Off frequency

[jazzboypro]

Hello all, i use a R8600 and a W6LVP loop to listen to MW and shortwave radio. I have noticed that most of the time a hear the radio station better if i tune a bit below or above the specided frequency. As a example i'm listening a radio station that is local to me. The frequency is 1280 Khz but i hear it much better if i tune 1277 or 1282.

Just wandering if this is normal.

Many thanks
73
VA2FCS

 

[bearcatrp]

Conditions distort the frequencies. Have noticed this with my R75.

 

[krokus]

Hello all, i use a R8600 and a W6LVP loop to listen to MW and shortwave radio. I have noticed that most of the time a hear the radio station better if i tune a bit below or above the specided frequency. As a example i'm listening a radio station that is local to me. The frequency is 1280 Khz but i hear it much better if i tune 1277 or 1282.

Just wandering if this is normal.

Many thanks
73
VA2FCS

Have you noticed if the offset is the same amount? All above or all below or random? Is it the same in the same range?

 

[Token]

Hello all, i use a R8600 and a W6LVP loop to listen to MW and shortwave radio. I have noticed that most of the time a hear the radio station better if i tune a bit below or above the specided frequency. As a example i'm listening a radio station that is local to me. The frequency is 1280 Khz but i hear it much better if i tune 1277 or 1282.

Just wandering if this is normal.

Many thanks
73
VA2FCS

In general, I would say this is not normal for a local AM station reception. It might happen under some conditions occasionally, but should not be the rule.

Interference from stations on either side of the target station can cause similar issues that you describe, however you say this is a local station, so that is less likely.

Does it do this in all filter widths? If you change form AM to USB or LSB does this change the results? To use USB or LSB with an AM station you will need to be on center frequency for everything to sound correct.

A recording, preferably video, of this happening may shed some light.

T!

 

[jazzboypro]

Have you noticed if the offset is the same amount? All above or all below or random? Is it the same in the same range?

Actually it sounds better 2-3 KHz above AND below the official frequency of the AM station.

In general, I would say this is not normal for a local AM station reception. It might happen under some conditions occasionally, but should not be the rule.

Interference from stations on either side of the target station can cause similar issues that you describe, however you say this is a local station, so that is less likely.

Does it do this in all filter widths? If you change form AM to USB or LSB does this change the results? To use USB or LSB with an AM station you will need to be on center frequency for everything to sound correct.

A recording, preferably video, of this happening may shed some light.

T!

Yes it does it no matter the filter i use. On USB and LSB it sounds good only when i'm on the exact frequency. On AM it sounds as if the person was holding the microphone to close. Here is another example of an AM station that is local to me.

Station frequency 730 KHz

Its sounds ok from 727 to 729 and from 731 to 733. Again on USB and LSB it sounds ok only on 730

 

[popnokick]

Are you familiar with and do you have enabled / disabled either of the following functions in the R8600?
- Notch Filter: Auto Notch or Manual Notch
- Digital Twin PBT (Passband Tuning)
These functions are on page 5-2 of your manual. Check carefully as they have major impact on tuning and what you hear (or don't hear).

 

[jazzboypro]

Are you familiar with and do you have enabled / disabled either of the following functions in the R8600?
- Notch Filter: Auto Notch or Manual Notch
- Digital Twin PBT (Passband Tuning)
These functions are on page 5-2 of your manual. Check carefully as they have major impact on tuning and what you hear (or don't hear).

Notch Filter was set to MN (wide) setting it to Off or AN solved the problem. Many thanks

 

[WA8ZTZ]

I have noticed that most of the time a hear the radio station better if i tune a bit below or above the specided frequency. As a example i'm listening a radio station that is local to me. The frequency is 1280 Khz but i hear it much better if i tune 1277 or 1282.

Just wandering if this is normal.

