Post by computerdoc4751 on Jan 10, 2013 21:09:14 GMT -6
I just got a CZH-15. I live about 3 miles from a small town airport. Has anyone had problems with spurious emissions in the Aircraft band? I'm a FCC licensed tech, also have an Amateur license, so wouldn't be a problem to construct a good filter. Has anyone had any luck with a notch filter that would cover about 3-5MHZ of the FM band?? or should I just go with a different location about 10 miles from the airport??
You should use a 7 pole or at the bare minimal a 5 pole low pass filter. As I am sure you have read elsewhere those Chinese transmitters are notorious for putting out spurs and harmonics since they're usually not built to the high quality standards that are enforced over here. You could use a band pass filter but it's not all that necessary as most of the communications you have to worry about interfering with are above the FM broadcast band and also most of the harmonic/spur issues tend to happen above, not below your FM frequency of use. I believe you are confusing a notch filter with that of a band pass filter. Any good filter should start rolling off spurious emissions above your broadcast frequency; starting below 108MHz.
You should keep in mind that if you're a ham radio operator that doesn't mean anything to the FCC if your caught running a radio transmitter outside of the frequencies your ham license allows you to use. Obviously this makes you a pirate radio operator if using higher power than allowed by Part 15 specifications without the proper broadcast licensing and if caught they could revoke your ham license. It doesn't always happen, but it's not unheard of either so I wouldn't go telling everyone you're a ham in hopes that it somehow will get you out of any sort of trouble. I don't mean to sound harsh but it's best to be informed.
Post by computerdoc4751 on Jan 12, 2013 12:08:18 GMT -6
Yea, I know. If anything, it might get me harsher treatment cause I'm a Ham and "should know better" Information on that transmitter says that it has a LPF built in, that self destructs in a matter of hours because of the cheap components. Any point to replacing the SMT components with ones with the proper specs? I have the skill and equipment to replace them. I also think it wise to go with the location 10 miles from the airport, and stream the signal from here to there.
I ran a czh 7 watt for two years near our airport without a problem but as soon as I turned on my new transmitter (100 WATTS!!) Industry Canada came knocking with concerns about being so close to the airport. If I stayed with my 7 watts they would not have know I was here... sixer
I ran a czh 7 watt for two years near our airport without a problem but as soon as I turned on my new transmitter (100 WATTS!!) Industry Canada came knocking with concerns about being so close to the airport. If I stayed with my 7 watts they would not have know I was here... sixer
That's how it happens man. You operate under very low power initially and then want more to increase your reach because you figure the coast is clear and you have it in your head that nobody cares anyways. ;D
Then Industry Canada knocks on your door...
Hey everyone, I'm Sam from western Canada and I am another fellow pirate. I also have some experience with regulators up here. Like sixer's experience, the guys were super cool about everything. They just said you can't do it anymore and rambled off the reasons why, like interference with aviation and the standard spiel. (I'm about 40 km from a major airport)
When I first launched my last station prior to shut down, I started at 1 watt on FM. I had a relatively decent setup at the time too. I had a very clean signal from a well-built transmitter with proper filtering, a 5/8 wave antenna perfectly tuned with around 3.5dBi gain.
But after a while...isn’t just wasn't good enough! lol So I ordered a 30 watt amplifier. It wasn’t long after that, I had inspectors at my door. All because someone caught the signal at a distance and didn’t like the ‘rap music’ I was playing. I know to this very day, that if I had just stayed at 1 watt, I’d most likely still be operating at that power under the radar.
There's been this notion out there in pirate radio land that Canada is this safe haven for pirate radio. However, let me tell you that in recent years, they've been cracking down. Two other pirates in my area have been silenced recently. I know one of them personally and he lasted for 3 days at 10 watts before he had inspectors at the door! No joke.
My theory is that because the massive number of relatively cheap, high powered LPFM transmitters that have flooded the market from China, there is an ever increasing number of people setting up low powered stations and this is keeping inspectors busy. Traditionally in Canada, Industry Canada doesn’t go out looking for pirates to nail, but they do act upon any complaints or reports of unlicensed activity. I figure that as this hobby becomes a lot more affordable and with the increased number of FM transmitters out there, IC may be more on the look-out now. Just a theory of mine.
On your first offence, provided that you co-operate immediately and don’t behave like an ass, you're off pretty much scot free. Second time around, expect at the very least a fine.
