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I’m wondering if you folks can help me with a problem I’m having:
I’m wondering if you folks can help me with a problem I’m having:
I have a 500mW FM stereo transmitter that I acquired to transmit streaming audio (pandora.com, last.fm, etc.) and MP3 files from my laptop computer to the various FM radio receivers in my home, and possibly to the FM receivers of interested residents in my condo complex who seem to dig my musical taste! (Unit is: mobileblackbox.com, Eclipse-4000).
The transmitter has a BNC-connected 6.5″ rubber antenna, and I output the sound from my computer’s headphone jack with a 5′ cable with 3.5mm stereo plugs into the transmitter’s line-in jack.
The problem is that the sound coming from my FM radios is scratchy (mostly on the higher, treble sounds). It’s not an overload or distortion sound (I have all of my volume settings carefully adjusted). It sounds like an FM radio does when it’s slightly off frequency. This happens both when I’m streaming audio from the Internet or playing MP3 files with Windows Media Player.
I’ve tried:
-moving the computer and transmitter to a different room
-plugging the transmitter into a different electrical circuit
-turning off the laptop’s wireless capability and using an ethernet cable
-moving the transmitter away from the computer (5′)
-completely unplugging my nearby DECT 6.0 cordless phone
-I’ve tried every FM frequency available: 87.9, 88.1, 88.3……107.9. (The lower end of the spectrum sounds somewhat better, AND, I realize that I’ve got to settle on an unused frequency once I get this situation sorted out)I know that the transmitter is OK because when I plug my portable MP3 player into it, the transmitted sound is excellent.
And I know that the headphone jack on my computer is OK because it works fine with my Altec Lansing powered computer speaker system.
Finally, range isn’t a problem: When I drive away from my home, I can hear my “station” until I reach 6/10-mile away. When I set my transmitter to transmit in mono, the sound on my FM radios is “almost acceptable.”
I made a tech support inquiry with the manufacturer of my transmitter (as above), and they replied:
……………………………………..
“The problem may be that the antenna is too close to your laptop and/or your laptop is still producing some kind of interference into the FM frequency.If you have access to another laptop to test the transmitter you will probably not have the same interference.
I’m not sure if this will work, but what I would try is the 33″ telescoping we have in stock which also includes a 10 ft. cable and magnetic base.”
……………………………………..I’ve tried the manufacturer’s suggestions, to no avail. Any ideas on what’s happening, and how I might remedy the problem?
Many Thanks,
Carl
Total posts : 45366The input for your transmitter can be A-OK and your PC Sound card output can be working great, but there might be an impedance mis-match between the output and input that distorts the audio without overloading the input level.
One of the Talking House transmitters I use has a somewhat peculiar input impedance and I had to use a matching transformer (8-1000 Ohm, CT) to get clear audio. You could also try running it through a mixer for a better impedance match and some pre-amplification.
There also might be some PC crud (a PC is a nightmare of RFI) sneaking up the audio cable. Perhaps try an isolation transformer in the audio chain.
The telescoping antenna should be fine, can’t imagine how that would gaak the audio.
Total posts : 45366I’m going to try your potential solutions:
– “isolation transformer in the audio chain”
– “a matching transformer” (Does this refer to the power brick on my power transmitter’s power supply cord?)
– running my computer output through an (indexpensive?!) mixerCan you direct me to sources for these, and clarify exactly what I should be asking/looking for? The isolation transformer sounds like the simplest fix (just guessing). I vaguely remember a situation long ago when I had a microphone with an 1/8″ plug that would give me the same kind of bad audio output from a cassette tape recorder. The simple solution was an adapter from Radio Shack: it was an 1/8″ plug with an 1/8″ jack on its other end. I’d plug this adapter into the tape recorder, then plug my microphone’s cord into the amp, and the recorded sound was then perfectly clear. I think this had something to do with impedance, but I don’t even remember what the gadget was called. It’ll be great if my current problem could be fixed so easily and inexpensively.
Thanks again…
Total posts : 45366Your problem may be much simpler that what follows but I offer this as a possibility. This has happened to me and the cause was due to the high frequency components in the audio mixing with the 19 kHz pilot in the transmitter and disrupting the stereo signal. This is common in low cost transmitter which do not low pass filter the audio input so the frequencies above 15 kHz are not attenuated.
Some of your audio sources may contain high frequency inaudible material such as digitizing artifacts while others don’t. This would explain why you have the problem with some sources and not others. It also varies with program material. The solution is to place a low pass filter (15 kHz) in line with the audio inputs. I believe Ramsey Electronics offers such a device as an “audio processor” or if you are inclined you can build your own.
