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Finally a decent FM signal


Gilrock
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Last year I tried the Whole Home Transmitter and never got it working much past my driveway even after trying the internal switch. So I ended up just using outdoor rock speakers that worked really well. This year I waited way too long to think about it. After getting some other new elements ordered in November I started thinking about improving my transmitter on Nov 27th this year. I searched a lot of posts on this forum which helped tremendously. I can't find the post that led me to buying an EDM transmitter but it was someone showing that they had shut down production for the year. I was disappointed because I had missed it by 4 days but I went to their website anyways. I convinced myself I wanted that one so I said what the heck I'll place an order and if it doesn't make it I'll use it next year. I get an email back asking if I realized they had shut down production for the year. I said yeah but it's the one I want so I figured I'd place the order and hope you had an extra one lying around. So then he sends another email and says well the only way to get one this year is I can send you one from our warranty stock but it will cost $20 more. I replied at lightning speed and said lets do it so 6 days later I had one in hand. I guess it pays to be optimistic and to talk nice.

And I guess it was because it was from warranty stock or something but it needed no assembly. It came with a power connector to solder on but I looked and it already had one and the chips were already installed. But don't tell anyone...don't wanna get them in trouble. :)

So I hook it up with the test antenna and I was disappointed. I had clear signal in the driveway but 100' across the street it had tons of static. I tried moving it closer to a front window and it only got slightly better. I tried moving the switch and it didn't get better at all. I later found in the manual that it was already in the 100 mW position before I tried moving it so I just made it worse moving it to the 10 mW position. In AZ a lot of our houses are stucco which is basically constructed with a bunch of chicken wire around the house which probably acts like a good shield for transmissions. I searched this forum again and decided the Ramsey TM100 mounted externally might be a good solution. I figured it was too late to buy one so I found a link one of you provided for making a clone of it. I didn't end up using the exact parts from that link but what I used is working great. Basically it's an FM Dipole antenna Catalog #: 42-2385 from Radio Shack for $9 soldered to an Indoor/Outdoor Matching Transformer Catalog #: 15-1140 from Radio Shack for $6. I mounted that inside 1" PVC to keep the antenna stretched out vertically and I ran 50' of coax (I believe RG-6) out to the antenna. I constructed it so that there is a 7' PVC pipe that holds it up in the air and I positioned it running up inside a tree and bungied the pipe to the trunk. It's working so well now I might need to turn it back to the 10 mW setting. It's clear for a few hundred feet but starts getting static after losing line of sight. The problem is that although it seems to end up with static not too far from the house I can go halfway across the neighborhood and still hear parts of the signal in the static so I don't know if it's enough to worry about it.

So then I went out and bought a second FM Dipole antenna to hook to my stereo so I can pick up my own transmission. I was using a second output from the PC but I like the idea of receiving my own FM signal as a means to monitor that it's working.

Yesterday I finished a home built frequency sign. That took way longer than I was expecting. Not sure what I hated the most...drilling 522 holes in 1/4" plywood or stuffing the leds into the holes.

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Using same radios (some are clear, and some there is whistling) how do they do receiving commercial stations?

I was going to suggest checking this too...I have found that on my Camry, my Christmas lights broadcast seems static-y if I'm not right in front of the house, but I also have trouble with more distant commercial stations in that car, too.

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in your search for FM Transmitters, did you happen to run into any threads on the FCC Part 15 rules and regulations? and 10mW would be the most I would push through that antenna

Edited by PMC
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I think tonight, I am going to play with the power output adjustment.

I do think it's an issue with the differences in sensitivity between the "Stock" Car stereo's and aftermarket car stereos.

The after market car stereo works great.

the "stock" car stereo's are the ones giving me trouble.

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I have my "transmitter" located outside in a shed, and the white wire you see is my antenna, I been broadcasting this way for 3 years now, The coverage area a solid block around the house, of course the secret is "modulation" have a good sound processor and that solves lots of issues, I recommend Breakaway Audio Enhancer

Edited by PMC
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in your search for FM Transmitters, did you happen to run into any threads on the FCC Part 15 rules and regulations? and 10mW would be the most I would push through that antenna

Yeah I think I read way more about that than I ever wanted to know. My impression is that we are all probably in violation of those regulations because if we weren't our signals wouldn't be clear 20 feet from the house. That's why folks that buy the transmitter that is supposedly compliant are always disappointed with the results. I moved the switch last night back to the 10mW position and the signal was still fine at the location 300' feet across a street that I wanted it to reach. I really couldn't tell much difference between the 2 switch positions. It seemed like when I lost line of sight of my antenna the signal degraded just as fast. I think I've done my best driving around to monitor the impact so I'm done worrying about it.

