Sangean Experimenting with my ATS-909X

[GB46]

I've been running my ATS-909X portable on AC lately, since I have no need to take it elsewhere, especially during the winter. Besides, the adapter supplies 9 VAC, not the conventional DC, because the conversion to DC is done inside the radio itself, so the adapter doesn't produce any RFI. As an experiment, I unplugged the 23-ft. reel antenna and extended the whip vertically to its full length. Surprisingly, there was no drop in signal strengths on HF, but a rather dramatic decrease in the noise level. As soon as I plugged the external antenna back in, the noise level increased without strengthening the signals, so that some of them became unreadable.

On the other hand, using just the whip and running the radio on fresh alkaline batteries results in a big drop in both the signals and the noise level. Am I right to suspect from this that the cord from the AC adapter to the radio is acting as an antenna, or maybe as a counterpoise to the whip?

The external antenna runs horizontally along an outside wall close to the ceiling on the top floor of a wood framed building. Unfortunately, that makes it parallel to the power lines outside. They are lower than the building's roof, so they're at eye level when I'm standing up. I'm in a corner suite, so I'm surrounded by power lines at the front of the building and others at right angles to them at the side of the building. Slung below them are lines from the local cable TV company. The lines are major ones supplying homes and businesses here and on adjacent streets. Since the whip is vertical, is that making it less susceptible to power line noise?

 

[Boombox]

It's possible that there is lower voltage getting to the circuitry on battery. Batteries aren't always 100%, which may explain why the overall noise and signals decreased in strength. Also, it's possible the radio is running hotter on the AC adaptor. Not all adaptors (internal or external) put out the right voltage. Some run a bit hot. I have a 9 volt wall wart that puts out almost 12 volts. Another that's closer to 11. I would also suspect that the AC adaptor is pulling in RFI from the electric wiring (which can carry RFI). Those are my guesses, anyway.

 

[GB46]

Good point about the batteries, Boombox. In fact, the rechargeable penlights must be worse, because they only have a capacity of 1.2, rather than 1.5 volts. Sangean's adapter is quite clean, and as I mentioned, it doesn't convert AC to DC, but simply supplies 9 volts AC. Conversion is done by a bridge rectifier circuit in the radio. Also, even on AC power the RFI from the electrical wiring drops significantly if I use the whip antenna vs. the 23 feet of wire, but without decreasing the signal strength of the station, which is why I think the external antenna is pulling in most of the RFI.

If I use my R75 I get much more noise. I don't have a whip antenna for that radio, however, so it's difficult to make a comparison. but I think the noise in the R75 comes in via the power supply, even though it's a linear, rather than a switching type. I'm certainly not going to resort to a big storage battery, however.

BTW, one of the reasons I run the portable on AC is that the backlight can be kept on continuously. On batteries the power saving feature shuts it off after 15 seconds of inactivity, which is really annoying at times.