Also, not to pick on Ham operators, but look out for them in your area. They’re easy to spot as there’s usually a tower in their backyard or at the very least, an antenna stack on their roof. If you know there’s one in your area, then you really need to be careful as they will report you if they stumble upon your signal. (All the more reason to really make sure your signal is clean) In all fairness to them through, it’s not the easiest thing in the world to get that license and there is a heavy technical requirement, so they take real exception to pirates like us that sort of come along for the free ride.
Anyways, glad to be here and I look forward to getting to know you guys.
Post by computerdoc4751 on Jan 18, 2013 5:53:09 GMT -6
Actually, I am a Ham. I got my Extra last Oct. I also got my A+ certification in 2012. Not bad for a 56 yr old guy!! I've held a 1st class radiotelephone license w/Radar endorsement , which was later changed to a lifetime General, since 1978. I've been a "Radio Man" almost my entire adult life. I originally wanted to be "on the radio" but found out quickly that if you want to be in front of a Mic or Camera, you had to know someone. So, my 1st pirate station was 1 watt 0n 570 AM. we were 1/4 mile from the high school, so we had plenty of listeners. Out in the middle of nowhere, no one bothered us. I spent the next 35 years working on repeaters, transmitters, and Cell towers, out in the field.(IOWA SUCKS IN WINTER, FLORIDA IS GREAT) I always wanted to start another station, so here I go... I am in small town, gotta keep a low profile. I think I have the knowledge to keep the FCC a couple of steps behind..... or at least chasing their tails a while! I researched the frequencies the local Airport uses, and since the cheap Chinese transmitters put out a strong spurious spike 20MHz above and below the set frequency, I chose frequencies that left a wide space.. I'm going to try to just blend in to the crap they call classic rock, without all the advertisements...thats the real reason, I think. The commercial stations now play 20 minutes of commercials EVERY HOUR. Thats bullshit. Right now the audio is streamed over a shoutcast server set to private, to the transmitter at another location. It's on a connection that can't be traced. We are thinking of adding a couple more transmitters to our "network"
Contact Brian at vielectronics@yahoo.com. He hand crafts every filter he sells and can deliver up to -80db attenuation of those nasty harmonics.
Another thing to watch for with those CZH units is their frequency spec. Usually they are NOT on frequency!! Adding a 3-30pf trimmer cap to one side of the crystal can "bend" it on frequency where it needs to be.
Primary issue with some of those CZH units are the fact they use mass produced components which do not have very good tolerances and will drift over a short period of time, which can be accelerated by excess heat buildup in the cabinets, particularly with the higher powered units..ie 7 watts and up. Increase the ventilation and use a better fan will help.
Not only is the harmonics and frequency of a concern, but also inter-stage spur is produced after a time. Crack open the case and unsolder the metal shield and you will see the stages and their tuning components used. Most use the small variable inductors but there are a few with a combination of both variable inductors and variable caps. Simply re-tweaking them can eliminate the inter-stage spur issues.
There is also some room on-board to add extra filtering capability. On the underside of the PC board in the final low pass filter section are SMT chip caps. Replace these dumb things with small variable caps of 3-30pf types. I used the SMT variable caps so the board will fit back into the cabinet, and drilled access holes on the bottom for these as well as the "bending" variable cap for the crystal. This way you can tune up and peak and tweak with the whole unit inside it's metal cabinet. If you tune outside of the cabinet and re-insert the board into the cabinet, it will throw off that tuning!!
Another helpful thing to do is to make sure the mounting holes on the PC board underside are clean and clear of flux and have a good metal to metal contact with the mounting screw studs so as to ensure good grounding of the PC board to the cabinet for maximum shielding, and this will help a great deal in minimizing the inter-stage spur problem too.