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Sorry to jack the thread.....On some FM stereos... I'm getting perfect reception, while on others, there is a lot of "whistling" and some static.

any ideas on what could be causing this?

You know what....I just found out that apparently my signal is only sounding perfect in my car. I had a friend of my wife watching and we told her to tune to the station and she complained it had a lot of static so I listened and it was sounding terrible. So then my wife says oh yeah it's not sounding good in my car either. So I go check and her mini-van sounds terrible. Then I double-check my car and it's crystal clear with no hint of static. I'm really not sure what I can do...I thought I had this behind me. I put it back to 100mW to test it and it didn't make a difference.

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Well I just tried a couple other frequencies. I originally was on 87.7. I tried 93.5 and it seemed worse. Then I tried 91.1 and it's sounding pretty good in both cars. I'm guessing my antenna length is better suited for that frequency. The calculations did show my center frequency was higher than 87.7 but the instructions for building the antenna made it sound like it had a big enough bandwidth that it could be sized for the center of the FM band and work for the entire band. I didn't want to cut the antenna I mounted which was 55" so that should have centered it closer to 90 instead of 98. Maybe changing the frequency will help you CrazyDave. Now I gotta rework my frequency sign before the contest tommorow night.

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You know what....I just found out that apparently my signal is only sounding perfect in my car. I had a friend of my wife watching and we told her to tune to the station and she complained it had a lot of static so I listened and it was sounding terrible. So then my wife says oh yeah it's not sounding good in my car either. So I go check and her mini-van sounds terrible. Then I double-check my car and it's crystal clear with no hint of static. I'm really not sure what I can do...I thought I had this behind me. I put it back to 100mW to test it and it didn't make a difference.

As PMC suggested, you're using a cheap antenna, meant for receive only, not transmit, and likely not anywhere close to a proper impedance match to your transmitter. Thats the crux of your problem.

There are much better options out there..not for 9.99, but just like the transmitters themselves, you get what you pay for.

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Guest Don Gillespie

I find some vehicles receive better signals than others, my truck gets great reception, where as my wifes Jeep sucks, it could be the vehicles that are the problem, most of our guests get great reception only one or two a night have static.

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As a sound engineer I agree with you. Does that program delay the audio at all? If it doesn't it's a steal at $30.

I been using Breakaway Audio Enhancer for my light shows for years, it's very low latency, its as real time as your going to get, and that $30 license you can install BAE on 2 other computers

The man that wrote the software is a Radio Processing Specialist and he writes his software so a DJ can listen in "real time" without any latency in the audio, the software has a 30 day free trial

Edited by PMC
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Well I just tried a couple other frequencies. I originally was on 87.7. I tried 93.5 and it seemed worse. Then I tried 91.1 and it's sounding pretty good in both cars. I'm guessing my antenna length is better suited for that frequency. The calculations did show my center frequency was higher than 87.7 but the instructions for building the antenna made it sound like it had a big enough bandwidth that it could be sized for the center of the FM band and work for the entire band. I didn't want to cut the antenna I mounted which was 55" so that should have centered it closer to 90 instead of 98. Maybe changing the frequency will help you CrazyDave. Now I gotta rework my frequency sign before the contest tommorow night.

First, turn off your transmitter go to your car radio and find a "clear" frequency, not just a frequency that doesn't have anything broadcasting on it, but a frequency that doesn't have any adjacency interference, so if you find say 91.3 is clear, make sure that 91.1 and 91.5 is clear too, here is a website that can give you some pointers, http://www.radio-locator.com/

As for your antenna, in the specs it should specify what wavelength you need to adjust for your frequency, never trust a "full bandwidth" setting, get it as close to your frequency as possible you just proved that theory yourself, if your antenna and FM transmitter is mis-matched, your creating nothing but RF noise and not to say your going to burn out your final in your transmitter, a mis-match means if you transmit 10mW almost 20% to 60% of that TPO (transmitter power output) is reflected back down to the transmitter

Go back to the factory antenna, move your transmitter as close to the light show as possible, install a sound processor, say the above mentioned Breakaway Audio Enhancer, set the sound to "eruption" and your Volume on BAE to -12 db you will be amazed with the results sound processing can do, with FM you can mask the static with sound/modulation, I should know I'm a radio engineer by profession

also, you will have to tweak your soundcard levels on your computer, and turning every pot/slider to full volume is going to distort the audio input for Breakaway Audio Enhancer,

make sure you set your computer levels to say 50% to start and work from there, in my world we have an expression "garbage in equals garbage out"

Edited by PMC
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Great Explantation PMC! Very helpful.

The one thing I am struggling with is peak deviation. What is a good average target value to hit?

For sound enhancement: after some poor audio at the beginning, I did pre-process all audios with am AirMax enhancer, a bit of EQ and some additional Stereo Width. That does save real time processing and at least the loudness is now the same for all songs...

