Gilbert cell mixer

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Re: Gilbert cell mixer

Post by Jalex2 on Thu Feb 14, 2013 4:34 pm

Thanks , John
Sorry about the mistype on the resistance. I think I am getting close. With the 10.7 filter I saw the response a few times as I swept across the frequency. My tuning is so wide it's hard to get right on it.

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Re: Gilbert cell mixer

Post by John on Thu Feb 14, 2013 6:12 am

Sorry Jalex you are right, there are already a pair of 1.5k resistors connected internally to each collector so you dont need any externally. I have been working with a similar gilbert cell chip recently, the MC1496, which does require external resistors, and confused the two.

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Re: Gilbert cell mixer

Post by Jalex2 on Wed Feb 13, 2013 5:42 pm

Hi John
One more quick question
I was looking as the internal diagram and it shows 2 15k ohm resistors on the collectors to the output pins already. Why do I need more to VCC
The suggested output circuit does not show any either and shows the other pin left open.

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Re: Gilbert cell mixer

Post by Jalex2 on Wed Feb 13, 2013 5:05 pm

John wrote:Pins 4 and 5 are balanced push pull outputs. You can connect both of these outputs to Vcc with resistors and use a capacitor to extract the signal from one pin only, you could place a transformer primary between pin 4 and Vcc and connect pin 5 straight to Vcc, extracting the IF signal from the secondary of the transformer, or wind a transformer with a centre tapped primary with the ends connected to pins 4 and 5 and the centre tap to Vcc, again taking the IF signal from the secondary. I use this approach using a broadband transformer made from 2 ferrite beads glued together and a trifiliar winding.

If your filter is not sharp enough you will just see lots on noise and the 455kHz signal may not be visible, the mixer produces lots of other frequencies besides 455kHz.

Also bear in mind that your 455kHz filter may not provide enough bandwidth to receive the V5 signal properly as it is WBFM.
Thank You, John
That was a lot of help and gave me a lot of ideas to play with. I have a 10.7 ceramic filter circuit on it now so maybe that will make it better for the V5 signal.
I left pin 5 open and tried to take the signal from pin 4. I didn't know I needed any VCC on either of the pins. I do see lots of noise like you said though. I will try you trifiliar winding like you said too. I think I saw on Harry's pages how to make them.
I also would like to keep the parts count as low as posible.
I have another question for you when I get this to work. What I am trying for is a simple low current carrier detector switch or maybe PWM receiver.

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Re: Gilbert cell mixer

Post by John on Wed Feb 13, 2013 6:26 am

Pins 4 and 5 are balanced push pull outputs. You can connect both of these outputs to Vcc with resistors and use a capacitor to extract the signal from one pin only, you could place a transformer primary between pin 4 and Vcc and connect pin 5 straight to Vcc, extracting the IF signal from the secondary of the transformer, or wind a transformer with a centre tapped primary with the ends connected to pins 4 and 5 and the centre tap to Vcc, again taking the IF signal from the secondary. I use this approach using a broadband transformer made from 2 ferrite beads glued together and a trifiliar winding.

If your filter is not sharp enough you will just see lots on noise and the 455kHz signal may not be visible, the mixer produces lots of other frequencies besides 455kHz.

Also bear in mind that your 455kHz filter may not provide enough bandwidth to receive the V5 signal properly as it is WBFM.

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Re: Gilbert cell mixer

Post by Jalex2 on Tue Feb 12, 2013 5:32 pm

Hi
I finally got to experiment with the NE602.
I am having problems. I started using the V5 for the TX as I had one laying on the bench. Using the data sheet I wired a 7 turn coil and used it with the diagram shown for the varactor tuned circuit. It tunes from 92 to 110 on pin 7 and as I tune through the band I don't see any changes on pin 4. The antenna is a 26" wire directly on pin 1. I am not sure what I need on pin 4 to give me something I could see on the scope. Right now I have a 455Khz IF filter on it and I thought I would be able to see the 455khz on the scope.

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Re: Gilbert cell mixer

Post by Jalex2 on Thu Dec 20, 2012 6:01 pm

Hi Ivan
I am a little confused about this forum but I saw you in here.
How have you been? Thank you for your explanation of the gilbert cell. I hope to start experimenting with it soon. I was still playing with my varactor diodes and have gotten much wider bandwidth than be fore using them. I hope to be able to do this on the gilbert LO as well.

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Re: Gilbert cell mixer

Post by Jalex2 on Wed Dec 19, 2012 5:11 pm

Admin wrote:Perhaps you can share your resuylts with us? I would be very interested in the circuits and techniques you use.

Let me know if you need any help.



BR Harry
Hi Harry
I will do that.
Right now I have been playing with the varactors I got. I built your typical V5 oscillator and used a MV109 450pf and a 47 pf in series for it's tuning.
It went from 77mhz to 118 mhz with only 9 Volts and I thought that was a pretty good guess on the turn count. I haven't tried to build another receiver yet with the NE602's yet

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Re: Gilbert cell mixer

Post by Ivan on Tue Dec 18, 2012 1:42 pm

Hi Harry,
the Gilbert cell can be fed or loaded in unbalanced manner, but it then loses its great advantage - low distortion and good suppression of certain unwanted mixing products. You need no phase splitters, transformer feed is enough. If you have an opamp or differential amplifier, which can transfer at least twice the sum of both input frequencies, it can be used on the output of the Gilbert cell. This is especially convenient in the case of productdetector or mixer down to 455 KHz IF.

VBR from Ivan

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Re: Gilbert cell mixer

Post by Admin on Mon Dec 17, 2012 9:55 pm

Perhaps you can share your resuylts with us? I would be very interested in the circuits and techniques you use.

Let me know if you need any help.



BR Harry

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Re: Gilbert cell mixer

Post by Jalex2 on Mon Dec 17, 2012 9:36 pm

Hi
I don't really care if you want to change my user name. It's alright.
I have only played with simple single transistor mixers a little.
The reason I got these was I thought it looked like it had a simpler input and could be matched to the antenna easier. I also like having the oscillator inside too and thought I might be able to build really small circuits with them. Other than that I would like to build a simple FM RX I could compare with the other FM radios and regens I have here. I am hoping for something a little sharper tuning than the Regen has.
\

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Re: Gilbert cell mixer

Post by Admin on Sun Dec 16, 2012 9:26 pm

Hi Jalex,

1 - Do you want me to change your username to simply "Jalex"?

2 - As regards the Gilbert cell mixers, I have never used them at all. For me a simple mixer is passive using a pair of ferrite beads and can operate at quite high powers. The Gilbert mixers need to have two balanced inputs and cannot handle large powers, although I believe that they do provide some conversion gain.

I believe that you can ground one of the two input leads and use a non-balanced feed, otherwise you will have to fert around with phase splitters and the like.

What sort of project had you got in mind? If you want to use them for VHF then I have a cartload of 70.000MHz crystal filters and you are most welcome to have some of those. I also have a couple of hundred 11.155MHz crystals if you can do something clever with those?

But as I said, I rather favour the high-power ferrite and diode mixer since it is good for uV through to 100mW or more. It also needs no power source Very Happy

Best regards from Harry - SM0VPO

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Gilbert cell mixer

Post by Jalex2 on Sun Dec 16, 2012 5:20 pm

Hi
I bought some NE602 gilbert cells and I want to experiment with them. I would like to play around in the FM band as I have Low Power TX's around there.
I also have some MVAM 470pf AND MV209 30PF Varactor diodes to use in the tuning I want to experiment with.
Can any one here give me a few more ideas here?

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Re: Gilbert cell mixer

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