[minima] Re: KISS Mixer Musings
- From: Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Sat, 1 Mar 2014 02:25:10 -0800
Mark,
About the adjustment: Farhan did say: "I adjust it for minimum LO leak to
rf port. - f"
You seem to be able to do that. Maybe that's all there is to it ;)
thomas
On Sat, Mar 1, 2014 at 2:04 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
> Hi Team
>
> Thanks to everyone that joined this discussion; my first conclusion after
> reading all the replies was that it seemed my pair of FETs were far from
> matched. Rather than trying to match two I simply swapped one of them for
> another one out of the FET draw.... the results are quite different.
>
> I've updated the page here:
>
> http://g0mgx.blogspot.co.uk/2014/02/kiss-mixer-musings.html
>
> but really I am finding little or no difference with 1 bias pot, two
> separate bias pots or just grounding the sources - the results are almost
> identical as far as I can see.
>
> In my test setup I have a 20M signal into the LO port, 15MHz into the RF
> and therefore am wanting either the 20-15 = 5MHz signal or the 20+15 =
> 35Mhz signal. Under all combinations of bias setup I can alter the
> amplitude of the *unwanted* signals, but make no difference to the *wanted
> *signals - they remain the same under all conditions.
>
> Mark
> G0MGX
>
>
>
> On 01/03/2014 05:45, pakdeDar wrote:
>
> Other questions to the experienced builder here according to the j310 used as
> KISS Mixer :
>
> 1. An article in the internet state that J310 was symmetric, symbolized by
> gate in the center between source and drain. On the contrary other article
> say that j310 was NOT symmetric.
>
> Q : what is the effect to interchange source and drain ? Could it be noticed
> clearly by ear ..our most sophisticated ham equipment Gift by our Creator ?
>
> I take simple solution for this case ..Just refer to the pin outline, wire
> the source to the common side and drain to the hot side.
> Am I correct ?
>
> 2. Is it possible to set jfet bias to 50 pct of and 50 pct on as Dan say
> using simple equipment such as DVM ( and ear setting of course ) but not
> using scope ? If yes, how ?
>
> I am interested to the spirit of KIS and N(ot) C(omplicated)...always
> remember Ham's spirit " Better to measure than not to measure " ( even using
> simple-homebrewed equipment )
>
> Sudarmanta - YC1DCN
>
>
> Send from my TelakaspaBerrylayauw ®
>
> -----Original Message-----
> From: Joe Street <jstreet@xxxxxxxxxxxx> <jstreet@xxxxxxxxxxxx>
> Sender: minima-bounce@xxxxxxxxxxxxx
> Date: Fri, 28 Feb 2014 23:20:37
> To: <minima@xxxxxxxxxxxxx> <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 <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!
>
>
>
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