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G6Tanuki · 3rd Oct 2019, 8:32 pm

How much does the resonance need to be shifted?

In times-past I've tweaked various PMR stuff originally designed for 148-174MHz coverage down to 145MHz either by screwing the original tuning-slug a bit deeper into the coil than gives the resonance then screwing-in a second slug, or - for UHF stuff - soldring a couple of short wire 'tails' to the ends of the coil and bending the outer ends of these close together to provide a squib of capacitance; this was enough to drag a 440-470MHz General Electric radio down to 432MHz, and it still met the original sensitivity-specs!

3rd Oct 2019, 8:32 pm	#5
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Modifying Vintage PMR Coils How much does the resonance need to be shifted? In times-past I've tweaked various PMR stuff originally designed for 148-174MHz coverage down to 145MHz either by screwing the original tuning-slug a bit deeper into the coil than gives the resonance then screwing-in a second slug, or - for UHF stuff - soldring a couple of short wire 'tails' to the ends of the coil and bending the outer ends of these close together to provide a squib of capacitance; this was enough to drag a 440-470MHz General Electric radio down to 432MHz, and it still met the original sensitivity-specs!