radio8z:
I usually have a powered Altec Lansing computer speaker system plugged into my laptop's headphone jack; it sounds great. So do headphones. So apparently the sound card and headphone jack are good.
I'm going to try an attenuating cord from Radio Shack today, and see what happens. That'll be inexpensive, and it won't hurt to have an extra cord lying around if it doesn't solve my problem.
Plus, later today one of my condo neighbors is going to let me plug my transmitter into his desktop computer so we can see how pandora.com sounds coming from his machine.
Sounds like you are on the right track with troubleshooting this. It is very possible that if you are using the speaker or phone output from the laptop that you are over driving the transmitter. If it works, the attenuation cord would be a nice and simple fix.
I recall mistakenly plugging into my portable CD player's headphone jack instead of the line jack when I was trying to dub some audio and the result was pretty miserable.
Let us know how this turns out.
Neil
Ahhhhh... What is sounds like based on what you're describing as a problem with high frequency sounds from your program material competing with the 19 KHZ pilot. An easy work-around is installing an equalizer between the source and the transmitter. Then you "hard limit" anything above 15 KHZ. Carefully adjust your audio so you don't over-deviate (75 KHZ) and you're good to go.
I know that 500 mW EIRP is allowed for unlicensed FM broadcastin in New Zealand, but I was surprised to learn from RADIOBRANDY that 10 W is allowed in Norway. I was not able to find out anyting about the LPFM rules in Norway on the Internet. I would really like to know more about this. I wonder if RADIOBRANDY can cite some reference.
So, vermonter wrote with a great question about cleaning up audio issues and some great responses were posted for that need.
Now the conversation is shifting to policy issues.
From a visitor's perspective it's a much nice user experience if threads are topic driven.
The policy issues here are interesting and valuable, just not congruent with solving audio issues in low power transmitters.
A new thread for policy discussion has been started here:
http://part15.us/node/1908
How about policy there, audio clean up here.
Policy came into play here, when someone beat the tired old drum again that operating a transmitter with 500 milliwatts is illegal and the FCC is going to knock the door down and hit somebody with a big fine.
I feel it's important to keep people in the real world and a little perspective was is in order. Vermonter should not live in fear turning his transmitter on with 6" indoor antenna in a condo complex on private property is going to cause the feds to come in and knock his door down and hit him with a big fine. Anymore than a cop is going to pull him over for doing 56 mph in a 55 mph zone, when the other 1000 drivers are doing 75 mph, talking on the phone, drinking a beer while weaving all over the road.
The other part had to do with being responsible with his transmitter, checking for harmful spurs and harmonics and being careful what is broadcast on the transmitter; keeping in mind that programming is more likely to lead to a visit and a fine regardless of the power and antenna.
It was Howard Stern's foul mouth show that lead to complaints and the FCC to go after Sirius & XM radios for excessive power, not just the fact they were interfering with other radio stations.
Vermonter being new here, may not have a understanding of the complexities of the issue or where to look here for perspective on the issue.
For the record: The output power of the HLLY/MobileBlackBox transmitter is closer to 100 milliwatts, based on the 15 samples we tested. Only after internal tweaking were we able to pull up the power which never made the claimed 500 milliwatts. Having tested 15 samples, some were within reason when it came to harmonics and spurs, while others were way out of spec and dangerous to use. I think it is important for Vermonter make sure he got one of the better ones. With a little internal tweaking and quality control, they can be good transmitters; not as good as EDM, but far better than Ramsey for the price. MobileBlackBox should double check their transmitters before they ship them out, I know from our samples; HLLY does not do any QC.
Steve
Realistic Broadcaster
(Steve: Thanks for that eye-opening insight into the manufacturer and the specs on my transmitter. I do hope I got one of the "good ones.")
Well, today I had the opportunity to further test my transmitter by plugging it into the headphone jacks on three other computers residing within my condo complex: two different Dell laptops running Vista and XP, and a brand new 3.2 GHz Mac Pro running OSX Leopard. On 88.1 FM stereo, we broadcast pandora.com, and MP3s via Windows Media Player and iTunes. The output from all of the FM receivers that we tried was beautiful. I was glad to get these results as I now know that the clipping problem originates with my Toshiba Windows XP laptop. It's just too bad that every other audio input source works flawlessly, and the most important input source for me -- my laptop -- is problematic!
