Re: New file uploaded to ultralightdx

Richard Jones

This problem is specific to the PL880. I cant speak for any other models. There are pictures and/or posts that Gary posted when he dissected both versions of the radio to try to get to the bottom of the noise that was being noticed on newer models. It appered that Tecsun ran out of or changed to a different part in newer models that was not compatible with the original shield so they just simply stopped installing the shield. Trouble is, that part was clearly an oscillator or resonator can that really should be shielded. Without the shield, noise radiates through the lcd window and is able to get picked up in the rf front end. This can be proven or expierimented with by simply placing a thumb over the window while tuning around the lf band and parts of the am band. As you might expect, the problem is more noticable in quieter locations but many times is far above the local noise floor even in noisey locations. So what can you do about this if it bothers you? Well if you are really good you could perform surgury and fashion some sort of shield. You will need to be really good though because just getting to the area requires a complete disassembly of the radio and the area to shield is small with many chances to short out traces etc. Mere mortals may want to get their hands on an older model. Somewhere there is a post that explains the location of some identifying text on the box flap otherwise there is no other way to tell. Since I'm in a unique situation of having both models supercharged and I have access to some really nice equipment, I figured I'd do a quick measurement to confirm what has been heard. Do not take the data out of context though. The plots are just relative plots in the amplitude domain. I had to put each radio within inches of an antenna that is calibrated for 1 meter to get any results at all. If you are having problems with an active antenna overloading the front end of another model, the data on that plot will not help you at all. You are going to have to keep fishing for answers one of which may be switching to a real tabletop radio with a real 50 ohm antenna input.

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