote it down. I took pictures of the setup but can't read them.) Anyway it works it is not sensitive enough. I will try more turns on the coils.
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