I did a quick read through about your transmitter on the mfg. site and saw no mention of an audio filter being included in the transmitter. You might ask them about this before spending a lot of time pursuing this idea.
The suggestions in the previous postings are worth a try, but if they do not work an audio filter may be needed.
Here’s a link to another board where this type of problem was discussed and the poster was able to solve the problem with a home brew filter:
http://www.ramseyelectronics.com/forum/showthread.php?t=3357
Neil
Total posts : 45366>>”isolation transformer in the audio chain”
Here’s one made expressly for your purpose
Pureformer Isolation Transformer
“The Pureformer isolates the electrical grounds of two pieces of audio equipment. This is especially important in the case of computer audio cards connected to high quality/low noise audio equipment. The computer electrical ground is often filled with noise from disk drive activity and data transmission. Many audio cards use the same electrical ground for the computer and the audio signal. When the computer audio card is connected to your studio equipment, the electrical noise from the computer can leak into the rest of your audio system.”
>> – “a matching transformer” (Does this refer to the power brick on my power transmitter’s power supply cord?)
No, it’s a passive device that can help bridge an impedance mis-match in the audio connection, example:
VALCOM VMT-1 INPUT MATCHING TRANSFORMER
>>”(indexpensive?!) mixer”
You could try a Behringer XENYX 502 Stereo Mixer or check ebay.
>> “I vaguely remember a situation long ago”
Possibly an attenuating dubbing cord
Total posts : 45366I have had a problem here with my ramsey fm25b that tends to be over the top when it comes to treble, ive heard distortion on a cheap Durabrand boombox that made the sound almost the way you described yours. I moved the radio farther away from the transmitter and some of it cleared up, the rest of the noise was artifacts from the fm25b.
As i said the 25b has in my opinion too much treble and not enough bass or almost no bass. I think i found the solution or fix for the 25b’s lack of bass response. But anyways, i went out to my pontiac transport wich has a factory am/fm cassette radio, the noise was non-existant out there wich led me to believe the receivers in the house are just getting slammed with rf.
Did you hear the noise you mentioned on a radio that may be further away?
Im just guessing here, the above solutions maybe a better fix than mine. Good Luck
Total posts : 45366rock95seven: I’ve tried radios at many distances from the transmitter; from a radio placed a couple feet away on my desk, all the way to 1/4-mile away in my car. The sound is ALWAYS identically the same. And I’ve carefully adjusted my volumes (system, media player, etc).
Thanks for everybody’s help and suggestions thus far!
Total posts : 45366As far as identifying my “problem sound” with a technical term, I’m now quite certain that it would be called “clipping.” I verified this by watching a YouTube video in which a guy discusses and demonstrates audio clipping (as it relates to a high-end video camera microphone). The samples of clipping that he uses (with voice, solo instruments, music) leave no doubt to me that that’s what I’m hearing.
Maybe this will help you experienced guys in steering me towards the most viable of the several fixes mentioned above. (It could get pretty expensive for me to work my way through the fixes!: buying a low-pass filter, buying that transformer gadget…)
Total posts : 45366I don’t know if this is pertinent to the discussion that I’ve started here, but my transmitter has Auto Gain Control – “Automatically adjusts input volume level to prevent distortion in FM
receiver.”From the manual:
“When powering the transmitter unit OFF; allow transmitter unit to reset (discharge) the
AGC circuit controller (about 10 minutes) before powering ON again.”Here’s a PDF of the user’s manual:
http://tinyurl.com/eclipse-4000(Pardon my barrage of postings on this; but I’m really scrambling to get this transmitter working properly for an upcoming project.)
Total posts : 45366vermonter,
Don’t apologize for your “barrage” of posts. That’s how you will learn and that is why this board and we posters are here, and here is a learning opportunity for you:
If you think your transmitter is clipping a simple way to verify this is to reduce the audio amplitude into the transmitter. At very low input volume do you still hear the distortion? Things are complicated apparently since the transmitter has some AVC built in which may function to keep the audio at an unacceptably high level regardless of the feed volume.
Now for some unpleasant information which many don’t like to hear yet it is what it is and it can keep you out of trouble. According to the specifications from the manufacturer and your reported range test results your transmitter is illegal with respect to part 15 rules. Since you are new to this I am offering the following information, but keep in mind that FM hobby transmitter operation can be legal and if you read on, you will gain information about this.
First, it is not legal to sell in the US an assembled transmitter which is not FCC certified and your unit is apparently not. This is between the seller and the FCC and shouldn’t be a problem for you except when you are caught operating it outside the limits of the rules.
