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Homebrew PTO/VFO question.
I was curious if anyone has had any experience w/ homebrewing the PTO/VFO
from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif .. I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX |
J Shrum wrote:
I was curious if anyone has had any experience w/ homebrewing the PTO/VFO from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif . I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX It's not that they're tricky to look at -- it's that they're tricky to get everything working right. This looks like it's a basically good design. It's common-source, which is a bit odd. There's no buffer indicated, which will be necessary. Really what makes VFO construction difficult is getting the thing stable with respect to nearly every effect in the known universe, and that has more to do with component selection and construction methods than it does with the schematic. If I were going to recommend a VFO I'd recommend a series-tuned colpitts. You can probably find one in the ARRL handbook and build away. If the designs look complicated it's because to be useful a VFO needs the oscillator itself, a buffer amp and usually a power amp. The schematic you have leaves off the buffer and power amplifiers; by the time you stick those on your schematic will be as complex as any other VFO design you've seen. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
J Shrum wrote:
I was curious if anyone has had any experience w/ homebrewing the PTO/VFO from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif . I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX It's not that they're tricky to look at -- it's that they're tricky to get everything working right. This looks like it's a basically good design. It's common-source, which is a bit odd. There's no buffer indicated, which will be necessary. Really what makes VFO construction difficult is getting the thing stable with respect to nearly every effect in the known universe, and that has more to do with component selection and construction methods than it does with the schematic. If I were going to recommend a VFO I'd recommend a series-tuned colpitts. You can probably find one in the ARRL handbook and build away. If the designs look complicated it's because to be useful a VFO needs the oscillator itself, a buffer amp and usually a power amp. The schematic you have leaves off the buffer and power amplifiers; by the time you stick those on your schematic will be as complex as any other VFO design you've seen. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
I think I several hours building mine from an ARRL handbook design of some
sort, then maybe a half hour a day for a couple of weeks with a 50 Watt lamp for heating and a fan for cooling until I tweaked the drift with various N750, etc. ceramic caps. A real challenge but whatever drift I have now is virtually nil . I think I quit tweaking at about 200 Hz "cold" to "warm" drift. BTW, my transmitter is a hetrodyne affair, 5.0 to 5.2 MHz VFO + keyed crystal oscillator, both feeding Mini-Circuits DBM. If you are interested, I can put to schematic what I ended up with as I need to do it anyways for my own reference. kb8tl at arrl dot net Bob |
I think I several hours building mine from an ARRL handbook design of some
sort, then maybe a half hour a day for a couple of weeks with a 50 Watt lamp for heating and a fan for cooling until I tweaked the drift with various N750, etc. ceramic caps. A real challenge but whatever drift I have now is virtually nil . I think I quit tweaking at about 200 Hz "cold" to "warm" drift. BTW, my transmitter is a hetrodyne affair, 5.0 to 5.2 MHz VFO + keyed crystal oscillator, both feeding Mini-Circuits DBM. If you are interested, I can put to schematic what I ended up with as I need to do it anyways for my own reference. kb8tl at arrl dot net Bob |
Check out this very nice PTO/VFO from WA6OTP
http://www.wa6otp.com/pto.htm "J Shrum" wrote in message ... I was curious if anyone has had any experience w/ homebrewing the PTO/VFO from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif . I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX |
Check out this very nice PTO/VFO from WA6OTP
http://www.wa6otp.com/pto.htm "J Shrum" wrote in message ... I was curious if anyone has had any experience w/ homebrewing the PTO/VFO from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif . I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX |
That PTO is actually exactly what I would want to build, however, ordering
the kit is pretty much against the point. Does anyone by chance have the schematic for the PTO/VFO by WA6OTP? "Brian" wrote in message ink.net... Check out this very nice PTO/VFO from WA6OTP http://www.wa6otp.com/pto.htm "J Shrum" wrote in message ... I was curious if anyone has had any experience w/ homebrewing the PTO/VFO from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif . I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX |
That PTO is actually exactly what I would want to build, however, ordering
the kit is pretty much against the point. Does anyone by chance have the schematic for the PTO/VFO by WA6OTP? "Brian" wrote in message ink.net... Check out this very nice PTO/VFO from WA6OTP http://www.wa6otp.com/pto.htm "J Shrum" wrote in message ... I was curious if anyone has had any experience w/ homebrewing the PTO/VFO from http://www.qrpp-i.com/projects/ka8ma...-schematic.gif . I am pretty new to homebrewing, and was wondering if anyone knew of any problems w/ this design that I may watch for. I have read that VFO's can be very tricky, but this one looks incredibly simple. I'm just looking for anyway to get out from under the rock that I'm bound to. Thanks for any input... James Shrum - KC9FFX |
"J Shrum" wrote in message ... That PTO is actually exactly what I would want to build, however, ordering the kit is pretty much against the point. Does anyone by chance have the schematic for the PTO/VFO by WA6OTP? Look he http://www.amqrp.org/kits/tin_ear/ The vfo in this simple receiver uses the same type of PTO construction. And the manual includes a schematic. 73, "PM" |
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