Re: SX-117 Noise Limiter fix
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Hello, Floyd,
Yes, watched the thread wander and there was some good theory put forth but not any direct answers. Don't expect anything spectacular from the early back to back diode noise limiters of yesteryear. They can chop noise peaks but are no match for the modern dsp processing available today. Do have an R4C with the noise blanker strip and it is a definite step up. The one in my Signal One CX-7A is also pretty effective but I usually resort to my W9GR outboard DSP to really knock out noise.
Glad you id'd the defective diode, which would have been my first thought. There was a suggested improvement for the CX-7 using a pair of diodes right at the antenna input. Tried it but later removed them and went with my W9GR DSP unit.
Happy hunting and see you in the pileups!
73 ... Ed, WA9GQK
On Wednesday, June 12, 2024 at 07:18:48 PM CDT, Floyd - K8AC <floydsense@...> wrote:
This started in another thread, which went off on a tangent and never answered my question.? On my SX-117, switching the Noise Limiter on resulted in the signals and background noise level just about disappearing.? I wondered what should be heard when the NL is switched on.? In my case, the problem was traced to one bad diode in the simple noise limiter circuit.? The diode wasn't shorted or open, but exhibited a resistance of 64 ohms in both directions.? That was enough to short the IF signal to ground.? With the diodes replaced, when you switch the NL on with no noise present, there is no difference in what you hear and strong nearby signals do not cause any distortion.? The original diodes are obsolete, but you can find them on eBay if you're willing to pay the price.? Or, you can use 1N459A diodes as suggested by K9AXN.? They're available from the usual suppliers.? At this time, there is no local noise here so can't evaluate how well the NL circuit functions.??
73, Floyd - K8AC
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