Kit transmitters such as the Ramsey line are legal to sell without this certification yet keep clearly in mind that the use of such devices outside the FCC rules places the burden on the user and not the kit provider. There are others such as the Belkin and CCrane lines which are assembled and certified and should be no problem to put on the air.
The FCC rules do not specify the power output of an FM transmitter; they specify the field strength at a distance and this has nothing legally to do with power. A transmitter which provides 500 mW of power will certainly produce a field strength which exceeds the limits and will be illegal to use with almost any antenna. In fact, it is commonly known that a power of around 11 nanowatts (500 mW is about 45 million times this power) using a 30 inch antenna will produce the maximum legal field strength. A legal field strength with a typical receiver will produce a range of just a few hundred feet as opposed to what you have reported with your transmitter.
You may choose to continue but you should know what consequences you may have if you are caught and cited by the FCC.
Now for some encouraging information. Many of us use and enjoy our part 15 FM transmitters and stay out of trouble. There are two ways to do this. Purchase a FCC part 15 certified transmitter and use it as instructed or build one from a kit and set the range to about 200 feet or so and enjoy your on the air time. Using a “500 mW” transmitter is just inviting trouble, especially since your signal is apparently not clean. I advise returning this to the manufacturer and getting a refund and then doing some research, such as asking questions here, about how to do this legally.
Any questions from you or others regarding this are welcomed and I will do my best to help.
Neil
Total posts : 45366The Eclipse 4000, was made by HLLY a Chinese company famous for poor audio quality, high spurious emissions, poor harmonic filtering and being off frequency. We have a warning about these transmitters on our website; MobileBlackBox simply changed the color of the case and stuck their name on the HLLY transmitter.
http://www.hllyelectronics.com/html/fm_transmitter_1_59.html
Being off frequency could be a problem, check to see if the effect is as audible on analog dials.Even with a high quality transmitter like an EDM LCD transmitter, improperly equalized audio can wreck havoc on the transmitted audio; with the type of distortion you describe. With a mixer and a equalizer, making the audio acceptable for broadcast can be a challenge and still have it sound right. I would put an audio processor like the Behringer DSP 1425P between your audio source and the transmitter, starting with an audio level of -10db. Short of that, see if your audio card has an EQ on it; if so, pull anything above 15k to the minimum setting. We have to do that with some of our feeds to make it acceptable for broadcast. You should also check the audio level to the transmitter, it may still be overdriving it.
I just had to deal with this problem with one of our FM stations, all the meter levels were correct, the EQ was set right; yet we were still getting that high end clipping. Turns out the Audio Master processor’s meter feeding the compressor was set to +8db scale, so when the meter was reading 0db it was really +8db and slamming the processors front end; causing the clipping. Because of that switch, all the levels looked normal yet were killing our audio with high end distortion.
All transmitters I have used over the decades except the EDM’s have needed an equalizer to clean up the audio. The EDM LCD is the only transmitter you can run bare bones and still have it sound outstanding on the air.
Since you really have an HLLY under the hood; one of the many names the Chinese company uses, and live in a condo, you might want to make sure it’s not trashing nearby radios & televisions with its poor harmonics and spurs.
I noticed HLLY is gone from E-bay, could be to many make goods for Paypal, here is a link to the company that made your transmitter, it now has a new name: http://www.vhf-fm-transmitter.com
While the EDM LED may not look as cool as the HLLY; it walks circles around it in terms of audio & RF performance and the price is about the same.
Total posts : 45366(Again, I greatly appreciate the effort you folks have put into your replies. And, I’ll be giving those “legal implications” issues some serious consideration.)
Here’s a summary of where I stand in working on my problem:
The clipping problem is only heard on FM receivers when I use my laptop as my audio source (through the computer’s headphone jack). The clipping is heard whether I’m playing MP3s with Windows Media Player or streaming audio like pandora.com.
I get loud and clean FM output (CD quality) when I use any other available audio input source that’s been available for testing: my own portable MP3 player, friends’ two different iPods, the stereo RCA audio outs on my 32″ TV — and I even plugged a portable FM radio into the transmitter.
Shortly, I’ll be able to try another input computer (or two, or three).
As one of you suggested, I contacted mobileblackbox.com’s tech support and asked if my transmitter’s circuitry contains any filtering; it doesn’t.
I can place the transmitter a few inches away from my laptop and plug an iPod into the transmitter’s input and the sound from FM receivers is excellent. So interference from the transmitter’s proximity to the computer probably isn’t an issue; the physical connection from the computer to the transmitter via the 1/8″ stereo cord seems to be where I’m getting in trouble. Could something as simple as an “attenuating dubbing cord” (mentioned in a post above), or some simple means of matching impedance be a possible fix?