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Anyone looking for a great antenna at a reasonable price:

This is a tunable quarter wave antenna with ground plane designed for transmission. The best part about it is the tuning capability, so if you have to change frequency you can easily adjust the length with a hex wrench to your new frequency.

http://www.fmdxantenna.com/proddetail.php?prod=14tun#.UM8m4Xy9KSM

Make sure you order the right adapters since it comes with a N-style connector.

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Great Explantation PMC! Very helpful.

The one thing I am struggling with is peak deviation. What is a good average target value to hit?

For sound enhancement: after some poor audio at the beginning, I did pre-process all audios with am AirMax enhancer, a bit of EQ and some additional Stereo Width. That does save real time processing and at least the loudness is now the same for all songs...

well, two things are you talking about frequency drift?

1) when the oscillator won't stay on frequency? if so.... then you need an oven to keep the chip warm, but, I would highly recommend PLL, that solves the issue cheaply and effeciently

2) Now if your talking about frequency seperation, in the good ole USA its peak devation of 75 kHz @ 200 kHz seperation

now your sound settings:

what you did is created ALC (Automatic Level Control) I never heard of AirMax, is it a rack mount chasis? or a plugin? also in the USA we have to set our pre-emphasis to 75 micro-seconds, but with a low power non-licensed transmitter, I wouldn't concern myself with it

My favorite (home) antenna is the Slim-Jim, you can built this antenna with parts from Home Depot or Lowes, and if you need to calculate it click here

Edited by PMC
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Thanks!

I was talking about the frequency separation. Thanks - now I vaguely remember - just wanted to figure out if it is better to keep the deviation closer to zero or closer to 75 kHz.

Since it is a digital controlled TX the PLL is locked fine - at least if I can believe the display.

Everything else is fine, and the sound is actually really great now. At the little power I am running I get no reflective power and I made sure all the other settings are compatible with US standards... I did bail on the RBDS this year - just did not have the time to get it set up... Something for next year...

I did all the sound processing in Pro Tools using plugins and it makes a huge difference. Since it is the same songs over and over it was the easiest way to do it.... I will still take a look at the BAE....

Edited by viennaxmas
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First, turn off your transmitter go to your car radio and find a "clear" frequency, not just a frequency that doesn't have anything broadcasting on it, but a frequency that doesn't have any adjacency interference, so if you find say 91.3 is clear, make sure that 91.1 and 91.5 is clear too, here is a website that can give you some pointers, http://www.radio-locator.com/

As for your antenna, in the specs it should specify what wavelength you need to adjust for your frequency, never trust a "full bandwidth" setting, get it as close to your frequency as possible you just proved that theory yourself, if your antenna and FM transmitter is mis-matched, your creating nothing but RF noise and not to say your going to burn out your final in your transmitter, a mis-match means if you transmit 10mW almost 20% to 60% of that TPO (transmitter power output) is reflected back down to the transmitter

Go back to the factory antenna, move your transmitter as close to the light show as possible, install a sound processor, say the above mentioned Breakaway Audio Enhancer, set the sound to "eruption" and your Volume on BAE to -12 db you will be amazed with the results sound processing can do, with FM you can mask the static with sound/modulation, I should know I'm a radio engineer by profession

also, you will have to tweak your soundcard levels on your computer, and turning every pot/slider to full volume is going to distort the audio input for Breakaway Audio Enhancer,

make sure you set your computer levels to say 50% to start and work from there, in my world we have an expression "garbage in equals garbage out"

Why would you tell me to go change everything after I tell you everything is working perfect now? The cars that had problems before have crystal clear reception now and even at 10mW I'm hearing it halfway across the neighborhood. Yeah I'm an engineer also so I understand your descriptions but I see no reason to tinker with it now that its working great. Before I started I did use the radio locator website and I sat in the car scanning the frequencies. I could not find any frequency that did not have some type of partial signal on an adjacent channel. But even though there is a real clear channel on 91.3 I don't hear any of my signal bleeding into it.

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Geez, you asked for help, right? Sorry we all made the effort.

And, for the record, still would not continue with that radio shack antenna long term..its not meant to be used as an antenna for an fm transmitter.

Yeah but once I say I got everything working I was surprised to see messages from you accusing me of having a cheap antenna that doesn't work well. I've already proved in the field it's working well. And if you read my original description I did use a matching transformer to mate up the antenna with the impedance of the coax which was matched up to the input called for by the EDM manual. To say my setup is not sufficient I think is misinformation to other potential users. Geez is right...this topic was dead days ago.

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Guest Don Gillespie

Some people are smarter than others, and require no help, you asked for help, you received help, you also received some very intelligent advice that might be worth listening to, but like I said some people are smarter than others.

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