Interesting phenomena or has something changed?
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I've noticed in the last few weeks that my server (KA1GJU @ PCARC) is getting QRM from a nearby 5KW AM BC station on 1540 kHz 5.2mile (8.4km) miles away. This installation was relatively QRM free until recently. I've noticed this station creeping in all over the bands, and it's not just the Airspy, it's also on the SDR-iq. The antenna is an EFW of ~200' long, with a 9:1 unun, grounded at the unun and long length of 1/2" 75 ohm CATV hardline to shack.
Right now, at 1311z it's slowly fading in and out on 14230 kHz (9.24 harmonic of 1540kHz?). There is some SSTV under it giving false S-meter readings, but the waterfall shows the slow fades, images are ~ one minute apart. Slow QSO is normal for this time of day since the Sun rose up just over an hour ago. Do you think the issue is on my end with something in the antenna/feedline or does the AM BC station have issues? Open ground connection perhaps? I would have to trudge out in snow shoes to check the antenna, recent storm dumped on us few days ago. 73 Kriss KA1GJU
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N8CVW
just a knee jerk advice ... maybe listen with a low sensitivity wide band antenna, eg youloop, maybe short a whip, straight into the receiver, no preamp, nothing to IMD to find out what actual signal is present from what (little) i know the culprit could be corrosion acting like a diode Paul N8CVW
On Feb 5, 2021, at 8:36 AM, Kriss Kliegle KA1GJU <kliegle@...> wrote:
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That brings back memories of the early 60s when we were operating G3OUL in the Students Union at Liverpool University. We kept breaking through into the Tannoy system. It turned out to be diode-like corrosion in the lead roof of the building if my memory serves me right. Allan G3PIY
From:
main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of N8CVW
just a knee jerk advice ...
maybe listen with a low sensitivity wide band antenna, eg youloop, maybe short a whip, straight into the receiver, no preamp, nothing to IMD
to find out what actual signal is present
from what (little) i know the culprit could be corrosion acting like a diode
Paul N8CVW
On Feb 5, 2021, at 8:36
AM, Kriss Kliegle KA1GJU <kliegle@...> wrote:
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Been so long since I installed that antenna setup, I don't remember if I used ring terminals (ugh) on the antenna feed point onto the stainless steel Unun connections or just wrapped the copper wire and tightened the nut. Same for the ground connection.
We have a VE test session there tomorrow, guess I better bring snow shoes, emery cloth, wrench and some Scotch 33+. If the WiFi will reach that far out into the woods, I can watch in real time to see where the issue is. 73 Kriss KA1GJU
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Upon further searching, it's all over the 2Mhz band, strong and clear! 🤬
73 Kriss KA1GJU
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Paul Cianciolo
Kriss
Simple way to find out of this is generated by the RX or external to the RX is to simple put a 10 dB pad in front of the RF. A real 10db pad that is external to the radio. If the signal is generated outside the RX all the images will drop by 10 dB, if they drop by more… problem is in the RX.
FCC says that spurious emissions need to be -80 to 84 dB down from the mail carrier. Looks like you might be in the very high signal area. What is the S meter reading of the station.
I run into this problem quite often at work where a Ham lives close to a AM broadcast station, and sees the 2nd or third harmonic on 160 or 80 meters. Going so far as to lodge a compliant with the FCC sometimes. Consider a Large signal, such in my case 610 Khz 1 KW at 1.4 Miles, and a large antenna, I can see +70 db on the S meter. Add to that -80 Dbc FCC spec from the station.. and that still leaves a legal S7 or so signal level.
I am not saying this is your case, I just add it for general information. From the look of your spectrogram it appears you have something else going on there.
How strong is the 1540 Khz from WXEX? Is it.. at your house.
