An AM nearly 2khz off frequency?

[Mediafrog+]

I'm too lazy to look up the license, but that would likely mean that the antenna is a tiny bit over 1/2 wave.

FCCData.org has the WHAS electrical height as 201.1 degrees.

 

[KeithE4]

How would any Ancient Modulation transmitter be able to be off frequency by 2 kHz in the first place? What are they using as their carrier oscillator? Even an old-fashioned crystal would be more stable than that. Adding a PLL would make it even more stable. If it were synthesized, I would think it would be rock-stable unless something in the programming went south.

I don't know what broadcast transmitters use these days for frequency control, but every transmit oscillator in my house is synthesized, and that's just on the ham bands, with a whole lot less frequency tolerance requirements (as long as we stay inside our bands). I would think that a 20 Hz tolerance would be fairly trivial nowadays.

 

[nitroengine]

It's not uncommon to see an AM station operating off-frequency. Get an SDR or load a public KiwiSDR, zoom all the way in on the waterfall spectrum and jump around the dial. You'll see many who aren't right on center, and many who are even beyond the ±20Hz FCC limit. Especially on the crowded "Graveyard channels". Stations running greater than ±100Hz off-frequency are seen a number of times per year. Those offset carriers become easy targets for DXers. Usually, those get fixed in the matter of days to a week or so. Sometimes it's the backup transmitter that is off-frequency, so a reported carrier offset may disappear for months or longer, then suddenly reappear for a night or two. 1130 KTLK's (Minneapolis, MN) backup transmitter has an offset of about -77Hz, been that way for years.

There's a list of these offsets that you can search, with dates showing when they were last measured.

Frequency offsets from MWLIST - AMLIST - TBL

www.mwlist.org

1260 WNDE (Indianapolis, IN) has been running with an offset of +35Hz for number of years now. They cause a serious low rumble here at night, and they are often strong enough that you'll hear garbled distorted audio, either from WNDE, or from a weaker on-frequency station.

1070 used to be almost unusable here at night. 1070 KFTI (Wichita, KS) was at -24Hz and 1070 KSKK (Verndale, MN) was +62Hz. Those made hearing KNX out of Los Angeles especially tough. Fortuantely, KSKK appears to have fixed their transmitter within the past several months. KFTI has been off the air due to damage to their tower site by theifs.

Local listeners close enough to the off-frequency station really wouldn't notice. Manually tuned radios can easilly be bumped to the right position, and the PLL in digitally tuned radios shouldn't have a problem locking to a carrier that is a few hundred Hz off. It's when night falls and other stations who are closer to being on-freqency start to come in. Those will cause low rumbles and distortion, especially for listeners who are on the outer parts of the listening area.

 

[kevtronics]

AM IBOC (HD Radio) stations should be exactly on-frequency, since their exciters use NIST's atomic clock as a reference. That was one of iBiquity's claims of how IBOC would improve analog reception, that if all AM stations were using IBOC, co-channel beats would be eliminated.

 

[secondchoice]

AM IBOC (HD Radio) stations should be exactly on-frequency, since their exciters use NIST's atomic clock as a reference. That was one of iBiquity's claims of how IBOC would improve analog reception, that if all AM stations were using IBOC, co-channel beats would be eliminated.

Had all the AM stations gone IBOC AND the car receivers had had a sub one dollar license fee and IBOC was required ON ALL AM receivers, AM might have some life left in it. But would have, could have, should have, didn't stop the listener ship from sailing leaving AM behind.

 

[secondchoice]

But a mis-tuned antenna just raises the SWR. That does not affect the frequency: that is an effect of the transmitter
.

I personally have never been around an AM transmitter that far off frequently. I still still believe the antenna current readings would be way off.

One could wonder if they have some kind of "non FCC approved" transmitter that does the 9 khz channels they bought (cheap) for nighttime service and tried to "modify it' or using Ham equipment?

IMHO there is a lot of questionable equipment on various websites that would generate fines from the FCC.

 

[davideduardo]

I personally have never been around an AM transmitter that far off frequently. I still still believe the antenna current readings would be way off.

A couple of times I ran several of my AM stations on a "split" frequency. For example, 570 kHz HCRM1 in Quito would move for a few hours on a Monday morning to 565 kHz, using a different crystal. There was no difference in any of the readings on the transmitter or in the ATU.

One could wonder if they have some kind of "non FCC approved" transmitter that does the 9 khz channels they bought (cheap) for nighttime service and tried to "modify it' or using Ham equipment?

Any frequency agile transmitter will be able to select the desired channel.

IMHO there is a lot of questionable equipment on various websites that would generate fines from the FCC.

Yet those transmitters, made outside the U.S., are common in much of the rest of the world where AM still is alive. We DXers don't see "off frequency" stations anywhere nearly as often as was common in the 60's and 70's. That makes me suspect that some kind of catastrophic failure of a circuit is causing the frequency variations, not gear that was defective to begin with.

 

[secondchoice]

A couple of times I ran several of my AM stations on a "split" frequency. For example, 570 kHz HCRM1 in Quito would move for a few hours on a Monday morning to 565 kHz, using a different crystal. There was no difference in any of the readings on the transmitter or in the ATU.

Any frequency agile transmitter will be able to select the desired channel.

Yet those transmitters, made outside the U.S., are common in much of the rest of the world where AM still is alive. We DXers don't see "off frequency" stations anywhere nearly as often as was common in the 60's and 70's. That makes me suspect that some kind of catastrophic failure of a circuit is causing the frequency variations, not gear that was defective to begin with.

Back to America.. IIRC there is a kit you have to buy to change a Nautel J1000 AM* transmitter frequency. Compared to the old MW1 it was at least 50 times better and 40 years younger.

You do learn something every day. That dual crystal rig swapping frequencies. Was it a tube rig? If so did you have to turn off the "filaments" to swap frequency?

I have seen two day rain screw up antenna current readings. The station tower site soil was super bad (around 90%clay almost as hard as asphalt) and the insulator at the tower base had some cracks too. They were going to use a grounded tower "soon" after I left.
*Last AM transmitter I touched a couple of decades ago.