And of course, a spectrum analyzer is very handy to have around when performing these adjustments!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Post by computerdoc4751 on Jan 23, 2013 7:14:30 GMT -6
Thanks for some very good info! Actually I'm in the process of building a LPF tuned to our frequency. Found a design that is fairly easy to build and tweak. I've got extra time on my hands, anyway. I got the 15 watt transmitter, and I was actually impressed with the sound-and it was dead on frequency! Anyway, it sounded great on tests, when we were checking coverage, we were getting around 4-5 miles solid coverage in a medium size town. When I started out the 2nd day of tests, after moving the antenna 25 feet higher, I noticed we were barely getting 5 blocks. Checked the transmitter, putting out 1.4 watts. probably running off the driver. It turns out that the RD15HVF1 output transistor is being run at just about its upper limit. It ran pretty warm on the 2 watt setting, I think its just being ran so hard, any little problem with the antenna or coax will wipe it out. I emailed the factory in China, and he told me that most of the cheap antennas being sold are really hard to set up properly, and if you don't have a SWR meter to check it, you'll probably end up blowing the final. I used a piece of cable that turned out to be 75 ohm cable instead of 50.... Anyway, he's sending replacement finals and information on how to upgrade some components and add more shielding. I'll pass the info along when I get it.
I just got a CZH-15. I live about 3 miles from a small town airport. Has anyone had problems with spurious emissions in the Aircraft band? I'm a FCC licensed tech, also have an Amateur license, so wouldn't be a problem to construct a good filter. Has anyone had any luck with a notch filter that would cover about 3-5MHZ of the FM band?? or should I just go with a different location about 10 miles from the airport??
Have you thought about borrowing a spectrum analyzer? Have you checked to see if the Tower is anywhere near the bands in 108mhz or a bit higher? I know for a fact that ALL of the CZH interfere with Analog TV channel's pictures 3-5 or 3-6. 3 miles on that band at 15 watts is very risky! Here is a recent true story where a man is fined $20,000 for same thing basically. FCC Sues Man After His Pirate Radio Broadcast Interferes with Airport Tower I wouldn't run anymore than 7 watts or so being that close.
Now you could do one of several things going backwards. Taking a trip to the tower and talking to them about how your a mile (not 3) doing a Part 15 at friends house. You give them your # and 'name' of cellphone to call you in case of issues. During your first visit they will likely know if they had problems. make sure your Transmitter is ON before you go there. This way you can listen to the tower as you discuss your concern(s).
So if the weather , equipment issues etc suddenly DOES arise causing interference they will call YOU- not the FCC. Which in turn would investigate, find you and warn/fine you. So after all is said and done- make a tight 88-108 filter. After your visit- then YOU decide if you must move, lower your power, change your antenna etc.
I got the 15 watt transmitter, and I was actually impressed with the sound-and it was dead on frequency!
One in about 20 units will be pretty darn close to "dead on" frequency. The worst I found was off by about 18Khz. The best was about 45hz from center frequency. To me even 45hz is not acceptable so I padded that crystal in that unit as well.
When I started out the 2nd day of tests, after moving the antenna 25 feet higher, I noticed we were barely getting 5 blocks. Checked the transmitter, putting out 1.4 watts. probably running off the driver. It turns out that the RD15HVF1 output transistor is being run at just about its upper limit. It ran pretty warm on the 2 watt setting, I think its just being ran so hard, any little problem with the antenna or coax will wipe it out. I emailed the factory in China, and he told me that most of the cheap antennas being sold are really hard to set up properly, and if you don't have a SWR meter to check it, you'll probably end up blowing the final. I used a piece of cable that turned out to be 75 ohm cable instead of 50.... Anyway, he's sending replacement finals and information on how to upgrade some components and add more shielding. I'll pass the info along when I get it.
Any system operating above 3 watts must have it's antenna properly tuned and use good low loss coax. Yes a VSWR meter is a must just as is having the extra low pass filtering. I'm interested in the info from the mfg on the component changes and extra shielding, though my units are already "beefed" up in the areas of common problem. Never had the stock RF finals go bad on me, probably because I never let them operate "stock" even before first power on. The very first unit I purchased some years ago I had operating on the bench connected up to just about every piece of test gear you can think of. Looked like a patient on a hospital bed! After putting that first unit through modifications, I decided that any further units purchased will also go through the "Dr. Improve" checkup and fitting.
They do have excellent audio performance and very good separation. The 1415 chip is very well designed internally and Rhom learned a few lessons from their previous FM chip, which was plagued with internal noise and isolation problems. Most of those CZH/FMUser/HILLY units make great exciters, again adding the necessary mods to make them ship shape for long term stability. I even used one (CZH-20) unit to sub for a blown up Crown exciter on a licensed FM which was pushing a Harris FM-20K cabinet. The manager of the station never heard the station sound so good before but had to ruin the party because it's not legal to use any non FCC Part 73 certified unit in the transmission chain, though emergency situations does allow for a little wiggle room to restore on air status.