I checked at our local Radio Shack for that "attenuating dubbing cord" as a first inexpensive try at a fix, but their cord is mono. Is a stereo version available elsewhere? If not, I'm thinking that maybe the idea of a simple mixer may be next. scwis suggested a Behringer XENYX 502 Stereo Mixer. wdcx suggested "an equalizer between the source and the transmitter." Is that the same as a mixer? Any specific make/model/where-to-buy recommendations?
Continued thanks, brothers...
Vermonter,
I am beginning to wonder if the "attenuator" cable will help since your xmtr. worked with the other computers. It seems unlikely that their outputs would differ from yours in terms of level and impedance. I still suspect that there is some artifact coming out of your laptop which is interfering with the stereo pilot, but that is only conjecture.
A mixer allows one to combine audio signals from multiple sources and you can control the amplitude of each signal. An equalizer allows one to set the frequency response of the audio system by providing several filters whereby the user can enhance or attenuate various frequency bands in the audio signal (think "tone controls"). John's suggestion of using an equalizer has to do with cutting all frequencies above 15 kHz out of the audio to prevent interference with the stereo pilot signal. Hope that helps somewhat.
Steve is correct about the "old drum" being beaten regarding legal operation. He is also right that you are new to this and that is a good reason for you to hear the drum, at least once.
Neil
Now I think I'm getting somewhere, Neil. After a Wikipedia search on "pilot signal," I now have a good basic understanding of what that term means ("In telecommunications, a pilot is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes...").
One thing that leads me to think we may be on the right track here is the fact that my transmitter provides a fairly decent FM broadcast when set to its mono mode. Just amateur speculation; I hope that logic makes sense.
There's nothing unusual about my computer setup, so there's probably not much hope of eliminating this problem from the laptop side of the equation.
My next step will be to try the mixer/equalizer route. From what I've read above, it sounds to me like the equalizer is probably the most sensible first step. Any make/model/where-to-buy suggestions on mixers and equalizers would be greatly appreciated.
I'll keep the forum updated.
Does anybody think I could accomplish the necessary audio cleanup with this inexpensive Radio Shack "4-Channel Stereo Microphone Mixer"?
Description on Radio Shack site:
http://tinyurl.com/4ChMicMixer
PDF of the mixer's user manual"
http://tinyurl.com/MixerManual
Better pics in an eBay listing:
http://tinyurl.com/eBayMixer
It looks like I'd need two identical cords: 1/8" stereo on one end, and RCA red & whites on the other end. I'd stick an 1/8" plug into the computer's headphone OUT, and connect the RCAs to the mixer's AUX 1. Then RCAs into the mixer's OUTPUT, and 1/8" plug into my transmitter's LINE IN. Looks simple enough. But, will I be able to manipulate the sliders to eliminate my clipping problem? Or will this just add another volume adjustment to my rig?
If the problem is from interference to the pilot signal then you need a graphic equalizer rather than a mixer.
You should already have a software mixer on your system whereby you can adjust volumes of various channels and the output volume and balance. (Windows Volume Control does this).
Neil
Ramsey makes this processor for FM transmitters:
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=STC1C
It is a kit so you would have to build it.
In the description they say:
Low cost CD players that have poor filtering on the output are really cleaned up by the switched-capacitor low pass filtering in the STC1. Higher order harmonics and clock feed-through that causes annoying heterodynes and whooshing noises disappear.
I don't know if this is what will work for you or if you want to go to the trouble and expense to find out. You might do better on ebay if you can find a graphic equalizer.
Neil
I'm going to try a new "Behringer FBQ800 MiniIFBQ 9-Band Graphic Equalizer."
.................
"The MINIFBQ FBQ800 features Behringer's FBQ Feedback Detection System that instantly reveals critical frequencies and can also be used as an audio analyzer. An additional low cut filter removes unwanted frequencies..."
.................
http://tinyurl.com/BehringerEQ
They've got these things in stock for about $50 at my local Guitar Center store. I'm an acoustic blues guitarist (by avocation), and I've been getting interested in getting my feet wet with computer-based home recording. So this EQ will no doubt have some future value to me beyond my FM transmitting activities.
I'll let y'all know how the clipping-elimination project works out.
That looks like a good choice. Better than what I suggested and less $. Hope it works to solve your problem. Keep us posted.
Neil
Been There, Done It
John