Reception Questions

[BOBRR]

Hello,

Using a WinRadio Excalibur.

I have noticed that for quite a few foreign am stations, the best reception I can get is
when I use lsb, or usb, rather than the normal am (for normal am here, the bandwidth encompasses the whole signal). A very significant improvement, generally.

Why is this ?

And, am I correct that for the daylight hours (mine), the frequencies around perhaps 20 to 30 MHz "usually" have better propagation than the lower ones around, e.g., 5 to 10 MHz ?

And at night, it is generally better at the lower frequencies ?

Thanks,
Bob

 

[ka3jjz]

Can't help with the first question, but the second one is easy to answer.

Right now freqs higher than 20 Mhz are going to be iffy, depending on propagation. We are going into the winter months, and usually that's not the best time to be going that high. That's why a lot of broadcasters step down in frequency during this period. Of course if we get a flux level that's nice and high, that does help those higher freqs for a few days. But I think you'll find that there really isn't all that much above 20 Mhz in the broadcast world right now.

In general (again this has a great deal to do with propagation) during the winter during the day, you should likely stay below 18 Mhz or so, As you say at night, the lower freqs - below 10 Mhz or so - are your best bet. These lower freqs won't propagate very well during the day due to the D layer of the ionosphere absorbing the signal.

You should spend some time learning about propagation, and how it's effects due to the season and what is happening on the sun makes a great deal of difference in what you hear and how well. This site (from our HF propagation wiki) is a good place to start...

Propagation Primer - Flash Movie by AE4RV

Note that you will need Flash to be turned on to use this site...Mike

 

[zz0468]

...the best reception I can get is
when I use lsb, or usb, rather than the normal am...

Why is this ?

Receiver IF bandwidth will directly impact the receiver threshold (the lowest level that can be detected), with narrower bandwidths being better. In a SSB mode, the receiver bandwidth is half of bandwidth of an AM mode, at least in most receivers. This translates directly to a better signal to noise ratio for a given signal strength.

 

[majoco]

What you are effectively doing by going to USB or LSB is what is called ECSS - Exalted Carrier Single Sideband. AM signals need the carrier to retrieve the audio, but if the carrier is rapidly fading up and down your receiver gets confused - after all the carrier going up and down is the signal! By switching to sideband, your receiver ignores the carrier and inserts one of it own, eliminating the fading and the other sideband so you should get a cleaner recovered audio. Doesn't the Excalibur have an "AMS" button - my G303 does? This should provide even better results as the two sidebands are added together as well as replacing the carrier.