Greetings my friends of electromagnatic and electrostatic radiation!
I purchase a lot of BH 1417 and 1415 chip based transmitters for personal learning experiences in hopes that I may someday, through my carefully documented experiments provide enrichment to the science of radio technology.
Over the years I have had many of these transmitters that worked perfectly, however three of them would not transmit stereo.
These transmitters would light the stereo indicator light on a receiver but the left and right channels were combined so there was no separation. (Yes, the audio source was two separate channels)
Two of the transmitters were “factory built”. On those transmitters I traced back from the audio input jack all the way to the chip (with audio source) to make sure there was no connection between the channels before the audio got to the chip. That all checked out so then I replaced the chip, that didn’t change anything the audio was still mono on the receiver. (Analog tuned) Then I replaced some parts leading from pin 8 (BH 1417f I think its pin 8, if not it’s the pin on the IC which sends the composite signal to the oscillator.Doing that didn’t change anything either, the output was still mono. I never changed the varactor diode but that is about the only thing I didn’t change. I did change the crystal and that didn’t make any difference either. I checked the frequency to make sure the transmitter was right on and it was.
Ok so I gave up on those two transmitters, I sent them back to China and never heard back from anyone so the transmitters are gone forever.
Then recently I bought a kit transmitter that I had to assemble. This transmitter works great but to my HORROR, it has just about the same issue as those transmitters above. The only exception is that there is a bit of stereo separation but a far cry from what it should be.
For trouble shooting, I did all of the above to this transmitter, including tracing the audio from the input jack. I also ended up replacing the BH 1417F chip and some related parts but still no separation. Just to note, when I put an audio signal into lets say the right channel the same audio is transmitted from both channels. This is the same as from the left channel.
For now I gave up on this one also, too bad because I had spent the evening making a nice case for it. I decided to order a second kit and will try that one to see if it works properly or not.
I understand that a person can tap off of pin 8 (I think its pin 8 on the 1417F) the composite signal and run it through a different oscillator to see if I get a good stereo signal that way, but for now I have better things to do.
Does anyone have any idea what is causing this problem of no stereo seperation? Like there are only a few external parts to this circuit, and I did replace the chip so that doesn’t leave much to go wrong. Once again I tested to make sure the audio channels were not being combined prior to getting to the input on the chip.
I hate to admit RADIO JOE is stumped. It is very hard for me to accept that I dont know the answer to this problem!
BH 1417F? I knew abut the BH 1415 and BH 1415F chip set from Rohm, but never heard of BH 1417F. Is that what these Belkin's use now? I had a Belkin Transmitter a few years ago that did the same thing. The Stereo light would come on, but little or no separation. One of my Radio's would separate, but the transmitter almost had to be touching the antenna (Really). I understand that there is two stereo signals that do make up the FM Stereo signal and if one or the other is out of phase the receiver will have issues with the separation. The pilot is 19KHz and the other is 38KHz. Often the 19 Khz signal is either under driven which would cause the stereo light not to come on. The other case is Over driving the 19 KHZ signal to where it is way above the signal of the 38 Khz signal which is the actual separation. If the 38 Khz signal is higher than the 19 Khz signal often you'd hear a lot of noise on the left and right sides and becomes hissey even at close range. Often the pre emphasis on the Chinese transmitters is set to 50 uS eq and not 75 uS eq. This causes the highs to roll off and becomes muddy. Often there has been reports of a blinking stereo light wen modulated. Depending on the receiver it could cause issues just based on that alone. The other is I'm wondering if there is issues with the BH 1417F chip set to where these are cheaply made and worse than the BH 1415 series chips. I'd like to know which Chinese transmitters have these. The SainSonic and CZH units uses the BH 1415 series, but when the new TNC connector series came out it seems as though they have cheapened these units even more. There is a portable CZH-T200 unit but I still think it uses the BH 1415 series chip. I know that this chip supposedly has a limiting circuit in it that is suppose to keep from over deviating due to over modulation. Yet some of the transmitters I've seen don't really have any sort of limiter that I can tell and are easily over modulated if you don't already have a compressor nd limiter either virtual via software or hardware based. What is the brand of transmitter your talking about? This may help as well. Thanks.
Hi Radio Joe: Things to Do.
1) Never Buy the chineese Junk in my research i been seeing allot of people been having issue even with no response back or stupid response back from company(s) i have gone through this personally myself as well !!!!!
NOTE: Pilot Generator is a 19 Khz signal !
NOTE: Stereo Seperation Is a 38 khz Generator !
2) First off download the PDF of the chip your working on !
3) Download a schematic of the transmitter your working on !
4) Check all your solder joints and part to make sure there not bad !
5) Check your crystal out and if they didn't use a crystal did they use a lc tank circuit and did the parts go bad.
6) Make sure you don't have any solder joints where it doesn't belong ! Note: Use a maginifer to make sure.
7) Depends on the circuit you have to make sure your balance control / setting needs to be set right or you could have issues.
8) Keep in mind depends on the stereo seperation circuit you will either get from a very small seperation to a large seperation on how circuit was constructed.
9) You need to send a tone through your L & R channel seperate for a check.
When i bought a vectronic kit it wasn't very old and i lost the 38 khz stereo seperation and found out my crystal went bad i replaced it and it worked just fine now!
I have gone through some of the same issues and mine cleared up quick i hope some of these idea's helps out.
Station 8