I plod onward…
Total posts : 45366For some reason, some computer outputs have an impedance that is incompatible with transmitters. This problem has also affected users of EDM LCD transmitters; some have reported success with the attenuating dubbing cord. Since the cord would cost the least to try that should be the one you try first.
For all micro-power broadcasters:
Regarding interference: One simple test for spurious emissions is to tune across the FM dial and see if your signal pops up else ware. For harmonics tune your transmitter to 98.3 then turn a nearby TV to channel 10 (your channel 10 needs to be active), some minor hare boning may appear in the picture (wiggly lines). That would indicate your transmitter has pretty good harmonic suppression, if the picture is the wiped out; you will have a problem with your neighbors and the transmitter should not be used.Regarding your power levels; if you are in a condo community (private property) and using the supplied antenna, you should not worry about the Feds knocking your door down. Ramsey and others sells micro power transmitters like yours by the thousands, those transmitters are not going to cause harmful interference anywhere near the level IBOC broadcasting causes. The FCC seems to turn a blind eye towards IBOC & CFL interference that wreck havoc on radios across America, they also seem to give a pass to the countless pirates running 100’s of watts and using every four letter in the book in New York & Florida.
If the FCC started targeting micro-powered broadcasters, while ignoring the others; there would be a public outcry you could hear from coast to coast, and it would be a public relations nightmare the FCC and NAB may not be willing to deal with. The NAB, the driving force behind the FCC has concerns about its members being forced to back their local communities (very costly). Micro-broadcasters fill a void left in communities where the mega corporate broadcasters have left, having thousands of micro powered transmitters in the field has proven that they can coexist with full power broadcasters; causing less harmful interference than a CFL (compact florescent light) generates. Once the NAB understands it’s to their advantage to have micro-broadcasters come in and fill a void in communities vacated by full power broadcasters, they will relax their concerns and so will the FCC.
The last thing NAB member’s want is to be forced back to their local communities, besides right now Wi-Fi broadcasting is a far greater threat to them than a 250 milliwatt neighborhood broadcaster will ever be.With proof in hand that micro broadcasters will not cause the harmful interference anticipated, we might be able to justify higher powers legally like the 300 milliwatts allowed in New Zealand and 10 watts in Norway.
Be responsible with your transmitters and programming, and we might be able to get the rules changed sooner than later.
Total posts : 45366Vermonter,
Carl,
You have received much advice from us including the legal stuff. Back to the original post problem you mentioned and considering the subsequent posts it seems that there is something going on with the audio output from your lap top. Have you tried listening to the audio from your lap top on headphones? Perhaps there is something wrong with this. Do not hesitate to keep us advised of your experiences and ask more questions if you think we can help.
Now, let me respond to Steve’s reply in the previous post which may be a bit off topic but bear with me.
Steve wrote:
…If the FCC started targeting micro-powered broadcasters, while ignoring the others; there would be a public outcry you could hear from coast to coast, and it would be a public relations nightmare the FCC and NAB may not be willing to deal with….
By micro-powered broadcasters I have to assume that this refers to part 15 AM and FM operators and if not then my remarks should be disregarded and with a reasoned reply I will stand corrected. Steve, I know from your many previous posts and by visiting your web site that you have accomplished remarkable things but I have to question why you state there will be a public outcry if microbroadcasting (assuming you mean part 15 stuff) is targeted by the FCC. I would like to believe this but experience has taught me otherwise. I have been a broadcast radio DXer and part 15 operator for over 50 years and I have never heard another micro station on the air except for a Talking House which went away within a week. I know of only one other part 15 station near me in Marysville, Ohio which is about 15 miles distant and I cannot hear his signal. Given your experience what makes you think there will be a “public outcry” if the FCC clamps down on part 15? Pardon me if I take this out of context or make statements from ignorance but could you please elaborate. I don’t believe the public knows about nor cares about microbroadcasting. unless your definition differs from mine.
I also do not see any chance that the rules will be changed in the foreseeable future pertaining to part 15 operation. As I recall you recently obtained a license for a low power operation and, if so, congratulations, and if licensed low power operation such as this is what you mean by microbroadcasting where the effective range is more than a few houses down the street then I am all for it, but please clarify if this is what you were referencing.
Neil
Total posts : 45366“For some reason, some computer outputs have an impedance that is incompatible with transmitters. “
I agree, especially the mobo-native sound chips. I’m guessing low, because of other mis-match issues I’ve experienced, but I don’t know for sure. If the sound card is in the 300 Ohm area and the XMTR in looking for 600 there could be some clipping-like sounds, especially with the probably-lacking audio input buffer amplifiers on the audio input side of the XMTR. My Gizmo AM unit sounded *much* better with an LM 386 in front of it.
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