Some BFO ?'s now that I have some parts

[Scott]

I have everything but the varactor here now. I guess question one is (while I keep looking):


Can I sub joe diode and jane cap in series for the varactor diode? I bet it would degrade performance, what with signal to noise and all.


I did find the LM386 two places. As much trouble as it was to get a straight answer about the LM389 from my local Radio Shack, I did not ask about the LM386. Turns out they have those in stock at US$1.15 each.


I located and ordered the LM386 from MCM electronics. US # is 1.800.543.4330, minimum order is $20., or pay a handling fee ~$4. Caps from them seem to come in 5paks. I ordered three .022uF's, and got three bags of 5 caps.


Now what about winding these coils? I got 100 feet of twisted pair alarm wire, 200 feet of 22awg stranded altogether. Since I was cutting 30' off the spool anyway, I cut both halves of the pair so I can make two coils, one 4" diameter, the other 8" diameter. I made a jig for the coil and tried winding it in my lap. That did not work very well, so I mounted the jig with a single screw through the center, and then hung the wire - wound onto an empty spool- beside it. Much better. Now all I have to do is maintain tension on the wire as I spin the jig. I am starting with the ten turn, eight inch diamter coil. Right now I have four turns against the pins of the jig, with three turns laying in the valleys created by the underlying four turns, then two and one turn at the largest diameter. Would it work better if I had two layers of turns, each five turns tall? One layer of turns 10 turns tall? Ten layers, one turn tall? The plan is two fasten the turns to themselves with nylon wire ties before taking the coil off the jig and applying the insulated shield tape. I could, I guess, use a notched jig, put one turn on the inside layer, than two turns, then three, then four.


Should I maybe increase the diameter to the point I can make a nice 7 turn coil with a hexagonal cross section? It seems the length of the coil wire is supposed to be 80*pi.


Thanks,


Scott

[Carl]

Re: Some BFO ?'s now that I have some parts

>I have everything but the varactor here now. I guess question one is (while I keep looking):


>Can I sub joe diode and jane cap in series for the varactor diode? I bet it would degrade performance, what with signal to noise and all.


You might find a diode with a depletion capacitance that has a fairly strong voltage dependency, but I doubt it will be enough. If you did, it would not degrade performance. There are ways to force a Colpitts oscillator to shift by using a potentiometer. I'll try to find my notes on this.


>I did find the LM386 two places. As much trouble as it was to get a straight answer about the LM389 from my local Radio Shack, I did not ask about the LM386. Turns out they have those in stock at US$1.15 each.


>I located and ordered the LM386 from MCM electronics. US # is 1.800.543.4330, minimum order is $20., or pay a handling fee ~$4. Caps from them seem to come in 5paks. I ordered three .022uF's, and got three bags of 5 caps.


Yes, Radio Shack has the LM386 and caps. Also, they have an order line from which you can get all kinds of parts that the stores don't carry. Next time you're there get a "Tech America" catalog, now called "RadioShack.com". Lots of stuff.


>Now what about winding these coils? I got 100 feet of twisted pair alarm wire, 200 feet of 22awg stranded altogether. Since I was cutting 30' off the spool anyway, I cut both halves of the pair so I can make two coils, one 4" diameter, the other 8" diameter. I made a jig for the coil and tried winding it in my lap. That did not work very well, so I mounted the jig with a single screw through the center, and then hung the wire - wound onto an empty spool- beside it. Much better. Now all I have to do is maintain tension on the wire as I spin the jig. I am starting with the ten turn, eight inch diamter coil. Right now I have four turns against the pins of the jig, with three turns laying in the valleys created by the underlying four turns, then two and one turn at the largest diameter. Would it work better if I had two layers of turns, each five turns tall? One layer of turns 10 turns tall? Ten layers, one turn tall? The plan is two fasten the turns to themselves with nylon wire ties before taking the coil off the jig and applying the insulated shield tape. I could, I guess, use a notched jig, put one turn on the inside layer, than two turns, then three, then four.


>Should I maybe increase the diameter to the point I can make a nice 7 turn coil with a hexagonal cross section? It seems the length of the coil wire is supposed to be 80*pi.


Easiest method: put 6 nails in a piece of plywood in a hex arrangement approx. the size of the coil you want. Angle the nails slightly outward. Wind your wire around the hex, don't worry at all about how the wires lay as long as they're in a nice tight bundle. Slide some electrical tape under the coil in several places and wrap tightly. Then pull a nail out and remove the coil.


Finish wrapping the whole coil in tape TIGHTLY. You don't want any movement in the wires. Add shielding and another layer of tape.


- Carl

[rick]

Re: Some BFO ?'s now that I have some parts

the bfo is an excellent metal detector to start
with---indeed it was the only one that was able to
detect--btwn. it and the vlf of today--the fine gold
chain that is so difficult to detect (unless
balled up)...


your first post indicated your inability to
resolve the lm389 issue--and honest responces
were given.if this was still inadequit for you
simply repost your next query..there are people
here that would help you..or you simply were
not serious anyway---in which case your humor
is taken in stride---


reg-rick




>I have everything but the varactor here now. I guess question one is (while I keep looking):
>Can I sub joe diode and jane cap in series for the varactor diode? I bet it would degrade performance, what with signal to noise and all.