What you describe is normal with a receiver with narrow enough bandwidth. You actually are tuning through the signal from the lower sideband then the carrier then the upper sideband. The sidebands sound good but the exact carrier frequency not so well. This is because no information is contained in the carrier. All information is contained in the sidebands.

 

[Boombox]

What does "better" mean? More treble from the signal? I.e., more "fidelity"? That would be normal, as most of the information on a MW broadcast signal is in the sidebands. And if your radio is set to a narrower receive bandwidth, you're doing to see some of the treble response cut if you zero your receiver to the carrier frequency.

If you use an analog, analog-tuned radio and slowly tune through a station's signal you'll hear the difference instantly.

 

[jazzboypro]

What does "better" mean? More treble from the signal? I.e., more "fidelity"? That would be normal, as most of the information on a MW broadcast signal is in the sidebands. And if your radio is set to a narrower receive bandwidth, you're doing to see some of the treble response cut if you zero your receiver to the carrier frequency.

If you use an analog, analog-tuned radio and slowly tune through a station's signal you'll hear the difference instantly.

What i mean by "better" is that the quality of the sound is better. Like i said, when i was on the frequency it sounded as if the person held the microphone to close (Splashing i believe this is called).

At any rate, this behavior got away when adjusting the notch filter. Lots of good explanation in this thread.

 

[WA8ZTZ]

Tune in an AM broadcast band signal on your receiver and observe the spectrum display. Notice that the signal appears as 3 peaks with the largest peak in the center (carrier frequency) flanked by equal smaller peaks (sidebands). This shows that more of the power is contained in the carrier with lesser amount in each of the sidebands. Now look at the waterfall display below and see that the carrier displays as a solid line containing no information with equal mirror image information containing sidebands above and below the center carrier frequency.

 

[Patch42]

At any rate, this behavior got away when adjusting the notch filter. Lots of good explanation in this thread.

The notch filter is going to remove a portion of the signal. You should leave it off unless you're getting a het whine it can be used to eliminate. In manual mode you'll need to adjust the width and frequency of the notch for it to work properly.

It sounds like you had the notch on with a wide setting and zero offset. That would take out the carrier and a good portion of the signal.

 

[jazzboypro]

The notch filter is going to remove a portion of the signal. You should leave it off unless you're getting a het whine it can be used to eliminate. In manual mode you'll need to adjust the width and frequency of the notch for it to work properly.

It sounds like you had the notch on with a wide setting and zero offset. That would take out the carrier and a good portion of the signal.

The notch was effectively set to wide however my problem was not with the strength of the signal it was with the quality or fidelity of the signal.

 

[Patch42]

The notch was effectively set to wide however my problem was not with the strength of the signal it was with the quality or fidelity of the signal.

I understand. The notch filter with a wide setting is effectively cutting a big portion of the signal right out of the middle. You've got the carrier in the middle and the program content above and below the carrier. The notch is a very deep filter that cuts a "notch" out of the received signal. Ordinarily it would be very narrow and tuned to be above or below the carrier to eliminate the whine from an interfering carrier.

About the only time you'd use it on MW would be if you're getting a carrier from Europe or one of the flamethrowers in the Middle East. When I lived in Los Angeles at certain times of year one of the local stations would get interference from a station somewhere in Asia or the South Pacific. Due to the 9kHz spacing used there, there is a MW channel 2kHz above the local station. That foreign station's carrier would create a 2kHz hum when listening to the local station. It's not at all unusual for the carrier to go much further than the program content. In that case, a narrow notch filter tuned to 2kHz above the local station would have eliminated the annoying whine without detracting much from the local station program.

When you make the notch filter wide and tune it to zero offset from the tuned frequency, the filter will remove much of the program content, leaving you with only the bits that fall outside the width of the notch, resulting in a very unnatural sound. It would be effectively the same as passing the audio through a parametric equalizer and setting all frequencies below 1kHz to -90dB. (I'm guessing on the 1kHz width. I have no idea how wide your notch filter was.)