jpjanze – Page 7

The text below is my answer to a recent inquiry from some one wanting to start a Part 15 AM. I decided to post it here. Now this is for a single site install. Multi sites require part 15 license free microwave or equalized phone line (avoid this option) and possibly synchronization or multiple frequencies.

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Hi,

I hope you don’t want to run on 700 using part 15. The results won’t be too good. As a general rule a successful part 15 needs two systems. You would run a intentional radiator on the “x” band 1600-1700khz. This would be your part 15.219 stick. Basically a 3m whip and a 100mw input to the final rf stage. A Rangemaster is well suited to this purpose and highly recommended. The processing you want to use with a Rangemaster is a Inovonics 235 3 band AGC / Asymmetrical limiter w/nrsc, a Optimod AM, or CRL SPP 800 followed by a SEP 800 with a SMP 900 or 950. This will modulate that Rangemaster to its full 95% negative and 125% positive modulation.

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Hi,

These do work as the manufacturer claims when set up properly. You want to mount that Hamilton Rangemaster on a 20-30ft copper 2 inch diameter pole above ground. Stick 8ft of mast in ground. Do not go any higher than thirty feet. You will just create extra aggravation in tuning TX and won’t gain much range. Next bond heavy gauge copper wire #6 solid from mast to 8ft copper ground rod. You want to bond all joints just as you would with a commercial tower. From the tip of mast to the Rangemaster you want #10 solid copper wire. For the radiator you want 3 meters of 1-inch diameter copper pole. This is the radiator and needs to be insulated from the mounting mast usually using PVC with appropriate reducers.

From the Rangemaster where the 102″ cb whip would normally mount you run a #10 stranded copper wire to the radiator. Put a copper cap on top of radiator to keep water out. Run your audio/power/metering lines from the Rangemaster down pole using standoffs. Put a snap on ferrite core where wire goes into Rangemaster. These lines will carry audio/power and volts/current monitoring into shack. On the shack end put another ferrite core on wire going into processors. From processors on is up to you. I recommend using only 100% genuine balanced line +4dbu equipment and ground everything.

This is what i am doing. Oh forget am stereo for part15.219. You just won’t get the phase info for the stereo to pass thru the hi “q” antenna system we use. You will only get stereo separation to about 800hz. Just a recap on processing. Asymmetrical limiting and nrsc filtering is a must. Carrier current i recommend lpb commercial broadcast transmitter not their carrier current version but the commercial broadcast part 73 TX. Better filtering, better sound, will stand up better over the years. Stay away from Radiosystems. They are garbage. Get a lpb line coupler. You’ll want to run the low end of the band usually 530 to 1000khz. I recommend stopping by the library on part15.us and reading up on carrier current. You will need a fim to properly set up carrier current(part15.219) and will get better results if you use the neutral loading as opposed to hot loading. You do not, repeat do not want to try and run the carrier current and the hamilton on the same frequencies using synchronization.

You will fall under the “composite system” regulations and they will ding you for excessive f/s. Now on the intentional radiator setup I described should pass. Most inspectors will let it pass unless they have a particular hard on for you or your station or just generally want you off the air. When they ask about your ground the wire from the tx to the tip of your mast is your ground wire for legal purposes. The mast is considered a supporting structure not a ground wire. Keep the instruction manual for the Hamilton handy to show the fcc guy. Make a photocopy of the Rangemaster cover showing the fcc id# and keep it in your station records along with the manual. Remember the metering lines i mentioned. Those run to your studio and i recommend keeping two separate analog volt meters out of an old transmitter hooked up to thes lines in your studio and keep watch and log your readings daily to prove compliance with part 15.219 power input requirements. Don’t forget there is a 1-2% drop in between readings at tx and readings in studio.

This power input is measured when the transmitter is not being modulated. Don’t worry if they go over when modulating the carrier. Also when you setup your studio wire it and setup equipment as if you have been doing engineering for 20+ years. If the FCC guy walks in and sees the studios looking like a pirate station than he will more than likely treat you as a pirate. Treat this as you are auditioning for a job. Now that is the way to do it right. If you just want to mess around on weekends and entertain yourself and not intending to reach an audience beyond yourself than you can forget all the above and stick a pole in the ground and put a CB whip on Hamilton and tune it up.

You probably won’t get bothered. However if you want to do it right follow the above. Although not needed, if you have access to one as a finishing touch get a eas decoder and logger. That will blow the FCC guys mind. I intend on getting one. Get a transmitter remote control too. I know this is a lot, but if you want to try and serve your community you need to treat it as if it was a licensed station. I will hang on to this message and send pic’s of my setup when I’m finished. I’m revamping everything to fall in line with what i explained above. And if you are really anal retentive and a perfectionist you can set your system up using a 10mhz dual trace shop type o-scope.

And I have not tried it out yet but http://www.radioassociates.com now makes a modulation monitor that measures positive and negative modulation. It supposedly will work with the peanut f/s we use. Forget using a belar modulation monitor or similar. They do not work with less than 5v of signal and require closer to 10v.(been there tried that). That is all the info i can offer. I recommend you run an underserved format on your station and get involved in your community as much as possible. We will be doing remotes, etc. I’ve got a sph-3a hybrid and access to a mini board for remotes 🙂

Thank you,

Rev. Robert p. Chrysafis
Universal life ministries (ulc)
Http://www.ulc.org

Moderator hunterdonfree
Http://groups.yahoo.com/groups/hunterdonfree

Here is a Updated list of ideas for a Part 15 AM Transmitter kit Design. the fact that people pay $1k for a crystal controlled transmitter, makes me think a kit like this would sell great…

1) Modulation should be capable of 100% Negative and 150% Positive Modulation

2) Unit should be 2 peice with a Modulator in one and the RF Deck in a Pole mounted sealed housing

3) Output should be 50 ohms

4) Final should be switchable between 100mw and 1 watt input levels

5) Final RF components should be rated for 5 watts
to make the final RF stage indestructable from high VSWR.

6) Modulator should be Class “A” with the final RF being Class “E” output

7) Transmitter should include a built in output tuning meter to aid in tuning antenna.

8) Transmitter should employ a Dual loop PLL w/TCXO

9) Audio input should be 600 Balanced +4dbm and RCA unbalanced -10mv and should be transformerless

10) Audio response should be from 10 to 10,000Hz, with the ability to pass low frequency square waves with no tilt or overshoot

11) Audio and power leads should employ ferrite beads to keep studio lines from being least resistance to ground

12) Two ground options should be available. one sized to #10 and #8 lugs

13) Power supply should be filtered in the unit itself and include onboard regulation and filtering and power input should be 110v 3 prong grounded plug like found on computer power supplies. unit should also have filtered 12Vdc input as well.

14) Transmitter should be synchronizable

15) Unit should be a kit and cost no more than $400.00
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By Rev. Robert P. Chrysafis

Hobby Broadcaster Given Temporary License

Part 15 AM Transmitter Site Plan

Doing a Part 15 AM the Right Way

Updated Ideas for would be kit designers