Yesterday at turn-on time I noticed a frying sound on the carrier of the AMT5000. It was intermittent, sounding like short digital bursts at very irregular intervals.
Right away the back-up AMT3000 with loading-coil and advanced antenna took over the day's schedule.
Naturally the first thought was trouble in the transmitter, maybe a bad solder or aging capacitor. But with the carrier off, I noticed that static on my frequency sounded similar to the frying sound heard on the carrier.
The culprit was the strong buzz at 1700kHz, the 2nd-harmonic frequency of 5kW 850kHz, whose tower a mile away can actually be seen from the roof. That buzz was much louder than usual and was spilling over all the way to 1680kHz.
In a previous post member Rich responded to the "2nd-harmonic" that I described, telling that it most likely was not actually the station's harmonic, but was an artifact produced by radio receivers reacting to the very strong 850kHz signal.
Proof came last night when 850kHz signed off to open the frequency for KOA in Denver, and the AMT5000 carrier became perfectly clean.
Today the AMT5000 is proudly back in service.
...it most likely was not actually the station's harmonic, but was an artifact produced by radio receivers reacting to the very strong 850kHz signal. ...
Such harmonics can be produced by any non-linear circuit, including the output stage of a transmitter -- where they could be radiated along with the desired signal.
Even two random conductors not well bonded together can act as a (poor) diode that will produce and radiate harmonics of a very strong EM wave.
That means it may, but maybe not, coming from the 5kW AM station a mile away, or... I don't know how many possible sources there actually are for the 1700kHz buzz, given Rich's further comment.
One thing we know... it's not my transmitter causing the issue.
Every solution is a new problem. -C. Blare 2014
One thing we know... it's not my transmitter causing the issue.
It would take a fairly thorough set of measurements to determine that, Carl.
One simple test would be to install a trap tuned to reject 850 kHz (only) at the output of your transmitter. It might reduce the amount of 850 kHz energy present in the output stage of your transmitter so that any 1700 kHz component it generates will be insignificant.
But even that may not work if the 850 kHz is entering the transmitter by other conductors, and/or inadequate shielding.
While my transmitter is turned off, there continues to be a loud buzz at 1700kHz on all radios for miles around, with detectable distorted modulation matching the program on 850kHz.
While turned off, is my transmitter thus "ruled out" as a cause of the "harmonic?"
... if the 1700 kHz signal appears in receivers for miles around KFUO's tower.
If the interference was just due to the second harmonic then the audio would sound normal. The buzz could be coming from the station's signal mixing in a nonlinearity in the power lines or system (as Rich mentioned) and that would account for the buzz. If this is the case, the station could be doing nothing out of specification and probably has no control over this.
There once was a complaint from a neighbor who heard my ham radio signal via his TV and I traced the problem to a loose and corroded connection at an amplifier mounted on his TV antenna mast. It was an easy fix but often such bad connections are not found, especially if they are in the power grid.
Neil
Very informative, gentlemen, and since this buzz-plus-supressed audio at 1700 is heard everywhere in a several mile range... I have never tried to drive beyond it... only driven about 3-miles in a circular area... the corroded grid or fence or flagpole that is causing the RF image might not be traceable by myself alone.
They have a very old tower... maybe that's the source. They have a chain-link fence around the tower. Maybe that's the source. Somebody has an old wash-machine in their garage.. maybe that's the source. The power-pole ground wires I've seen up and down the street look old and worn. Maybe...
WDCF AM 1350 wrapped a STL antenna isolator used on thier tower once with a black plastic bag to keep water out of it. Problem was that the bag has a carbon component to it. So....the bag caught fire, burned up the isolator and knock the sister station WZHR into a dead air mode. The owner was so cheap that he would keep tuning on an old Gates 1000 with a cue stick rather than spend the 75 bucks for the thermal power-on relay tube.
For several years I, Carl Blare, have talked up the planned outdoor antenna installation based on PhilB's "Ultimate Antenna" description found elsewhere on this website.
Roadblocks to progress have included a major stack of old bamboo poles and the polar vortex.
But things are getting close, as the poles are almost all removed and the vortex has thawed.
Another step-forward are the radial clips received from Ross Radio which will allow easy-no-fuss on-the-ground installation of the radial wires.
Quite soon an order will be placed with sstran.com for an AMT5000-X, which I think is the proper label for the transmitter with outdoor enclosure.
It's almost time to call the Dig-Right-Crew to make sure I can sink a ground rod in the spot, about 100' behind the Internet Building.
As yet unsolved is just how I will run power and audio wires back to the site, but I will definitely call on members here for ideas once that gets started.
Get ready to rumble.
woohoo!!!!
(while dancing the cabbage-patch) - "go carl... go carl.."
Don't hurt the cabbage! I love cabbage. The one I have now in the refrigerator would look good on my pillow where I could talk to it while drifting away.