winding IF coil

[radium98]

Please i need some expert Albert H or other, but please be specified without history .If i want to wind a custom coil toko 10mm to 10.7 whithout internal capacitor ,what should be the other side resonnant ?
i wound a primary and i see it is resonate @ 10.7mhz on fr meter between 1-3.what must be 4-6? ,is it the same .
thanks.

[radium98]

toko pictures

[radium98]

i uploaded 3 times the pictures < is there any issue in forum,before we could post many pictures @ once

[Albert H]

It depends what the coil is meant to do. If it's an inter-stage coupling / filter coil, the primary side will be resonant (with the right capacitor) at 10.7 MHz. The secondary is usually just a coupling winding - usually 5 - 10 turns to sniff off the 10.7 MHz without loading the primary side too much, so the "Q" factor remains high.

There were (very few) Toko coils that were resonant at 10.7 MHz on both sides - these were used in discriminator circuits for demodulating FM. These aren't very common.

A friend of mine needed to build some Band 1 receivers in a hurry the other day. He went to his local branch of "Superdrug" and bought six cheap FM / AM transistor radios. They cost £7.95 each. He gutted the radios, carefully de-soldering the IF coils and removing all the active components. He found that they had NJM2550 IF chips (16-pin surface-mounted), and he carefully recovered these too. The 2550 turns out to be a more modern version of the CA3189. The "front-end" transistors turned out to be low noise types, so he recovered those too.

He etched four PCBs for the receivers, and threw them together. They used a simple CMOS PLL controlling a FET LO so that a standard cheap 4MHz crystal can be used as the reference for any Band 1 frequency. Frequency selection was done by omitting diodes around a 74HCT4040 and then peaking the input filter. We put the finished receivers (boxed in small Eddystone diecast boxes) on my Radio Test Set (Schlumberger Stabilock 4031) and got fully quietening at just under 2µV input. Image rejection was -86dB, and the received bandwidth was substantially flat across 120kHz. Each receiver worked out at £19.50 in parts!

[radium98]

that is good ,but me i nned to combine the lo + the signal coming from the antenna selective amplifier ,so it is a mixer IF coil here ,so the output must resonate @ 10,7 but what about the input ?

[Albert H]

The INPUT needs to resonate at 10.7 MHz - the collector (or drain) of the mixer transistor needs to filter the mixture of incoming RF and the local oscillator to produce the 10.7 MHz and ignore the other products.

[radium98]

that mean it worklike a band pass filter in other term
thanks @Albert H.