What's the farthest from a radio tower you heard "mirroring signals" or harmonics of a FM/AM station?

[Xale57]

I've always thought it was cool/interesting to listen to a mix of stations on different frequencies. My own personal harmonic distance was 16 miles on FM. From my Grandmas home in Glastonbury, CT, I used to hear a harmonic of 92.5 WWYZ and 93.7 WZMX on the 94.9 frequency. This was 2010/2011 using a Tecsun PL-310 and my Insignia NS-HD01 portable HD radio I got in 2009 (great radio for FM DX but super sensitive to multipath, later models eliminated the multipath)

Back home in New Jersey, I get harmonics of all the meadowlands stations that are 3-6 miles away and the Clifton NJ AM's 930 and 1430, 2 miles away. WABC is 6 miles away and my Tecsun PL 660 on DX mode picks up harmonics on 860,870, and 1540.

What is the furthest harmonic or mirroring signal you've heard on FM and AM? Curious especially in less crowded and better conductive markets outside the North East US!

 

[KeithE4]

I've always thought it was cool/interesting to listen to a mix of stations on different frequencies. My own personal harmonic distance was 16 miles on FM. From my Grandmas home in Glastonbury, CT, I used to hear a harmonic of 92.5 WWYZ and 93.7 WZMX on the 94.9 frequency. This was 2010/2011 using a Tecsun PL-310 and my Insignia NS-HD01 portable HD radio I got in 2009 (great radio for FM DX but super sensitive to multipath, later models eliminated the multipath)

That's not harmonics. That's intermod. Intermod is generated in your receiver, not transmitted over the air. The 94.9 signal is called "Third Order," which is the difference between twice one frequency minus the other: (93.7 * 2) - 92.5 = 94.9. The problem is poor design of your radio.

Back home in New Jersey, I get harmonics of all the meadowlands stations that are 3-6 miles away and the Clifton NJ AM's 930 and 1430, 2 miles away. WABC is 6 miles away and my Tecsun PL 660 on DX mode picks up harmonics on 860,870, and 1540.

Probably not harmonics. True harmonics generated by the transmitter on either band are rare, as well as a violation of FCC rules. It's probably a combination of intermod and a poor front end that overloads easily. 1540 is the 2nd harmonic of 770 (WABC), but I highly doubt it's coming from the transmitter.

What is the furthest harmonic or mirroring signal you've heard on FM and AM? Curious especially in less crowded and better conductive markets outside the North East US!

Once, back in the '80s, I did hear the 3rd harmonic of a poor quality Ancient Modulation transmitter that was being used at a drive-in theater (i.e. a Part 15 device) that spewed its garbage into the 160 and 80 meter ham bands. I was far enough away, about 10 miles with a weak signal, where I knew that it wasn't intermod products being generated in my ham rig. It was eventually fixed. I don't remember ever hearing harmonics of a legit transmitter on any frequency.

 

[gr8oldies]

I've caught WLW on 1400 but that was almost within visual range of the transmitter.

 

[SomeRadioGuy]

KCGY 95.1 and KUWR 91.9 both 100kw blasters on tall towers next to each other up on a big ass hill, mix all over laramie on 98.3.. hear them both at the same time and garbled RDS

KHAT 1210 would put out spurs in a few different places on the dial.. could hear 1370 all over town

 

[KeithE4]

I've caught WLW on 1400 but that was almost within visual range of the transmitter.

I lived within a mile of then-WMAQ in the late '70s, but never heard harmonics on 1340.

But when I lived in Bloomington IN in the late '60s, WFIU/103.7 ran 75kW on a short tower in the middle of the Indiana University campus, about 2 miles from my house. They overloaded probably every FM radio in the central part of the city. When they cut their power in half and moved to the 500 foot WTIU/30 tower on the south side of the city in 1970, that went away (at least for us). Even my cheap shortwave radio picked them up every couple of MHz. All due to poor receiver design.

 

[kevtronics]

AM receivers are prone to picking up an image of a signal at twice the IF away from it. For example most digital tuners (except for car radios) use an AM IF of 450 kHz, so you can sometimes pick up an image 900 kHz above or below the station's actual broadcast frequency, if the signal is very strong.

I have a Part 15 AM transmitter operating on 1620 kHz, and a 1980s digital tuner that only goes up to 1610. But if I tune it to 720 kHz (1620 - 900), I can pick up the signal if I'm within close range of the transmitter.

As noted above, the transmitter isn't actually putting out this +/-900 kHz image; it's purely a receiver-induced phenomenon.

