[EMAIL PROTECTED] wrote: > Recently I have been building and testing my Dual Gate FET QSD idea. > I am not finished yet but one thing I was warned about was IMD. So I > decided to try a Class A bias scheme and later I will check the > harmonic distortion and other needed testings. Anyways I will continue > to build it and then see if there is a way to over come any IMD. I am > hoping Class A is the approach. I have one FET section built on the > same breadboard as I have been building a Huff & Puff VFO. The Fet I > am using can output enough power to directly feed the sound card. > > So far I have tested it for good sine wave reproduction from 1 to 30 > MHz and it passes that, next I need to test it with square waves. > > If in the end of test the FET idea does not fly then I guess I will > stick to the SA612A. I think it was Cecil or JR who mentioned sampling > the i.f. with this circuit after the mixer stage before the i.f. filter > and all of the gain. That is the idea. > > I have been looking at NTE's line of radio IC's to see what sort of > receiver ideas one can get from their line up of chips. NTE has quite > a few IC's specifically for radio. Mixers, balanced mixers, > oscillators, i.f. agc sections, etc. > > The test output of my H101 receiver's DDS will allow me to have a LO > IN that I can change the offset of by setting of the frequency by the > receiver's software. I can then determince the exact ideal offset to > be used with any QSD idea I try and then sellect the crystal or > oscillator for that DDS frequency I used. The DDS out feature is handy. > > I have wondered if there is a way that in the future one could > control a Huff & Puff VFO via a micro controler? I can not at this > moment think of how. I did hear that some folk were looking into it > and I hope I can find that info. > > Go to <http://fairradio.com/> and look up "Nida Trainer Model 130" > #NIDA 130 for $49.50 It is a breadboard trainer with power supplies > and meters and makes a nice design center. In its catalog photo it > appears to have three breadboards. I will order one here this week. > > Dan > >
Dual gate FETs should work just fine, back some time they were considered the cat's meow since they worked so well, they could handle large signals without distortion (high IP3) especially when used in a balanced circuit. While being a mixer they can also provide gain. They are a little hard to get since very few are made anymore, they were excellent for a receivers RF/IF amplifier since changing the bias on the second gate could be used to control the gain of the device, and are by nature very low noise devices. Their big gotcha is that they are incredibly sensitive to static, so are easily damaged, I would solder them in place before removing the little wire that was wrapped around the pins The SA612A will also work fine also as long as you stay within the chips input level. By they way I read that they no longer manufacture the DIP package versions, they now only make the SMT version so enjoy them while you can, I have about 20 in stock, they are handy little devices. AMD makes a much better version that sports two mixers and a built in Quadrature clock generator. You feed it a clock at 2X the receiver frequency, and it generates the Quadrature clocks for the mixers inside, it also has a much higher IP3 figures of +19dB, it cost around $4.00, it's available in SMT only. Under 20M I prefer switches, but any kind of mixer will work, just some better than others. Here is a schematic of a receiver with I/Q audio but uses a Diode Balanced Mixer, there are all kinds of possibilities out there; < http://www.hpsdr.com/Public/Parts/Clock/TMschematic.pdf > Too much fun and not enough time. -- Cecil KD5NWA www.qrpradio.com www.hpsdr.com "Sacred Cows make the best Hamburger!" Don Seglio Batuna Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/soft_radio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
