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FTL_Ian

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Being a good radio neighbor!
« on: January 26, 2010, 11:04:52 PM »

If you want to lower the chances of an FCC raid, you need to make sure you're being a good neighbor to your fellow broadcasters.

1.  Pick an open frequency.  Here's a handy tool that makes it pretty easy for the FM band:  http://radio-locator.com/cgi-bin/vacant .  Once you've found a frequency, you may want to drive around just to verify it's clean.  "Stepping" on an existing broadcaster is a sure way to get a visit from the FCC.  Treat your fellow broadcasters as you would like to be treated!

2.  Make sure that you are running a low-pass filter!  This prevents your transmitter from splattering itself all over different frequency multiples via "Harmonics".  Meaning, if you are operating a cheapie transmitter with no low-pass filter at 100MHz, then you are also broadcasting at 200MHz, 400MHz, and so on.  This is NOT being a good neighbor, and you may be interfering with other communications on other bands even though 100MHz might have been a clear channel.

3.  Make sure you aren't bleeding RF interference into your neighbors' televisions and radios.  (I'd like some more engineering minds to chime in on how to ensure this without necessarily announcing to your neighbors what you are up to.)

Am I missing something?
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KDus

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Re: Being a good radio neighbor!
« Reply #1 on: January 27, 2010, 01:46:05 AM »

If you use an amplifier, you can use a filter before AND after the amp to be as clean as possible. You don't want to waste power amplifying RF that you are going to throw away anyway. The amplifier it self can actually create harmonics and oscillations we call "birdies". So, a filter after the amp is vital.

 Don't over modulate. If the meter shows you're at %105, trust it. Unless you spent thousands of dollars on audio processing, don't expect to sound as loud and strong as the commercial stations. To get that loud on the dial, you'd probably have to deviate (modulate) way past the channel edges and bleed into adjacent channels. Don't presume that peaking and tweaking is making your amp more powerful. If you go messing with the tuning of your amp or filter, you could be creating oscillations or non-linearities that are introducing AM noise into your signal. Your meter might show more power, but it could be that the extra 2 watts is a horrible whilstle being blasted into an aircraft band.

AM amplifiers need to be linear. If you're pushing your amp into clipping or into a non-linear area, you're are probably splattering all over the dial. With AM, you also need to be concerned about the harmonics below your carrier. AM puts the RF in side bands above and below the carrier. So, if you're clipping your amp and creating crap you can't even hear, it's creating side bands above and below your channel. In the AM spectrum, Your inaudible noise 20kHz below your carrier could be squashing some guys coast-to-coast reception, 50 miles away.

Beyond that, use the least power possible. Find a higher gain antenna and reduce your power. Coil up any extra feed line coax so it will act as a choke. Look at ham web sites about coax chokes.
« Last Edit: June 13, 2010, 01:44:47 AM by KDus »
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KDus

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Re: Being a good radio neighbor!
« Reply #2 on: June 13, 2010, 01:43:55 AM »

Coil up any extra feed line coax so it will act as a choke. Look at ham web sites about coax chokes.
Today I figured out I'm losing about half my power in the coil of spare feed line. I'll report back when I figure out a good feedline choke model. I found a program online that I'm playing with #of turns. diameter and length. So far, it looks like about 2 turns around 10" will help suppress the second harmonic, but there will be a little loss.
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Re: Being a good radio neighbor!
« Reply #3 on: September 04, 2010, 09:23:39 AM »

3.  Make sure you aren't bleeding RF interference into your neighbors' televisions and radios.  (I'd like some more engineering minds to chime in on how to ensure this without necessarily announcing to your neighbors what you are up to.)

Best way to do this is by casual conversation about how nice their yard looks then ask if they have been getting noise or interference on their tv's or radios like you have been. This gives the neighbor a sense that your just trying to find out if tv or radio in the area is being interfered with, or that your tv and radio need to visit the junk yard.

The double filter option works extremely well. Making them is easy and there are schematics all over the web to various filter designs. I have made several in-line 7 pole filters out of copper pipe and hose clamps.

A quick and easy filter can be made by taking lengths of coax cut to 1/8 wavelength of the interfering frequency and attached through a T fitting 1/8 wavelength from the TX output connector. Continue down the line for each frequency harmonic you want to null out.