 

[Xale57]

That's not harmonics. That's intermod. Intermod is generated in your receiver, not transmitted over the air. The 94.9 signal is called "Third Order," which is the difference between twice one frequency minus the other: (93.7 * 2) - 92.5 = 94.9. The problem is poor design of your radio.

Probably not harmonics. True harmonics generated by the transmitter on either band are rare, as well as a violation of FCC rules. It's probably a combination of intermod and a poor front end that overloads easily. 1540 is the 2nd harmonic of 770 (WABC), but I highly doubt it's coming from the transmitter.

Once, back in the '80s, I did hear the 3rd harmonic of a poor quality Ancient Modulation transmitter that was being used at a drive-in theater (i.e. a Part 15 device) that spewed its garbage into the 160 and 80 meter ham bands. I was far enough away, about 10 miles with a weak signal, where I knew that it wasn't intermod products being generated in my ham rig. It was eventually fixed. I don't remember ever hearing harmonics of a legit transmitter on any frequency.

I've heard of a similar phenomenon in the Connecticut Board years ago. It didn't do that with other frequencies. Ex. Hearing WDRC and WMRQ on 105.3

 

[crainbebo]

I have heard KIOK Pasco bleed all the way to 95.3, 104 miles from the transmitter line-of-sight at approximately 6,500 feet, along the ridge trail that takes you to Burnt Mountain, which is about 5 mi above Rimrock Lake and 10 mi from White Pass.
When KFFM-107.3 ran spurs at 106.5 and 107.9 for several months, around 2017-18, I heard the 107.9 spur up in Ellensburg (30 mi from the transmitter).

 

[Schroedingers Cat]

I've heard RITOIE on AM radios, sometimes from two strong AM signals transmitting from a half mile apart. Other times when I had a preamp and it caused the receiver to have this. Probably caused by second harmonics caused by the preamp.

Other situations where an AM and FM were at the same site, and the sum and difference was the AM signal causing a spur either side of the FM, after they collocated the AM and FM at the same new site. Seriously, it was once WHGR 1290 (yes, HGR1290) 1.29 MHz either side of WUPS 98.5. WUGN 99.7 noticed it interfering with their signal near Houghton Lake. Clear Channel later bought it to put it off the air, to upgrade WOOD 1300. Later DA proofs and radial conductivity measurements for the new WOOD facility and WCCW 1310 showed that this was probably unnecessary, if the new WOOD site radial conductivities had been investigated.

 

[Xale57]

I have heard KIOK Pasco bleed all the way to 95.3, 104 miles from the transmitter line-of-sight at approximately 6,500 feet, along the ridge trail that takes you to Burnt Mountain, which is about 5 mi above Rimrock Lake and 10 mi from White Pass.
When KFFM-107.3 ran spurs at 106.5 and 107.9 for several months, around 2017-18, I heard the 107.9 spur up in Ellensburg (30 mi from the transmitter).

104 miles!!! That's pretty cool. Here in the Northeast, you can't even receive stations that are half the distance!

 

[Steve Green NEPA]

Merely some harmonix stories here ; nothing special -- with one puzzler.
A basement apartment in NE Philly where I stayed for a few years was maybe 5 miles from the tower, across the Delaware in NJ, of Philly's 1210 WCAU. I was making my own dials (nose in the air) for better frequency determination on a Lafayette HA 600a. And in decreasing signal strengths, like half-lives, WCAU harmonics on 2420 kHz, 4840, 9680 plus a few other spots in between (maybe 3630, 6050, 7260 iIrc? ) made for nice, general references on the new dials *
A car radio drive one afternoon past WABC's 770 stick in Lodi NJ and a random whim of a tune brought in them on 1540. That would be their first harmonic, right? Not their second? It was pretty weak, though. Didn't carry far.
A Long Island drive one day past the Islip Speedway, home to the tower ** of 540 WLIX, brought them doing their dutifully-enfeebling echoes on 1080 and 1620 as well. But as in WABC's case, not much distance was involved.
The 'puzzler' I mentioned remains so to this day, even with the station having gone dark and burned down (in that order) over a decade ago. WGLI 1290 from the South Shore COL of Babylon had an incredibly clumsy 3-tower directional shoehorn of a signal that sent a small back lobe northwest ; nothing to the SW or NE, and maybe 4990 of its 5000 watts toward Bermuda. Buddy says the station got callers from Pembroke. But on every single radio available .... car radios, transistors, communications rigs, Zenith 500 portables .....WGLI came in, weaker of course, on a hair above 1160 kHz -- night and day. Even odd-er was that the 1160 signal seemed to have the exact same directional characteristics as the parent 1290 one! Logic mandates that the 1160 wave had to've emanated from the radio station itself, not the fault of the receivers. But we couldn't figure that one out. Long Island had only one other AMer operating at night (1240 WGBB) but the signals of the two stations hardly overlapped -- and certainly couldn't mix or clot in WGLI's back lobe. WGBB didn't reach up there.