Good luck with the RFI
PaulC W1VLF
Check out my Youtube Channel W1VLF
From: main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of Kriss Kliegle KA1GJU
Upon further searching, it's all over the 2Mhz band, strong and clear! 🤬
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Hello Paul,
The readings for WXEX, AM 1540 of Exeter, NH are as follows: At the PCARC (KA1GJU @ PCARC server) site, S9+64dB or -10.1dBm via an SDR-iq with ONLY +12dB IF gain and 0 RF Gain (which approximates similar S-meter readings to my 'rice box' radios. At my home QTH (Super Station #1) with similar antenna, S9+55 or -19.5 dBM and same gain settings as above. On my Super Station #2, with yet another similar antenna but has your AM BC filter installed, I get S9+37 or -36.7dBm Both PCARC and my QTH are 5.2 and 5.1 miles respectively from the 5KW station. It seems on both SDR's (Airspy discovery and SDR-iq) at the PCARC site WXEX is very strong and numerous images of it appear throughout the upper bands. None of which are viewable/audible on my QTH servers. I'm guessing there's some corrosion on the connections out there somewhere, as previously mentioned by N8CVW. 73 Kriss KA1GJU
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Siegfried Jackstien
a very strong signal "modulates" your 0hz spot ... it is NOT on 14.230 (never heard of a 9.24 harmonic ... grin) if you tune your 20m receiver higher ... say to 14.350 or 14.500... and set your receiver window again at centre (the 0hz spot) you sure will also hear it i am guessing that you maybe find it "anywhere" on shortwave but in all cases at the damned 0hz area .... ok ... on REAL harmnics (4620 as an example) it will be much
stronger ... but i clearly see that your "9.24" harmonics is not
harmonics receiving but using an sdr on 0hz if greetz sigi dg9bfc Am 05.02.2021 um 13:36 schrieb Kriss
Kliegle KA1GJU:
I've noticed in the last few weeks that my server (KA1GJU @ PCARC) is getting QRM from a nearby 5KW AM BC station on 1540 kHz 5.2mile (8.4km) miles away. This installation was relatively QRM free until recently. I've noticed this station creeping in all over the bands, and it's not just the Airspy, it's also on the SDR-iq. The antenna is an EFW of ~200' long, with a 9:1 unun, grounded at the unun and long length of 1/2" 75 ohm CATV hardline to shack.
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n2msqrp
Kriss,
Can you test with different antenna and see if the problem is still present?
Mike N2MS
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On Fri, Feb 5, 2021 at 08:19 PM, n2msqrp wrote:
Just came back from clubhouse for the VE test session and did some tests afterwards. It appears the QRM is on the 160M inverted vee as well. If I take the club's IC-7300, I can hear/see the same garbage as I do on the two SDR's on the +200' EFW and the 160M vee. If I go to the 80/40m fan dipole it's still there, but very attenuated. On the 40M dipole, it's nonexistent. So the signals are really there, but why not at my house which is the same distance? If the AM 1540 tower is a single tower, would it not be omni-directional? Currently it's after sunset, and their output power is 5 watts so no further testing until AM. Currently, at 1815 local, WTSN, a 5KW station (24/7) on 1270AM is also appearing very strong on 2540 at -67dBm, first harmonic at a distance of 10.8 miles away. Also on the second harmonic of 3810 kHz at -77dBm. 73 Kriss KA1GJU Looks like an AM BC filter to be built and installed soon. I have to go to TX for 6 days, so after that I will have to break out the soldering iron. 73 Kriss KA1GJU
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jdow
Nearby fence with corroded wire? Tower bolts that
are rusting out? Basically it sounds like you have an antenna site
that has a diode junction with an antenna on it nearby.
toggle quoted messageShow quoted text
{^_^}
On 20210206 15:25:50, Kriss Kliegle
KA1GJU wrote:
On Fri, Feb 5, 2021 at 08:19 PM, n2msqrp wrote:
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I concur with Joanne We used to run into this when I did interference mitigation for Department of Communications. Strong signals, corroded metal joints= problems. 73 Brent Sent from my Galaxy
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I once had QRM from a 5Kw AM broadcaster about 1/3 mile across a river, caused by arcing in their nominally gas insulated coax. They were down for some weeks until that could be replaced.
