Post by thread:[EE]: varactors vs. air variable caps and LED win

I origionally accidently didn't include the brackets around the "EE" so am re-sending this message with the correct subject. Have a project I've been working on for months now. 1st question- What is a good source for the plastic used for LED windows for the red 7 segment LED's? 2nd question- Polling for input on Varactors vs air variable capacitors. I recently purchased 16 RF tuner capacitors at $1.25ea from Electronix Express only to find that there is no such thing as a mating knob for them in the USA (they have two flat sides on the tuning shaft and a threaded hole in the center of that. Also, the shaft is extremely short). I've considered using a varactor tuned oscillator circuit with the 120pF variety. Saw a web page that uses two varactors chained together with the tuning voltage at the tie point. The circuit web page mentioned the low Q of varactors and I'm concerned about this affecting my circuit negatively. I'm aware of homebrew amateur 2meter transcievers using varactors and their usage in radio receiver tuners. Regards, Mike -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

>2nd question- Polling for input on Varactors vs air variable capacitors. >I recently purchased 16 RF tuner capacitors at $1.25ea from Electronix >Express only to find that there is no such thing as a mating knob for them >in the USA (they have two flat sides on the tuning shaft and a threaded hole >in the center of that. Also, the shaft is extremely short). I've >considered using a varactor tuned oscillator circuit with the 120pF variety. >Saw a web page that uses two varactors chained together with the tuning >voltage at the tie point. The circuit web page mentioned the low Q of >varactors and I'm concerned about this affecting my circuit negatively. >I'm aware of homebrew amateur 2meter transcievers using varactors and their >usage in radio receiver tuners. I think you should check out the Hyper-Abrupt junction Varactors that are available. I think you will find that these give a higher Q than older varactors. You do not state what frequency range you want, but if you are talking in terms of 120pF then I suspect it will be HF rather than broadcast or VHF. To get this you may need several diodes in parallel to get the capacitance you need, but it is a while since I looked at varactor data sheets so am not sure of the capacitance ranges available these days. Certainly every TV and Video tuner has them in. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Thu, 9 Aug 2001 14:31:49 -0000, you wrote: >I origionally accidently didn't include the brackets around the "EE" so am >re-sending this message with the correct subject. > >Have a project I've been working on for months now. >1st question- What is a good source for the plastic used for LED windows >for the red 7 segment LED's? >2nd question- Polling for input on Varactors vs air variable capacitors. >I recently purchased 16 RF tuner capacitors at $1.25ea from Electronix >Express only to find that there is no such thing as a mating knob for them What are the specifics of the Circuit that you are tuning? It may be limited by stuff other than the Varactors. Although you might need a DAC to drive a Varactor, they might be a lot easier to deal with. Dave -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads