2019-06-12 Plug-in Coils Pros And Cons

from FB group Regenerative Radio… Jun 13

I’ve thought about using plug-in coils, but I’ve had experience with Grid dip meters and there are a few important issues that must be dealt with.

One is, what happens to the unused coils when the equipment is not in use. They get separated from the equipment and eventually get misplaced or lost. I have seen many grid dip meters sold with missing coils. I think all grid dip meters should come with a case with holders for the coils.

The coils are removed and replaced, and can be damaged and worn from handling, not to mention wear and tear on the pins. To reduce this, most coils are made larger with heavier plastic and pins to give them durability. Sizes of radios get smaller, but small size makes it impossible to use plug-in coils. The one advantage of premade coils is they can be made to close tolerances, so the frequencies covered can be accurate. Also you save time. Both of these advantages apply to premade coils that are not plug-in.

Coils can be made with taps that reduce or eliminate the need to change the coil. These coils can be made smaller if the plugs and sockets are eliminated. I’ve often seen coils shielded, but all the plug-in coils that I’ve seen are always unshielded. I’ve never seen toroid coils or ferrite core coils that are plug-in, but it may be possible to make one. But if toroids or ferrite cores are used it’s possible to fit several in the space of a single plug-in coil, eliminating the need to change the coils and eliminating the plug and socket.

And finally, it seems to me it would be advantageous to include much more of the circuit with the plug-in coil, thus further optimizing the circuit.

All this obviously deviates from the look of the original circuits that one may be trying to duplicate. But there are many reasons why plug-in coils are seldom used anymore. I’m just pointing out a few of them.

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