>I did find the LM386 two places. As much trouble as it was to get a straight answer about the LM389 from my local Radio Shack, I did not ask about the LM386. Turns out they have those in stock at US$1.15 each.


>I located and ordered the LM386 from MCM electronics. US # is 1.800.543.4330, minimum order is $20., or pay a handling fee ~$4. Caps from them seem to come in 5paks. I ordered three .022uF's, and got three bags of 5 caps.


>Now what about winding these coils? I got 100 feet of twisted pair alarm wire, 200 feet of 22awg stranded altogether. Since I was cutting 30' off the spool anyway, I cut both halves of the pair so I can make two coils, one 4" diameter, the other 8" diameter. I made a jig for the coil and tried winding it in my lap. That did not work very well, so I mounted the jig with a single screw through the center, and then hung the wire - wound onto an empty spool- beside it. Much better. Now all I have to do is maintain tension on the wire as I spin the jig. I am starting with the ten turn, eight inch diamter coil. Right now I have four turns against the pins of the jig, with three turns laying in the valleys created by the underlying four turns, then two and one turn at the largest diameter. Would it work better if I had two layers of turns, each five turns tall? One layer of turns 10 turns tall? Ten layers, one turn tall? The plan is two fasten the turns to themselves with nylon wire ties before taking the coil off the jig and applying the insulated shield tape. I could, I guess, use a notched jig, put one turn on the inside layer, than two turns, then three, then four.
>Should I maybe increase the diameter to the point I can make a nice 7 turn coil with a hexagonal cross section? It seems the length of the coil wire is supposed to be 80*pi.
>Thanks,
>Scott

[rick]

Re: Some BFO ?'s now that I have some parts

hi carl--


we must be on same time---


see told you scott...


>>I have everything but the varactor here now. I guess question one is (while I keep looking):
>>Can I sub joe diode and jane cap in series for the varactor diode? I bet it would degrade performance, what with signal to noise and all.


>You might find a diode with a depletion capacitance that has a fairly strong voltage dependency, but I doubt it will be enough. If you did, it would not degrade performance. There are ways to force a Colpitts oscillator to shift by using a potentiometer. I'll try to find my notes on this.


>>I did find the LM386 two places. As much trouble as it was to get a straight answer about the LM389 from my local Radio Shack, I did not ask about the LM386. Turns out they have those in stock at US$1.15 each.


>>I located and ordered the LM386 from MCM electronics. US # is 1.800.543.4330, minimum order is $20., or pay a handling fee ~$4. Caps from them seem to come in 5paks. I ordered three .022uF's, and got three bags of 5 caps.


>Yes, Radio Shack has the LM386 and caps. Also, they have an order line from which you can get all kinds of parts that the stores don't carry. Next time you're there get a "Tech America" catalog, now called "RadioShack.com". Lots of stuff.


>>Now what about winding these coils? I got 100 feet of twisted pair alarm wire, 200 feet of 22awg stranded altogether. Since I was cutting 30' off the spool anyway, I cut both halves of the pair so I can make two coils, one 4" diameter, the other 8" diameter. I made a jig for the coil and tried winding it in my lap. That did not work very well, so I mounted the jig with a single screw through the center, and then hung the wire - wound onto an empty spool- beside it. Much better. Now all I have to do is maintain tension on the wire as I spin the jig. I am starting with the ten turn, eight inch diamter coil. Right now I have four turns against the pins of the jig, with three turns laying in the valleys created by the underlying four turns, then two and one turn at the largest diameter. Would it work better if I had two layers of turns, each five turns tall? One layer of turns 10 turns tall? Ten layers, one turn tall? The plan is two fasten the turns to themselves with nylon wire ties before taking the coil off the jig and applying the insulated shield tape. I could, I guess, use a notched jig, put one turn on the inside layer, than two turns, then three, then four.
>>Should I maybe increase the diameter to the point I can make a nice 7 turn coil with a hexagonal cross section? It seems the length of the coil wire is supposed to be 80*pi.


>Easiest method: put 6 nails in a piece of plywood in a hex arrangement approx. the size of the coil you want. Angle the nails slightly outward. Wind your wire around the hex, don't worry at all about how the wires lay as long as they're in a nice tight bundle. Slide some electrical tape under the coil in several places and wrap tightly. Then pull a nail out and remove the coil.


>Finish wrapping the whole coil in tape TIGHTLY. You don't want any movement in the wires. Add shielding and another layer of tape.


>- Carl

[okcman]

Re: Some BFO ?'s now that I have some parts

no you cannot replace the varactor for just a diode


and a cap- the whole idea behind a varactor is that with a change in reverse bias voltage to the varactor


you have a change in capacitance- with a change in capacitance you have a shift in frequency- I base this on spending 3 years as a "oscillator/channel element" lead technician at International Crystal Man.


back engineering oscillator circuits...


The oscillator can be made variable frequency by having a variable resistor- an increase in resistance value will


lower the freq..... a decrease in resistance will raise the freq of the oscillator..... the same applies to capicitors......