[minima] Re: KISS Mixer Musings
- From: "pakdeDar" <pakdedarmantaoye@xxxxxxxxx>
- To: "Minima Group" <minima@xxxxxxxxxxxxx>
- Date: Sat, 1 Mar 2014 05:45:57 +0000
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>
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!
>>
>
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