As to the airport interference situation. Voice comm frequencies are from 108Mhz to 118Mhz and use AM modulation...ironically. The thing to worry about is iner-mod mixing and IF frequency spacing, especially when within a couple miles form an airport communications array, which most of those will be located somewhere on the airport property either on top of the control tower, or on a short tower stack in the middle of the airfield. But the thing I would take into consideration the most is the approach and departure paths as well as the holding pattern zones. It is these 3 areas that you should really try to avoid causing interference with.
While your building your low pass filter, you should also build an in-band, on frequency notch filter for the spectrum analyzer. This is simply a frequency notching filter built or tuned for your operating frequency so you can notch out the main carrier on the spec-an and increase the gain of the spec-an to look for those spurs and inter-mod ghost signals without overloading the spec-an. Measure in two ways, one is to sample at the output connection going to the coax, the second is to use a 1/4 wave tuned and matched dipole antenna directly to the spec-an and measure some distance form the TX antenna point, say about 1Km. Again use the notch filter at the distance measurement point and up the gain on the spec-an. Measure with no modulation, and then with modulation comprising of 3 specific test tones...400hz, 1Khz and 10Khz. The 10Khz test tone will reveal any high frequency "splatter" being produced by the transmitter. Run tones at 3 different levels each. -10db, -5db and then at 0db, no processing inline. If all 3 tones and 3 levels indicate clean operation, your good to go!
One more very important note. the BH1415 chip, though very good in design and performance, DOES produce a small amount of AM artifact modulation from the L-R sub-carrier. Unfortunately there is no way to adjust the 38Khz sub-carrier null as that is internal to the chip. But there is an adjustment for the 19Khz pilot level injection on pin 19. This adjustment is done by placing a capacitor from pin 19 to ground. If pin 19 is left open, the pilot level is WAY above 10%. If you have too much pilot level going out, that will increase the AM modulation artifact and stir up all kinds of AM byproduct including dampening the quality of sound on the FM side. I used a 25pf cap and brought that pilot level down to +/- 9.85%, which helped to eliminate the AM junk out of the composite and improve separation and frequency response.
Good luck and keep us all updated!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Post by computerdoc4751 on Jun 19, 2013 6:50:59 GMT -6
Well, here it is june, and still crankin' the damn thing. Added a mixer that isn't a computer, discovered that these units sound and work great if you keep the modulation at 90% tops. The volume is a little lower compared to other stations, but sound quality is excellent. Over modulating this FM transmitter creates all kinds of splatter and spurious signals and actually reduces overall power (and range). I've tried software limiting on the media players (I use 2 computers playing MP3's) and it helps, but not as much as running it through a XENYX mixer/limiter before the transmitter! So far, no letters from the FCC. We have a small base of listeners, and the closest station on our freq is 95 miles away, so probably won't get any complaints. I built a 1/4 wave GP antenna it's concealed in an attic, we get 7 miles in some directions (flat open land) and about 3 towards the downtown area. Been on 7 months now! don't keep a regular schedule, but usually on from 4am-10pm If anyone is considering buying the CZH15, it is a good transmitter, but it won't last a day at full power unless you drill ventilation holes in the top cover and add a 3-4" fan blowing in. Leave the original tiny fan in place to help pull air thru the unit. I've run this unit for 72 hours nonstop, and with the added cooling, the internal temp never went past 31c which is excellent.
When I first launched my last station prior to shut down, I started at 1 watt on FM. I had a relatively decent setup at the time too. I had a very clean signal from a well-built transmitter with proper filtering, a 5/8 wave antenna perfectly tuned with around 3.5dBi gain. I know to this very day, that if I had just stayed at 1 watt, I’d most likely still be operating at that power under the radar.
Welcome Sam; Hey you're talking about me! I remained to starred to ever upgrade from my 2000 era NRG 1-watter VFO - she's humble but provides a nice signal to noise and good stereo sep. (figured out how to cancel signal drift - let warm up for 20 minutes and have a sliding plate 3 ins over the PCB, if she drifts. but Steve's stuff was so good drift really was never much of a problem (only huge humidity or cold fronts would make me have to adjust my rigged slider plate. FM PC is down last couple of years ;-/.
I'm looking into TV now.............;-) - alot more $$, time and work to setup programing.
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