* The 910 IF shrills from another radio provided a few pinpoints on the AM dial, too.
** 540 WLIX Islip was 250 watts omni and daytime back then. Wow did they get OUT, though!

 

[Rusty Muck]

I've caught WLW on 1400 but that was almost within visual range of the transmitter.

Same with 850 WKNR on 1700 at their North Royalton transmitter.

 

[Schroedingers Cat]

Has anyone taken an FIM-41 to those areas to check if those harmonics are radiated or receiver induced? Both are harmonics, the source is the issue.

I've also heard WSGW 790 on 1580 in their large minor lobe along I-75, fairly close to the transmitter.

 

[PTBoardOp93]

By regulation (73.44(b)), the AM broadcast facility must knock down all frequencies at least 75kHz away from the carrier (including all harmonics) by at least 80dB.

80 dB is a lot. In sound pressure, it's the difference between a normal conversation with your spouse, and operating a chain saw.
In broadcast terms, 80 dB is roughly than the difference between a 50kW AM station, and a part 15 compliant AM transmitter.

80 dB isn't so huge that it would be impossible to receive, and it is possible that some broadcasts have been made with non-compliant equipment, so the thread is a valid subject. I just wanted to add a bit to Keith's excellent post above.

 

[SomeRadioGuy]

By regulation (73.44(b)), the AM broadcast facility must knock down all frequencies at least 75kHz away from the carrier (including all harmonics) by at least 80dB.

80 dB is a lot. In sound pressure, it's the difference between a normal conversation with your spouse, and operating a chain saw.
In broadcast terms, 80 dB is roughly than the difference between a 50kW AM station, and a part 15 compliant AM transmitter.

80 dB isn't so huge that it would be impossible to receive, and it is possible that some broadcasts have been made with non-compliant equipment, so the thread is a valid subject. I just wanted to add a bit to Keith's excellent post above.

Nothing was ever done in in the case i mentioned above

KHAT 1210 and non co owned KOWB 1290 are about 1/4 to 1/2 mile apart, neither has filters for each other.... KHAT filed to become a daytimer.. but hasnt pulled the night p[lug yet

Townsquare seems to wanna forget they own KOWB..... took 3 weeks after a flood from a burst pipe to get the AM back on.

 

[cc333]

On the radio in our 2014 Toyota Prius v, I've noticed that KCBS 740 will come in on 1480 (2*740), but only in the daytime. At night, it's usually a mix of KEJB and KVNR, and maybe some faint whispers of KYOS in the background before they drop to night power.

I haven't noticed this on any other radio in any other car anywhere I've tried listening.

c

 

[MarioMania]

When I move back to Carmichael, CA next week

I will have 2 FM transmitters in 15 min walk, So I will get FM overload on cheap radios

 

[schmave]

In Columbus, I used to hear 1460 WBNS regularly down around 540 on my home radio. This was in the 90s when I was a teenager. I lived about six miles from their towers at the time.
Their sidebands at my grandparents' home, less than two miles from the towers and within sight of the beacons, would bury everything from 1430 to 1500 during the day. Less so at night, especially given that they lived to the east, where WBNS throws a null.

 

[Schroedingers Cat]

In Columbus, I used to hear 1460 WBNS regularly down around 540 on my home radio. This was in the 90s when I was a teenager. I lived about six miles from their towers at the time.
Their sidebands at my grandparents' home, less than two miles from the towers and within sight of the beacons, would bury everything from 1430 to 1500 during the day. Less so at night, especially given that they lived to the east, where WBNS throws a null.

For a radio with a 455 kHz IF, it would be on 550 kHz.

Based on former minimum efficiency standards, WBNS with it's 202.5 degree Blaw Knox tower would be greater than the equivalent of 10000 watts nondirectional Days.

Before NRSC standards, AM stations had a wide frequency footprint .

They moved from 1430 to 1460 in 1941.

Back in the late 1930s, they went directional with very shallow nulls, with 1 kW Night. Previously, they were 500 watts Night, nondirectional.

https://licensing.fcc.gov/cgi-bin/prod/cdbs/forms/prod/getimportletter_exh.cgi?import_letter_id=50822

 

[schmave]

550 sounds right as well. I just knew it was low on the dial. Such a harmonic would have no problem overpowering WKRC at my location.