[minima] Re: KISS Mixer Musings
- From: Dan Reynolds <on30ng@xxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Mon, 3 Mar 2014 13:05:41 -0600
OK, the $3000 question does the mixer work though?
All of you guys are W-A-Y over my head.
I just want to know if it works.
I know I'm being simplistic but I'm a simple homebrewer...
73
Dan -- KB9JLO
https://sites.google.com/site/on30ng/
On Mon, Mar 3, 2014 at 12:18 PM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
> So for more confusion, please see:
>
> http://g0mgx.blogspot.co.uk/2014/03/more-mixer-musings.html
>
> M
>
>
>
> On 03/03/2014 06:51, Mark G0MGX wrote:
>
> I certainly can and will report back....
>
> M
>
>
> On 03/03/2014 04:09, Ashhar Farhan wrote:
>
> Mark and the gang,
>
> What was the level of the 5 MHz signal into the mixer? It looks like it
> was quite a strong one. I am a little confused.
>
> 1. The first picture at
> http://2.bp.blogspot.com/-kIK-jtP4zAs/UxDN3oyTR-I/AAAAAAAAFps/DnpUkVjtnro/s1600/LO+Only.png
> shows the local oscillator at the IF port with -10dbm output. What was the
> input level at the gate? it should be around 3 v peak-to-peap to drive the
> J310s from pinch-off to full-on.
>
> 2. In the second picture with the RF signal at 5 Mhz, (
> http://2.bp.blogspot.com/-NGDTM1XUkXU/UxDOB-QrjYI/AAAAAAAAFp0/sRNKTvuGntA/s1600/LO+15M+RF.png)
> we see that a peak at 15 MHz that is 0 dbm! this is quite a high level
> (more than 1 v peak). At this level, the IIP3 will substantially contribute
> to the harmonic distortions.
>
> Can you repeat these tests with the RF signal set to a much lower level?
> Let's say around -20dbm?
>
> - f
>
>
> On Sun, Mar 2, 2014 at 3:11 AM, Joshua Blanton <jtblanton@xxxxxxxxx>wrote:
>
>> Hello Mark and group,
>>
>> I actually built this mixer a week-ish ago, and threw it up on the
>> bench for some testing - unfortunately, I did my testing on equipment at
>> work, and don't have my notes with me here, but I can speak to the
>> grounded-source behavior, I think. As a bit of background, I'm using
>> 2SK192A-BL JFETs, because I have a large supply of them in my junkbox;
>> these will have lower max Idss, but I'm seeing 9dB conversion losses so I'm
>> not losing sleep over it - what's 3dB of loss from ideal among friends? I
>> also matched the two FETs I used for Vpinchoff, but did not match for Idss,
>> under the (possibly/probably mistaken) belief that pinchoff is more
>> critical to balance in this system. I must also explain that I only built
>> the mixer, and tested with two HP8640B generators for the LO and RF/IF
>> ports, looking at the other port with a spectrum analyzer. I built the
>> mixer to be a 6m-to-20ishMHz down-conversion, so my harmonics and their
>> mixer products were not nearby, and I didn't look at them in detail.
>>
>> If you ground the sources, your input LO swing is going to cause the
>> FET gates to conduct as diodes, which will not be ideal from a noise figure
>> point of view (I believe - that's my understanding, anyway, and it makes
>> sense to me, I think). Ideally you swing your gate voltage from pinch-off
>> (FET dependent) to *just* below conduction (a diode-drop, so call it
>> 0.6-0.7V), for your best variation in impedance; that's really the goal of
>> the FET. In an ideal world the pinch-off state would conduct nothing, and
>> the on-biased state would have 0 impedance, and thus switch the signal
>> hard-on and hard-off; also ideally the transition from one state to the
>> other would be instantaneous.
>>
>> In my mixer, for some reason (that I did not explore enough to explain
>> here) my bias circuit was causing the mixer to massively increase
>> conversion losses, if I applied any bias at all, so I'm actually running my
>> mixer with no bias but include a 4.7k resistor to ground. I haven't ever
>> measured the voltage on the source, but I assume that it's floating up some
>> level based on LO drive and the Vgs conduction voltage... I believe that
>> my gates are conducting to generate this potential, which again is not
>> ideal from a mixer noise figure perspective. Most of my measurements were
>> looking at port-to-port leakage and conversion losses, but I can toss it
>> back up on the test bench and look at some of these other parameters next
>> time I have a minute at lunch. Next time I measure, I'm going to re-read
>> the section on mixer analysis in EMRFD, so that I take better measurements
>> :-)
>>
>> All in all, this is a neat mixer - it appears to be robust (I did not
>> see compression on 0dBm input signals from RF->IF or IF->RF), and is
>> certainly simple. I look forward to playing with it more as I have time.
>>
>> Josh, KB8NYP
>>
>>
>> On Sat, Mar 1, 2014 at 5:04 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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