- November 22, 2018 at 11:44 am #107455
There was a time when this forum cooked and steamed with tech talk about new transmitters, antenna designs and methods for applying the Part 15 Rules. Why has that died down?
My guess is that the folks posting these days have fully developed operating stations with the technical snags all solved and nothing further to ask about.
I mentioned elsewhere that I plan further technical explorations in the future which means some tech talk will return, so maybe I should start right away with something small.
In the thread about Radio Jay Allen’s excellent tuner & receiver reviews I mentioned he revealed a problem I had with a Grundig SATELLIT 750 radio, and there are other problems Radio Jay hasn’t addressed.
Problem # 1 had the AM band sounding like stations weren’t tuned in even when the LCD indicated the exact frequency, such as 550 kHz. Indeed it wasn’t tuned properly as Radio Jay explained there was an error that put the frequency center 3 kHz high, which means I need to tune 553 kHz to properly hear 550 kHz. That’s easy to do, but the next problem isn’t.
Problem # 2 is that the strongest AM signals sound distorted as if something inside the radio is clipping the audio circuit on strong stations. Weaker AM stations don’t sound distorted.
Problem # 3 is a noisy jumpy volume control that scratches and leaps in volume when it’s turned, perhaps a bad solder.
Problem # 4 is that all put 2 screws allow removal, the last 2 being so tight that applying force will probably strip their Philips heads, preventing from getting inside.
Now the technical members have something to weigh-in on.
- November 22, 2018 at 1:44 pm #107458
Problem 1 you found away to improvise but is caused by a misalignment. Sometimes digital tuning is not true digital tuning(PLL) but digital readout with analog tuning. This is most likely why you are finding what you said. If you have a tuning cap or varactor diodes you don’t have true digital tuning.
Number 2 is an AGC malfunction and
3 is a pot that needs some electronic contact cleaner to work like new again. Not a solder thing. The static is because of bad electrical contact when moving and it jumps in volume because it is not a smooth resistance change.
You can try to turn the screws to get inside but make sure the philips fits snugly in the slots and doesn’t have play. Then you won’t strip the screw slots.
The distorting on strong stations would need a schematic to see what does what….if it was an amplifier thing it would distort on weak stations too if you turn the volume to the same level.
- November 22, 2018 at 3:13 pm #107461
Good Engineering Advice
Mark said: “The distorting on strong stations would need a schematic to see what does what.”
I once asked Universal Radio, the place where I buy most of my radios, if I could order a schematic for my Grundig U1, which also has some issues, and they said they cannot get schematics on any of their radios.
Back in the past it was possible to order “Sam’s Photofax Schematic Packs” or service manuals, but the consumer now is being left out.
- November 22, 2018 at 4:15 pm #107465
Some Radioshack radios came with the schematic right in the back of the owners manual.
- November 23, 2018 at 2:37 am #107467
- November 28, 2018 at 7:32 am #107522
Stereo Mono Options and Choices
The audio chain is as much a technical matter as the RF chain.
Thinking and planning the stereo-mono handling of audio can get complicated.
Let’s say that we start with a stereo audio signal and watch what happens to it as it passes down the chain to a monitor speaker system, transmitter, or stream server.
Of course an audio signal can exist in hardware form: inputs and outputs to amplifiers, processors and transmitters, or it can exist in digital form passing between apps in a computer.
For purposes of this discussion let’s use Zara as the starting point. The Zara playlist can contain various kinds of audio files including both stereo and mono, but it definitely has 2 channels output and cannot be configured to output mono.
So, when a mono audiofile is played in Zara we believe it gets output on both the left and right channels. So Good so far.
Next stop is the StereoTool Audio Processor Stand-Alone Version, which also is inherently set for stereo and cannot be configured to mono.
But looking ahead we realize that the web server will be sending in mono, so we want an L+R mix, a mono signal that contains both the left and right channel information blended together. Toward this end we set the B.U.T.T. Encoder to mono. But what does that do?
Does it give us an L+R mix? Or, does it send only the left channel and call it mono?
This example of stereo mono uncertainty is fairly simple and we can find the answer through analysis, but other apps and situations also have confusions and it does not seem possible to fully know what to expect in every situation.
- November 28, 2018 at 1:52 pm #107529
Recently, I had an issue with Mono vs Stereo that caused me great grief until I solved it.
My FM transmitter will transmit in either mono or stereo. I had it set to mono. I assumed that it would mix the Right and Left Channels of a stereo input, just as a Decade MS-100 and other Decade transmitters would.
Sometimes assumptions are incorrect.
Most of Artisan Radio’s programming is mono. Some, however, is stereo, when no mono version exists.
I ensure that streaming, when present, is mono, by using a Mono VST plug-in.
I was noticing, however, that occasionally songs broadcast over-the-air sounded ‘funny’, as if some of the track was missing.
It turned out that although the input jack to the transmitter accepted a stereo plug, the transmitter itself only took one channel (not sure which one) when transmitting in mono. So the few stereo tracks that I had were missing one side.
I resolved the issue by mixing down the two audio channels to mono (in hardware) before the input to the transmitter.
But the moral of the story is … never assume.
- November 28, 2018 at 7:45 pm #107535
“I resolved the issue by mixing down the two audio channels to mono (in hardware) before the input to the transmitter”
Hopefully with more than just a plain wire Y-connector type combiner?
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