Cortland
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I thought perhaps both SDR's at the site were fried with RF possibly, so I added another Airspy HF+ Discovery to the mix. Same problem on that one too. AM stations showing up on harmonics and in between their harmonics (fractions thereof). Going to be snowing this weekend, so I will put together another AM BC filter of Paul's, W1VLF, design.
WEXE operates on 1540 kHz, but appears on **1810kHz , **2470kHz, **2810kHz, and the 1st harmonic of 3080kHz. ** mixing with another AM BC station 73 Kriss KA1GJU
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Simon Brown
Could be intermod on an antenna connection somewhere, dissimilar metals…
Simon Brown, G4ELI
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Kriss Kliegle KA1GJU
Sent: 13 February 2021 12:16 To: main@SDR-Radio.groups.io Subject: Re: [SDR-Radio] Interesting phenomena or has something changed?
I thought perhaps both SDR's at the site were fried with RF possibly, so I added another Airspy HF+ Discovery to the mix. Same problem on that one too. AM stations showing up on harmonics and in between their harmonics (fractions thereof). Going to be snowing this weekend, so I will put together another AM BC filter of Paul's, W1VLF, design. -- - + - + -
Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.
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Simon Brown
toggle quoted messageShow quoted text
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Kriss Kliegle KA1GJU
Sent: 13 February 2021 12:16 To: main@SDR-Radio.groups.io Subject: Re: [SDR-Radio] Interesting phenomena or has something changed?
I thought perhaps both SDR's at the site were fried with RF possibly, so I added another Airspy HF+ Discovery to the mix. Same problem on that one too. AM stations showing up on harmonics and in between their harmonics (fractions thereof). Going to be snowing this weekend, so I will put together another AM BC filter of Paul's, W1VLF, design. -- - + - + -
Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.
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jdow
That will work as long as the IMD is not being
generated in corroded fence wiring or the like.
toggle quoted messageShow quoted text
{^_^}
On 20210213 04:15:42, Kriss Kliegle
KA1GJU wrote:
I thought perhaps both SDR's at the site were fried with RF possibly, so I added another Airspy HF+ Discovery to the mix. Same problem on that one too. AM stations showing up on harmonics and in between their harmonics (fractions thereof). Going to be snowing this weekend, so I will put together another AM BC filter of Paul's, W1VLF, design.
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Simon Brown
7:57am #61435
What’s your antenna splitter design?
Simon Brown, G4ELI
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I had a problem with overload and garbage on my RSP2 from our local station on 800 khz. A simple series tuned LC circuit with a 365 pf variable and a ferrite toroid coil solved the problem. I just connected it across the receiver input with a BNC tee. If it's being generated internally, it will help. If it's external..ie dissimilar metals, corrosion, etc., it will still be there. good luck Brent VE3CUS Sent from my Galaxy
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Simon Brown
My gut feeling is that an unintentional mixer is inline, this being a connection between antenna, feeder …
Simon Brown, G4ELI
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Brent Seres/ VE3CUS
Sent: 13 February 2021 14:30 To: main@SDR-Radio.groups.io Subject: Re: [SDR-Radio] Interesting phenomena or has something changed?
I had a problem with overload and garbage on my RSP2 from our local station on 800 khz. A simple series tuned LC circuit with a 365 pf variable and a ferrite toroid coil solved the problem. I just connected it across the receiver input with a BNC tee. If it's being generated internally, it will help. If it's external..ie dissimilar metals, corrosion, etc., it will still be there.
good luck Brent VE3CUS
Sent from my Galaxy
-- - + - + -
Please use https://forum.sdr-radio.com:4499/ when posting questions or problems.
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