Thanks all for your input! Upon KJ5HMX’s idea to try a narrowband receiver I was able to identify the interference at a 50ms period, not the 30ms of DMR’s TDMA. I can hear SWMH’s DMR independent of this.
With just 2m/70 equipment on hand, the strongest peaks in narrow FM are now 146.955 and 440.8625, so I strongly suspect the fundamental to be in the lower bands. Some of the strongest locations for receiving the signal aren’t even near any lights at all. Time to drag an HF receiver or SDR out here someday… From: BVARC <[email protected]> on behalf of John Denison via BVARC <[email protected]> Date: Wednesday, March 5, 2025 at 1:12 PM To: wb5itt <[email protected]>, John Denison via BVARC <[email protected]> Cc: John Denison <[email protected]> Subject: Re: [BVARC] Investigating QRM I thought that the old 145.47 repeater was now a digital repeater. 73 John Denison KD5YOU On 3/5/2025 1:00 PM, wb5itt wrote: Doubtful..a UHF signal won't cause harmonics in VHF. Probably noise from LED fixtures..they wipe out my mobile on VHF a lot of places...trying to hear my 146.94 in Vidor yesterday and I was in Orangefield maybe 10 miles away...stopped at a convenience store and their LEDs were so bad I could not go hear the repeater ...backed away and it was full scale again Chris WB5ITT Sent via my Samsung Galaxy S10e, an AT&T 5G Evolution capable smartphone..so there! 😂 -------- Original message -------- From: John Denison via BVARC <[email protected]><mailto:[email protected]> Date: 3/5/25 12:46 PM (GMT-06:00) To: [email protected]<mailto:[email protected]> Cc: John Denison <[email protected]><mailto:[email protected]> Subject: Re: [BVARC] Investigating QRM Maybe you are receiving interference from a DMR repeater at the SW Memorial Hospital? 73 John Denison KD5YOU On 3/3/2025 5:03 PM, baaelectronics via BVARC wrote: Hi all, lately I've been having some interference come up when trying to join in on the Stir-Crazy nets when I am portable during the week. Around the HCU campus between 12:00 and 13:50, I notice the same four narrow peaks of S9 splattering noise - not quite harmonics of 60Hz but not just static either. It reminds me of what DMR sounds like on an FM receiver. They are strongest on 146.915, 146.935, 146.955, and 146.995MHz. 146.94MHz is noisy but sometimes copyable. My rudimentary understanding of RF harmonics led me to check 440.86, but nothing was heard there. Any advice for someone who just has an HF radio and dual-band HT to investigate more? I take the antenna off my IC-W32 and it all goes away (including receiving 146.94 too), so DF’ing that way (unless I find the fundamental) is out of the question. A thought was to have a classmate use an RTL-SDR to scan outside amateur bands to see if there are harmonics elsewhere, but I have yet to do that. [A person in a suit smiling Description automatically generated] Blake Alley | BAA Electronics QRZ: N5BAA Mobile: (281) 450-5785 [email protected]<mailto:[email protected]> [A blue circle with white letters on it Description automatically generated]<https://www.linkedin.com/in/baaelectronics/> [A red and white play button Description automatically generated] <https://www.youtube.com/@baaelectronics> [A blue circle with a white v in the middle Description automatically generated] <https://vimeo.com/baaelectronics> [A logo of a camera Description automatically generated] <https://www.instagram.com/baaelectronicsyt/> ________________________________________________ Brazos Valley Amateur Radio Club BVARC mailing list [email protected]<mailto:[email protected]> http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org Publicly available archives are available here: https://www.mail-archive.com/[email protected]/
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