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Post by Deleted on Jun 25, 2016 3:54:54 GMT
It's several years since installing the AMT5000 High-Efficiency AM transmitter from SSTran, and I'm doing a total check-out and re-tuning.
The range of this transmitter has remained the best of the house, good to about 1,000-feet and stronger toward the south because of the way the ground radials are laid.
Our AMT3000 is serving as the interim transmitter during the overhaul. It is resonant with a triangular loading coil grounded to the building I-beam, solidly serving our home campus.
Today was the first day of the upgrade, cleaning and checking the transmitter.
As days go by we will re-build the Wintenna (our antenna using a metal window frame) and improve the STL (studio-transmitter-linkage).
Full details will be typed out here.
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Post by Deleted on Jun 25, 2016 15:52:53 GMT
Audio Trick
At 10:10 AM this morning the AMT5000 was signed on the air in test mode for KDX Worldround Radio.
At this stage of refurbishment an audio upgrade was made which takes a little explaining.
One day while observing the modulation peaks of both AMT transmitters on the spectrum analyzer, I noticed that when the AMT3000 had a positive modulation swing the AMT5000 took a negative swing. I realized that somewhere in the audio chain out to the AMT5000 the polarity was inverted, and I quickly traced the cause.
The audio for the AMT5000 is taken from the Line Out of a Panasonic RE-7680 Stereo Tuner, and like many consumer audio products the polarity of the line output is inverted with regard to the input. To editorialize, I believe this is done intentionally, and I'll side-track to explain my "conspiracy theory".
The very sharpest sound from any audio chain is retained if the entire system maintains absolute polarity from input to output, and higher priced audio components are designed with this in mind. But the same manufacturers skimp on lower-priced products, which will not sound quite as sharp when compared to the "better" models.
The audio lines between the Panasonic tuner and the AMT5000 are un-balanced, which precludes the simple solution of flipping polarity possible with balanced (3-wire) audio lines.
My first thought was to insert an audio transformer which would fix the polarity situation but might be difficult to match at the higher impedances involved and would likely result in a drop in line level.
We paid a visit to the schematic diagram in the AMT5000 Manual and right there on the page was the perfect solution to the entire problem.
The standard input design for both the AMT3000 and AMT5000 transmitters is a stereo-pair of RCA jacks, anticipating that many users would be taking audio from a stereo source, and these inputs feed directly into a mixing circuit that combines L + R into a monaural signal for AM transmission.
The AMT5000 has a little publicized second input choice dubbed the "Professional Input" consisting of a differential input for balanced line.
We set to work combining both inputs to achieve our ends.
The stereo un-balanced signals from the FM Tuner enter the AMT5000's L + R mixer, which we isolated from its usual connection to the modulator, instead feeding the mixed signal into the differential amplifier.
So as to "flip" the audio polarity the positive mixed signal was input to the "-" input and the "+" input of the differential amp took its signal from the ground side.
Done!
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Post by Deleted on Jun 25, 2016 23:53:22 GMT
The RF Problem
Watching the AMT5000 carrier on the spectrum analyzer over a period of several hours, occasional "pops" were heard and this manifest on the screen as a 10 dB jump or drop in signal.
The antenna and ground system of the transmitter is several years old and was only a temporary installation to start out with, so I began by inspecting the ground side since it's exposed to a dirty environment.
Cleaning and reconnecting all joins in the ground system turned out to be the needed fix.
Now the AMT5000 is returned to full 100 mW service with proper audio polarity and it dominates the dial!
What comes next?
Two things lay ahead.
First, I want to install a first rate ground radial system below the floor for this particular AMT5000.
Second, it's time to build a tower 100-feet in the rear of the yard with complete ground radial system... the top-of-the-line type AM antenna... so finally the AMT5000 can be evaluated under the best circumstances.
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Post by Druid Hills Radio on Nov 28, 2017 20:25:51 GMT
The RF ProblemWatching the AMT5000 carrier on the spectrum analyzer over a period of several hours, occasional "pops" were heard and this manifest on the screen as a 10 dB jump or drop in signal. The antenna and ground system of the transmitter is several years old and was only a temporary installation to start out with, so I began by inspecting the ground side since it's exposed to a dirty environment. Cleaning and reconnecting all joins in the ground system turned out to be the needed fix. Now the AMT5000 is returned to full 100 mW service with proper audio polarity and it dominates the dial! What comes next? Two things lay ahead. First, I want to install a first rate ground radial system below the floor for this particular AMT5000. Second, it's time to build a tower 100-feet in the rear of the yard with complete ground radial system... the top-of-the-line type AM antenna... so finally the AMT5000 can be evaluated under the best circumstances. Carl: What became of your project? |
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Post by Deleted on Nov 28, 2017 21:32:46 GMT
Status of Projects
Seasons don't last long enough to get much done.
Over a year ago in 2016 we foresaw the following projects here at KDX:
First, we want to install a first rate ground radial system below the floor for the currently installed AMT5000 transmitter.
As of this time no action has been taken on the radials but the project is still on the to-do list;
Second, it's time to build a tower 100-feet in the rear of the yard with complete ground radial system... the top-of-the-line type AM antenna... so finally the AMT5000 can be evaluated under the best circumstances.
For clarity, we plan to build the 3-meter tower 100-feet behind the building, not erect a 100-foot tower. So far some yard clearing work has been done to prepare the site for construction. We can call this a slow-motion project-in-progress.
Remember our mantra: Slow But Better.
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Post by jimhenry2000 on Dec 1, 2017 3:55:12 GMT
The RF ProblemWatching the AMT5000 carrier on the spectrum analyzer over a period of several hours, occasional "pops" were heard and this manifest on the screen as a 10 dB jump or drop in signal. The antenna and ground system of the transmitter is several years old and was only a temporary installation to start out with, so I began by inspecting the ground side since it's exposed to a dirty environment. Cleaning and reconnecting all joins in the ground system turned out to be the needed fix. Now the AMT5000 is returned to full 100 mW service with proper audio polarity and it dominates the dial! What comes next? Two things lay ahead. First, I want to install a first rate ground radial system below the floor for this particular AMT5000. Second, it's time to build a tower 100-feet in the rear of the yard with complete ground radial system... the top-of-the-line type AM antenna... so finally the AMT5000 can be evaluated under the best circumstances. That reminds me. I need to get out there and inspect my radial system. I know I've had a couple chopped by my landscaper and need to check all the solder joints to the ground ring. |
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