At the end of each notch (cut 1/8 wavelength coax), leave about an extra inch or so of center conductor at the end as well as enough of the ground braid to extend completely over the center conductor. This will allow for peaking of each notch coax. Spectrum analyzer is useful for this, or a general scanner/receiver with an S meter to aid in reducing each harmonic.

RFB

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TimeLady Victorious

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Re: Being a good radio neighbor!
« Reply #4 on: September 04, 2010, 10:39:56 PM »

Would TV interference really happen that much now that DTV has arrived?

You may thank the federal government for imposing digital TV, which is less robust than analog, on people by the way.
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Re: Being a good radio neighbor!
« Reply #5 on: September 04, 2010, 11:30:09 PM »

Would TV interference really happen that much now that DTV has arrived?

You may thank the federal government for imposing digital TV, which is less robust than analog, on people by the way.

As a matter of fact..even more so. Why? Because the transmission power level of digital television is as much as 1/2 less than an analog transmission.

If someone is operating a transmitter without proper filtering, the interference can easily cause someone's DTV receiver box or DTV ready television to simply freeze, or produce missing data chunks, which is seen on the screen as black pixel boxes or distorted pixel boxes.

DTV has the same transmission bandwidth as the analog system. Aprox. 6Mhz wide. In DTV...there is a "Pilot Carrier" at the low end of that 6Mhz bandwidth signal. The rest of the bandwidth is occupied by the data. It is in there where the video/audio/info is located.

Any signal interference within that 6Mhz chunk of spectrum will cause errors to the data stream being received, producing the effects stated above. Like trying to watch a video stream or audio stream on a bad internet connection with a lot of packet loss.

Filtering should be EVERY operator's priority!!! After all....it was careless operating practices and piss ass poor engineering practices that brought us our lovely friends called the FCC back in the hey day. Their primary goal was to "clean" the radio spectrum because so many radio experimenters were purposely causing interference or operating in worst case/bad taste ways.

There is a very neat tool that anyone can use to help aid in keeping their operations technically up to spec, and even exceeding those "big boys" signals. Its called "Google" and one could begin to clean up their signals by simply typing in "FM low pass filters" or "harmonic filters" or any other related keyword. Tons upon tons of plans, schematics, tips and do's and don't advice on the web. :)

RFB
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Puke

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Re: Being a good radio neighbor!
« Reply #6 on: September 05, 2010, 08:03:21 AM »

Don't forget to bitch and moan like a little pussy to the free stream provider / podcasters when they use adult language.
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KDus

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Re: Being a good radio neighbor!
« Reply #7 on: September 09, 2010, 06:49:58 PM »

Spectrum analyzer is useful for this,                             RFB

I've seen them as low as $100 on ebay.
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RFBurns

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Re: Being a good radio neighbor!
« Reply #8 on: September 23, 2010, 10:25:47 AM »

I have not run across any at that low price yet, but ebay is an excellent source for spectrum analyzers. I managed to obtain an HP 8590A and a Motorola 2050D (number hard to see on back label) communications analyzer that has so many bells and whistles, but its best feature is the modulation monitor and measuring functions.

Some may consider having a spec an may be overkill for most operators since many of the pre-built transmitters and transmitter kits have pretty good filtering. However all it takes is a spot of rust on antenna elements or bad connectors to muck up that stock filtering...and before you know it....KNOCK KNOCK..someone's at the door!

And of course...how is one to know their equipment is spitting out a harmonic making the entire neighborhood's DTV's freeze up and pixel in the upper VHF band..or worse...jam up crucial aircraft navigation/beacon systems.

Using simple scanners can help and is an alternative..one only need to know the harmonics from the fundamental and simply tune to the harmonics and note signal strengths if the scanner has a signal strength indicator.

However to ensure a proper reading using either a spec-an or a scanner is to tap the signal output at the transmitter output point. A simple T fitting and attenuators, an effective coupler can be built and used to constantly monitor the signal output. If there is an external filter being used, simply put the coupler at the output of the filter.

Believe it or not....having such a monitoring system online and ready to show "proof of performance" earns points with a visiting FCC inspector to a Part 15 installation. It shows them that you are taking real steps to make sure your not causing interference. And it is exactly how high powered licensed stations check their signals before those signals hit the antenna system.

For AM installations where the TX is outside and some distance from the studio, a simple pick-up coil connected to some spare feed line and isolated from any physical connection to the TX or its power/audio cabling, makes a very effective "tap" to monitor your Part 15 AM signal. Or one could get creative and use some of that empty space inside those Part 15 transmitters and place the tap coil inside next to or loosely wound around the short antenna connecting wire. Do not couple too closely or make a direct connection because this will dampen that tiny 100mw signal and make peak tuning a nightmare!

