I can use some advice on a problem I am experiencing with some projects which use the BH 1415 Chip.
I can use some advice on a problem I am experiencing with some projects which use the BH 1415 Chip.
I have purchased a few different types of transmitters over a period of time. You know how it is, you buy stuff then hope some day you will have the time to work on the projects. Ok well, I now have the time, and after testing this and that product, I was really disappointed in some of the transmitters I have purchased. The reason is in just about all cases there is considerable noise and distortion in the audio, see next paragraph.
At the gentle fade in of music, where the volume level is naturally low, and also at the fade out of music, where the volume level fades out. The music will get “grumbly” sounding. If I put in a very low level audio and hold it at that level, the distortion can be plainly heard. As the volume is boosted, then the sound will become a lot more clear. This is not just something you have to lay your ear into to hear. You can hear it with out going to any effort, this is not some whisper little noise or distortion. Any body off the street would identify the distortion, you don’t have to be an audiophile to note it.
I also have transmitters which use the BH 1417F and BA1404 and the distortion noise does not exist. I checked several times over and over again and they are clean to the ear. I have the basic schematics on the BH 1415 chips, but for the most part I don’t have any schematics for the transmitters with the problems.
These are Chinese transmitters, ok I have heard the bad mouth about spurs on these and on the harmonics, but that is not the question I am asking here, the question is why does this distortion exist and how can I get rid of it?
I am not sure if this is a MPX filter issue, or a modulation problem. I really haven’t looked into it technically because most of these boards are SMD and I don’t have schematics on them anyway. To me from my experience it appears this is a problem with affiliated components which the chip relies on for proper operation, but I could be wrong, I cant possibly believe that this is the way the BH1415 would operate and its hard for me to understand why anyone would or could tolerate the distortion.
I have three transmitters all the same make and model, and they all have the same problem. I tested two other BH1415 chip transmitters that were both different designs and same distortion.
I have some transmitters that use the BH 1417F and these all work very good , good clean audio.
I haven’t checked any thing on the transmitters yet, just pulled them off my dream transmitter shelf and put them in a box under the work bench, maybe you can relate. Maybe it’s simple, like too low VCC. I know the power in is fine, and output RF power is great, tested with a watt meter and 50 ohm dummy load.
Need some help on this topic by anyone who has built and designed using the BH chips.
Thought I knew it all but I know nothing it looks like.
Thank you,
Radio Joe
I also have transmitters which use the BH 1417F and BA1404 and the distortion noise does not exist.
I have some transmitters that use the BH 1417F and these all work very good , good clean audio.
Might just be a bad batch.
Not sure what the purpose is, but these things are relatively cheap. Why not pitch the BH1415 in favor of one of the others? I.e., if it's just the stereo, you can get a multiplexer NJM2035 for the BH1417 for the same price and have everything you want.
I have an old FM tx. based on the 1404 chip which is frequency controlled with an L/C oscillator. It sounds as you describe when the carrier drifts off frequency. Though your units are most likely crystal or resonator controlled the mfg. could have used a bad batch. How do they sound on an analog tuned receiver?
Neil
Analog tune digital tune all is the same, and I have checked the frequency of the tranmitters wiht a counter... this seems to be a problem more wiht the 1415 chip than anything else. The 1417 transmitters are clear as a bell.
Most transmitters with the 1415 chip will be ones with full 88-108 coverage, or more. The 1417 chip has frequencys selected by DIP switch. Some frequencies in the low end of the band some frequencies at the high end.
No mater which transmitter I tested, and I have a "few" any of the BH1415 transmitters, will show this distortion except one paticular model and make that I have.
Some one recomended changing the chip but most of these are under another circuit board and up on risers with the boards soderded together, just a lot of hassle for what its worth to take apart.
From what I understand, the 1415 and 1417 are similar chips but the 1415 you need a special controller to change frequencys, its a more advanced chip, but the basics are the same as far as the RF part, so I have heard, but thats part of what Im trying to find out also, because the problem seems to ge with the 1415 chip not the 1417.
The distortion is easy to hear, just turn the input volume down low into the 1415 and listen for it on your FM receiver. the lower the volume is adjusted, the more distortion you will here in the program signal. The same distortion is there if you hit the mono button on the receiver too, and I have listened to the distortion on a few receivers and all have the same distortion so its not the receivers.