MW harmonic on LW?

[unixfreak0037]

Hey all,

I've got a Sony ICF-SW7600GR. I can receive a very strong and clear signal on 252 kHz. The station identified as WCVX 1160 AM. The tower seems to be roughly a mile away from my house.

From what I've read and google'd, looks like MW harmonics end up in the SW range. So I was wondering why I can hear it way down here in LW.

Thanks.

- John

 

[w2xq]

A mile away? I have the same great portable with problems from a 50kw 640 station. Overloading, generating spurious product. If you can rotate the radio in two planes, you might be able to null WCVX... and the LW product might go away. I have to say in all the years I've owned the radio I've not found any newer portable that I would prefer.

I did find that the Sony-supplied AC adapter was letting noise on the AC line into the SW7600GR. Running the radio on batteries completely solved the problem, unmasking some otherwise weak signals. Perhaps your house wiring is acting as an antenna? Does the LW signal go away?

HTH

 

[ridgescan]

I get harmonics starting at 60kHz all the way through the LW band on my r71 and r75 from several local MWs every 10kHz-strongest on 120kHz. This is off the PAR antenna-never this bad on a straight wire.

 

[Ed_Seedhouse]

I've got a Sony ICF-SW7600GR. I can receive a very strong and clear signal on 252 kHz. The station identified as WCVX 1160 AM. The tower seems to be roughly a mile away from my house.

From what I've read and google'd, looks like MW harmonics end up in the SW range. So I was wondering why I can hear it way down here in LW.

Likely due to front end overload. These small portables generally are extremely sensitive, but also quite subject to strong signal overload.

 

[majoco]

Image interference - twice the IF frequency away from the MW station frequency.

1160 - (2 x 454) = 252

 

[Token]

Hey all,

I've got a Sony ICF-SW7600GR. I can receive a very strong and clear signal on 252 kHz. The station identified as WCVX 1160 AM. The tower seems to be roughly a mile away from my house.

From what I've read and google'd, looks like MW harmonics end up in the SW range. So I was wondering why I can hear it way down here in LW.

majoco has probably given you the correct answer here, it is probably an image issue in your radio, not a harmonic or actual signal from the transmitter.

Harmonics and spurs are sourced from the transmitting station.

A harmonic is some multiple of the transmitted frequency, for 1160 kHz you might find harmonics on 2320, 3480, 4640, 5800, etc kHz. All multiples of the 1160 kHz. A subharmonic is a possible signal that is at a frequency less than the fundamental freq, say one half the freq, but subharmonics are pretty uncommon in radio.

Spurs, or spurious emissions, are sourced from the transmitter also, but will not fall on multiples of the frequency. They are generally caused by either poor filtering in sub components of the transmitter or some undesired signals mixing in the transmitter. For example if the 1160 kHz TX has a solid state switched high Voltage supply switched at (just picking a number) 36 kHz and suffers poor HV filtering you might see the 1160 kHz signal and spurs on either or both sides offset at 36 kHz, for spurs possibly at 1124 kHz and 1196 kHz. If the fundamental is a SSB signal one of the two spurs might be inverted.

You can get image frequencies from inside your own radio via a couple different methods. You can also get images caused by external mixing of signals, not the fault of your radio or of the transmitting station, but some other external hardware that can grab two (or more) strong signals, mix them, and yield some odd results. For example I have seen poorly bonded fences near radio transmitters act as mixers and reradiate a new signal that is a mixture of the strongest fields present. I have also seen poor antenna connections at receive sites do the same thing.

T!

 

[W4OP]

Harmonics

I get harmonics starting at 60kHz all the way through the LW band on my r71 and r75 from several local MWs every 10kHz-strongest on 120kHz. This is off the PAR antenna-never this bad on a straight wire.

This is not a fault of the antenna, it's an issue with your receiver not being able to handle stronger signals- do a search of IP3 and dynamic range. Passive antennas cannot cause these issues

Dale W4OP

 

[ridgescan]

This is not a fault of the antenna, it's an issue with your receiver not being able to handle stronger signals- do a search of IP3 and dynamic range. Passive antennas cannot cause these issues

Dale W4OP

Dale, I am just reporting my experience here. Maybe it's an indication of just how powerful an antenna the PAR can be if you give it a 100' line, that it would load up both my Icoms like that-or it could well be something in my environment like Token explained, creating an image thing. When I ran that very same 100' line straight, I had no images in LW.
BTW, you can count me in on thanking you, sir, for creating such a killer SWL antenna for all of us. I still pull in many Canadian NDBs way better on the PAR in spite of it, and SW BCs boom in here 3-4 s-units better than straight wire.

 

[W4OP]

Dale, I am just reporting my experience here. Maybe it's an indication of just how powerful an antenna the PAR can be if you give it a 100' line, that it would load up both my Icoms like that-or it could well be something in my environment like Token explained, creating an image thing. When I ran that very same 100' line straight, I had no images in LW.
BTW, you can count me in on thanking you, sir, for creating such a killer SWL antenna for all of us. I still pull in many Canadian NDBs way better on the PAR in spite of it, and SW BCs boom in here 3-4 s-units better than straight wire.

I understand that is what you are hearing. My point was that passive antennas are linear devices (unless cores are being driven to saturation- not the case here) and therefore they cannot generate nonlinear IM, spurs, harmonics etc. Those responses are generated in either your RX RF stage or first mixer because of their inability to handle high signal levels. Receivers like the AOR 7030, are specifically designed for High IP3 numbers and thus are much less susceptible to spur generation. A passive front end preselector might be of help to you.
A 100' random wire fed directly into your RX, will not deliver the levels of RF that the same 100' wire and a stepdown UNUN (as in the EF-SWL) will.

73,

Dale W4\OP

 

[ridgescan]

I appreciate the advice I was checking your company website and I see filters but no preselectors-do you make one? If you do I'll get one of yours. Not too fond of MFJ here.

 

[majoco]

Ridgy - hunt around on EPay for a Yaesu FRT-7700 - mine works well with a pseudo PAR antenna - 66ft of wire into a 9:1 Un-un then coax to the FRT7700.

Fortunately I don't have any BC band flamethrowers nearby!

 

[W4OP]

HF Preselector

I am sorry, we do not.

Dale W4OP

 

[ridgescan]

Ridgy - hunt around on EPay for a Yaesu FRT-7700 - mine works well with a pseudo PAR antenna - 66ft of wire into a 9:1 Un-un then coax to the FRT7700.

Fortunately I don't have any BC band flamethrowers nearby!

lucky you-it's so bad here it sounds like a coffee clatch of radio people yakking in an airport restroom thanks for the suggestion-looking at one there now for $80 (is that a right deal?)

I am sorry, we do not.

Dale W4OP

That's cool Dale-I'll be a fan of your notch filters for scanners shortly

 

[majoco]

80 bucks sounds like a very good deal - grab it!

 

[greeer57]

I'm having a same problem with my Sony ICF-EX5MkII on an AM 1460 whose towers are about 3 miles away from me, I hear the station plus het tones from a semi-local 550 on 552...the radio is supposed to be double conversion, its front end isn't very strong. I did the math provided by majoco.