UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - JRC NRD515 HF Coms Receiver, 1982, FM on VFO?

G0HZU_JMR · 7th Aug 2018, 9:16 pm

I think as a final check it would be worth taking a receiver wav file at the top and the bottom of the Digital VFO range to see if the loop response changes much across the range of the Digital VFO.

One thing in its favour is that the maximum division ratio N corresponds with the lowest VCO frequency (because of the mixer in the loop) and I'd expect the VCO tuning gain (in MHz/V) to slowly increase towards the lower end of its frequency range. So there will be some cancellation of the effect of increasing N here I think. But it's still worth having a look at both ends of the range to make sure the small amount of loop peaking doesn't worsen enough to cause a problem across the tuning range.

7th Aug 2018, 9:16 pm	#55
G0HZU_JMR Dekatron Join Date: Sep 2010 Location: Cheltenham, Gloucestershire, UK. Posts: 3,077	Re: JRC NRD515 HF Coms Receiver, 1982, FM on VFO? I think as a final check it would be worth taking a receiver wav file at the top and the bottom of the Digital VFO range to see if the loop response changes much across the range of the Digital VFO. One thing in its favour is that the maximum division ratio N corresponds with the lowest VCO frequency (because of the mixer in the loop) and I'd expect the VCO tuning gain (in MHz/V) to slowly increase towards the lower end of its frequency range. So there will be some cancellation of the effect of increasing N here I think. But it's still worth having a look at both ends of the range to make sure the small amount of loop peaking doesn't worsen enough to cause a problem across the tuning range. __________________ Regards, Jeremy G0HZU