And for those who like to push the power past the Part 15 mph speed limit, incorporating such a monitoring system can add a measure of relief to worry about jamming up other bands and help eliminate the potentials for interference complaints.

Plus...regardless if the setup is a compliant Part 15 or a pirate flame thrower, it is just good and proper engineering practice to know exactly what your signal is doing, both inside intended band and outside of intended band.

A few "good" sense practices can go a long way to saving your butt and your station.


RFB
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Kuerno

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Re: Being a good radio neighbor!
« Reply #9 on: November 30, 2010, 11:33:31 PM »

Would TV interference really happen that much now that DTV has arrived?

You may thank the federal government for imposing digital TV, which is less robust than analog, on people by the way.

As a matter of fact..even more so. Why? Because the transmission power level of digital television is as much as 1/2 less than an analog transmission.

If someone is operating a transmitter without proper filtering, the interference can easily cause someone's DTV receiver box or DTV ready television to simply freeze, or produce missing data chunks, which is seen on the screen as black pixel boxes or distorted pixel boxes.

DTV has the same transmission bandwidth as the analog system. Aprox. 6Mhz wide. In DTV...there is a "Pilot Carrier" at the low end of that 6Mhz bandwidth signal. The rest of the bandwidth is occupied by the data. It is in there where the video/audio/info is located.

Any signal interference within that 6Mhz chunk of spectrum will cause errors to the data stream being received, producing the effects stated above. Like trying to watch a video stream or audio stream on a bad internet connection with a lot of packet loss.

Filtering should be EVERY operator's priority!!! After all....it was careless operating practices and piss ass poor engineering practices that brought us our lovely friends called the FCC back in the hey day. Their primary goal was to "clean" the radio spectrum because so many radio experimenters were purposely causing interference or operating in worst case/bad taste ways.

There is a very neat tool that anyone can use to help aid in keeping their operations technically up to spec, and even exceeding those "big boys" signals. Its called "Google" and one could begin to clean up their signals by simply typing in "FM low pass filters" or "harmonic filters" or any other related keyword. Tons upon tons of plans, schematics, tips and do's and don't advice on the web. :)

RFB

FWIW - I personally have way less trouble with TVI now that things have gone digital.  Even with high power HF including upper HF 10&11 meters as well as my little FM micro I now have no trace of what I am doing on TV and that's in a TV "deep-Fringe" area with my DB4 mounted right underneath the ground radials of my A-99.

I also agree with Puke to some extent.  That was one of the reason I have dropped Oracle off my micro.  It's hard enough to stay on the air, I don't need help pissing off my neighbors with the never ending barrage of F-Bombs out here in the middle of Utah.
« Last Edit: December 01, 2010, 12:18:12 AM by Kuerno »
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KDus

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Re: Being a good radio neighbor!
« Reply #10 on: January 18, 2011, 12:06:05 AM »

Last time I was in UT, I heard something freedom oriented, I think it was called family round table radio. I listen for pirates when I travel.....
I set up some pirates (FM) in Orem, Provo, and AF. The Provo stick was visible from the 15 and could be heard from south Santaquin to past Lehi with about 9 watts. It was perfect.

L.A. has worse reception with DTV. The word on the street is that multipath is a bigger problem than expected with the lower power levels, and tall buildings. I see pixelation and frame loss effects. I don't know if TV uses equal sidebands but I do know that FM is playing with the idea because adjacent channel interference is worse than expected.
So, we could end up with even lower power on one sideband for the IBOC carriers on FM.

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Re: Being a good radio neighbor!
« Reply #11 on: January 25, 2011, 03:47:19 AM »

Don't forget to bitch and moan like a little pussy to the free stream provider / podcasters when they use adult language.


If listeners of licensed radio tuned in more often to net radio, they would become acclimated and there be less little wussy moaning and groaning.
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humpower

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Re: Being a good radio neighbor!
« Reply #12 on: February 19, 2014, 12:04:09 AM »

Would TV interference really happen that much now that DTV has arrived?

You may thank the federal government for imposing digital TV, which is less robust than analog, on people by the way.

The interference of DTV is much less, so let's why government choose to develop digital broadcasting, and it can carry more channels.
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