Ghosts in the system

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usasa
Posts: 5
Joined: Fri Dec 30, 2016 7:00 am

Ghosts in the system

Postby usasa » Wed Sep 05, 2018 2:14 pm

I have had my SDRPlay RSP2 for some time now, I was very happy with it. “TILL”!
Now on the 13.000 Mhz, +, 6.000 Mhz + and some other frequencies, I am hearing the 20 and 40 meter ham bands coming in very strong. The stations are from California mostly, I am in Colorado. Very upsetting. This happens during the daylight hours. Has something gone wrong with my RSP2? Or is this a fault with this type of radio? Or is it some sort of atmospheric conditions? Very unhappy!

Alex
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someYguy
Posts: 93
Joined: Sun Apr 10, 2016 7:12 pm

Re: Ghosts in the system

Postby someYguy » Thu Sep 06, 2018 1:47 am

I can't imagine why your RSP2 is doing that. I use an RSP1A which is essentially the same in terms of core signal processing circuitry and I do not have such ghost signals.

Has anything in your software changed? Gain settings perhaps?

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Roger
Posts: 137
Joined: Fri Dec 29, 2017 7:59 pm

Re: Ghosts in the system

Postby Roger » Thu Sep 06, 2018 2:58 am

usasa wrote:I have had my SDRPlay RSP2 for some time now, I was very happy with it. “TILL”!
Now on the 13.000 Mhz, +, 6.000 Mhz + and some other frequencies, I am hearing the 20 and 40 meter ham bands coming in very strong. The stations are from California mostly, I am in Colorado. Very upsetting. This happens during the daylight hours. Has something gone wrong with my RSP2? Or is this a fault with this type of radio? Or is it some sort of atmospheric conditions? Very unhappy!

Alex


The RSP2 will get spurious signals and images like any tuner-based radio. Where and when they occur depends on the several factors including RF and IF gain, Sample Rate, Decimation, Local Oscillator (LO) frequency and whether you are in Zero IF or Low IF mode. If you could give specific details on each of these settings I could compare it with my RSP2pro.

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usasa
Posts: 5
Joined: Fri Dec 30, 2016 7:00 am

Re: Ghosts in the system

Postby usasa » Thu Sep 06, 2018 5:46 am

Hi all!

It drives me crazy. I get it at night on 13.000 Mhz +, I get the 40 meter band (strong signals, lots of power) . I have a 100 foot 20 Ga. long wire antenna. The radio is in a copper lined case. I have SR (MHz) set to 5.0 and DEC set to 4. I have always used that setting for over a year now and I have just noticed the problem.
Any useful suggestions for improvement would be appreciated. I do love the radio. I have used SDR's before, the little dongles.

Thank you all!
Alex
USASA
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glovisol
Posts: 157
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Ghosts in the system

Postby glovisol » Thu Sep 06, 2018 3:05 pm

Hi Alex,

Most likely your problem is system overload: you can see a clear example here:

viewtopic.php?f=5&t=3436

In the enclosed PC screen:

Near overload @ 7 MHz. The S meter was above 9+40, but the PC screen collecting software reduced it while taking the picture
Example of system overload.jpg (201.03 KiB) Viewed 962 times


the overload condition is provoked by the very strong broadcasting stations on the upper end of the screen. The station at 7,285.5 is coming in at - 38 dBm, this is the limit. When one or more stages overload, the easiest thing for them to do is to produce 2° harmonics (7.1 X 2 = 14.2 MHz) which the following receiver's circuitry will see as "normal" 20 m signals.

The remedy is, after having reduced as much as possible the RF gain, a fixed attenuator betwen antenna and receiver, this is easily calculated and built with 4 resistors. If we consider the overload limit at - 38 dBm, a 20 db attenuator will bring the offending signal down to -58 dBm and overload preoducts will disappear. However you will also lose the weak signals this way. The deluxe solution is of course to use a tuneable preselector.

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usasa
Posts: 5
Joined: Fri Dec 30, 2016 7:00 am

Re: Ghosts in the system

Postby usasa » Fri Sep 07, 2018 6:27 am

Hi All!

It is not overload. Being in Colorado and most of the stations that I hear in California. Stations that are on the proper freq. come in also all come in clear never distorted. The "s" meter never reaches s-9, always below and very understandable. I have tracked it back to 40 meter band and most of the stations are running a amplifier running about 1.5 Kw. Could that have something to do with it? It just drives me nuts!!! I have been monitoring the bands for 50 years and never have I had this happen with such a strong signals. It is if they are transmitting on the freq. it self. Please do not get me wrong I love the SDRPlay it is one of the best radios I have.

For info I am feeding the radio with Cable Television 75 Ohm underground cable. It is high quality. The antenna is 100 + feet of number 10 copper wire. It works very well on HF. Thanks for the help and info it is appreciated very much.

Alex
USASA
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glovisol
Posts: 157
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Ghosts in the system

Postby glovisol » Fri Sep 07, 2018 11:27 am

While you listen to the S7/S9 Colorado stations at 14 MHz, the Californian stations transmitting hi power (1.5 kW) are OVERLOADING your WIDEBAND front end, get multiplied by a factor of 2 and you see them as 14 MHz signals.

The proof: listen in the 7 MHz band and check that here no signal is above S9+20.

If it is not receiver's overload, even a cold antenna joint could act as a diode and produce the same effect with very strong signals....Try with a different and smaller area antenna.

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Roger
Posts: 137
Joined: Fri Dec 29, 2017 7:59 pm

Re: Ghosts in the system

Postby Roger » Sat Sep 08, 2018 1:19 am

usasa wrote:Hi all!

It drives me crazy. I get it at night on 13.000 Mhz +, I get the 40 meter band (strong signals, lots of power) . I have a 100 foot 20 Ga. long wire antenna. The radio is in a copper lined case. I have SR (MHz) set to 5.0 and DEC set to 4. I have always used that setting for over a year now and I have just noticed the problem.
Any useful suggestions for improvement would be appreciated. I do love the radio. I have used SDR's before, the little dongles.

Thank you all!
Alex
USASA


Try using a lower sampling rate and no decimation. I suggest 2 MHz. sample rate and no decimation. You can also try Low IF instead of Zero IF.

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Paul
Posts: 243
Joined: Fri Feb 17, 2017 9:52 am

Re: Ghosts in the system

Postby Paul » Sat Sep 08, 2018 6:14 am

My starting knowledge base is pretty low!
However, can you expain how to achieve zero decimation please.
And on topic, could a high-pass filter help?

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usasa
Posts: 5
Joined: Fri Dec 30, 2016 7:00 am

Re: Ghosts in the system

Postby usasa » Sat Sep 08, 2018 6:46 am

Hi All:

Well I will try more different settings. It just drives me crazy, this has never been a problem before. Nothing has been changed to create this. Again thanks to all for the input. Happy monitoring!


Alex
USASA
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