[minima] Re: KISS Mixer Musings
- From: Mvs Sarma <mvssarma@xxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Sat, 1 Mar 2014 10:34:18 +0530
perhaps the pot can be changed to -in between the JFTs and battery feed
thro 4K7
On Sat, Mar 1, 2014 at 10:00 AM, pakdeDar <pakdedarmantaoye@xxxxxxxxx>wrote:
> How about other spec required for this kind of mixer Joe ? I learn much
> from this discussion that high JFET Idss was specified as J310, BW10 but
> not MPF102 or other General FET ..
>
> Just a question from unexperienced builder..hihi..
>
> Sudarmanta - YC1DCN
>
> Send from my TelakaspaBerrylayauw ®
>
> -----Original Message-----
> From: Joe Street <jstreet@xxxxxxxxxxxx>
> Sender: minima-bounce@xxxxxxxxxxxxx
> Date: Fri, 28 Feb 2014 23:20:37
> To: <minima@xxxxxxxxxxxxx>
> Reply-To: minima@xxxxxxxxxxxxx
> Subject: [minima] Re: KISS Mixer Musings
>
> SST/U401 VGSth matched to within 5mv
>
>
> On 28/02/2014 11:13 PM, Joe Street wrote:
> > Why not look for a monolithic pair? If they are fabricated on the
> > same substrate the characteristics should be well matched. I haven't
> > looked but surely there must be something off the shelf?
> >
> > On 28/02/2014 7:54 PM, Tayloe, Dan (NSN - US/Tempe) wrote:
> >> We need to bias the jfet channel for 50% on, 50% off. When a jfet is
> >> "on", it grounds its winding with its phasing for RF to IF transfer.
> >> Alternating jfets flips the signal to the opposite polarity. Rapidly
> >> flipping the signal polarity through this stage at the LO rate does
> >> the mixing.
> >>
> >> Thus there is no DC current, but we are trying to turn on/off AC
> >> paths. Since jfet pinch off thresholds vary so much from device to
> >> device, separate bias is best.
> >>
> >> As a matter of fact, if you had a bunch of these, it would be nice to
> >> match Idss and pinchoff voltage for these two jfets.
> >>
> >> - Dan
> >>
> >> Sent from my Windows Phone
> >>
> >> -----Original Message-----
> >> From: ext Joe Street
> >> Sent: 2/28/2014 5:10 PM
> >> To: minima@xxxxxxxxxxxxx
> >> Subject: [minima] Re: KISS Mixer Musings
> >>
> >> These FETs are not really 'biased' in the normal sense anyways because
> >> the drains are open circuit for DC so there is no bias current flowing.
> >> What you are doing is raising and lowering the potential of the whole
> >> channel. Variation in the device fabrication processes result in device
> >> to device variance in transconductance so perhaps in this strange
> >> circuit balance is more important??
> >>
> >> On 28/02/2014 4:58 PM, Tayloe, Dan (NSN - US/Tempe) wrote:
> >>> That might change the balance of the mixer, but does not change the
> >>> bias on each gate.
> >>>
> >>> - Dan
> >>>
> >>> -----Original Message-----
> >>> From: minima-bounce@xxxxxxxxxxxxx
> >>> [mailto:minima-bounce@xxxxxxxxxxxxx] On Behalf Of ext Sandeep Lohia
> >>> Sent: Friday, February 28, 2014 2:56 PM
> >>> To: minima@xxxxxxxxxxxxx
> >>> Subject: [minima] Re: KISS Mixer Musings
> >>>
> >>>
> http://4.bp.blogspot.com/-fIABMtTpyUE/Ut9yfPotc0I/AAAAAAAAAUQ/IG6TveVonrw/s1600/under+R&D.jpg
> >>>
> >>>
> >>> NOTE : not yet tested live...
> >>>
> >>>
> >>>
> >>>
> >>>> IF you have two separate bias pots,
> >>>> You could bias the two JFETs with separate pots and adjust for
> >>>> similar drain
> >>>> Just thinking about this. I remember that the transconductance of
> >>>> JFETS
> >>>> varies quite a bit so the fact that the signals are not symetrical
> >>>> might
> >>>> be due to an imbalance in the device characteristics?
> >>>>>>> Please take a look at the link and then any volunteers who can try
> >>>>>>> and explain this to me most welcome!
> >>
> >
>
>
--
Regards
Sarma
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