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Old 25th Feb 2021, 4:04 pm   #1
G6ONEDave
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Default Modulator output peaking coil

Whilst sorting out my MC1496 modulator build project, I find that I need a peaking coil for the output. The original description is for a 6mm former with dust core, it uses 26 SWG enamelled copper wire and has a primary of 24 turns with a centre tap half way. The secondary is 3 turns overwound at the middle of the primary. I am having difficulty obtaining the 6mm coil formers but do have some 5mm coil formers. Now to my question, if I use the same wire would 28 turns with a half way centre tap on a 5mm former have the same inductance? Alternatively if I used 28 SWG instead on a 5mm former, would the original 24 turns with centre tap be OK?

The original frequency is for 45 Mhz, so I am taking it that to use this modulator at a higher frequency the coil will require less turns. ie 90 Mhz would be a total of 12 turns with a centre tap and 180 Mhz would require a 6 turn centre tapped coil. Hopefully one of you knowledgable forum guys can tell me if my thoughts are correct.

I am using diameter to obtain circumference multiplied by turns to find the length of the original wire, so may be well off the mark in my calculations. Any help appreciated, thanks.
Dave
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Old 25th Feb 2021, 4:54 pm   #2
Wendymott
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Default Re: Modulator output peaking coil

Hi Dave. Personally I would use The first option...... then "tweek" as necessary..... Its the RF. I.F output..so its not critical to start with...... try the turns you suggest and add or subtract turns as necessary..for "maximum smoke".... I am winding 10mm Toko formers at the moment....... I will finally use a 10mm Toko for the I.F from my 1496..... first mixer at 9 mhz.... when you have done it once..it gets easier. One day I might make a "turns" table for Toko types.
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Old 26th Feb 2021, 11:48 am   #3
G6ONEDave
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Default Re: Modulator output peaking coil

Hi Wendy,
Thanks for your comments. I am currently waiting for a bobbin of 26 gauge wire to arrive. I will try the extra turns to see what happens. My aim is to build a modulator with both Band I and Band II outputs, which will require 4 of the MC chips. I also want to make it channel selectable, so will eventually wind the peaking coil to the middle of each Band. Of course I might need an extra stage of gain on the output to compensate for the signal drop off at either end of each Band.

Also having looked at the thread on the Denco coils, I have ordered the pdf version of the 'Radiotron Designers Handbook' on CDRom. It could well come in handy for this and future projects.

Thanks.
Dave
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