I wonder if anyone in the group has constructed one of these little kits? I would be very interested to hear opinions as to how easy it is to put together and whether there is much soldering involved (it is shown as a simple skill kit). Any help and opinions as to the sound quality and distance coverable within Part 15 would be gratefully received, thanks.

Has anyone tried one of these outfits?

http://www.radioassociates.com/

I'm intrigued.  It appears it can be used with NO connection to the feedline for Part 15, hence wasting no prescious power. The only reviews I can find are from hams who all seem to love it.   I do have the ability to test one vs a Belar in a commercial radio setting, but maybe someone has tried one?

As modulation is very critical to sound and coverage we need a good way to determine that we're putting out what we can. I've noticed that just a slight adjustment to lower volume (hence lower modulation) makes a noticeable difference in coverage area and clarity of signal.  But how far can we go before distortion moves in?  It's hard to determine just listening on a radio. The quality of the radio is so much a determining factor. I'm hoping this device/computer setup might give us an accurate gauge to determine modulation.

Tim in Bovey

About 1:38 into the video:

http://www.youtube.com/watch?v=9VQJHMLYOU4

Those of you not into technical stuff might find this boring, but I share it here for my fellow tech/engineer types who might enjoy reading of the troubleshooting and repair of a transmitter.

I recently picked up a couple of AM-30 transmitters on eBay. One was in near-mint condition, super clean inside and out. It was as if it had never been used except there was a lead connected to the input terminals. Perhaps it was operated once to test, and then reserved as a backup/spare? Anyhow, I connected it to a dummy load and an audio source and powered it up. It put out its rated power and sounds good. SCORE!

The other AM-30 was a different story. I considered that it might have a problem from the photos as the AC line fuse was missing, but I took a chance anyway.

Right off the bat it looked like someone had replaced the voltage regulator transistor. Upon closer investigation, I saw that the insulating washer (which isolates the transistor tab, which is connected to the collector and is at power supply potential, from the chassis) had been omitted. Perhaps it would be that simple? Nope. Further inspection revealed that the wires for the emitter and base had been crossed. The previous 'technician' (who didn't know how to properly mount the device) apparently was trying to install it as shown in the schematic, which, BTW, is incorrect. In fact, having three leads, there are exactly three ways to connect a transistor. There is the correct way, which is not too difficult for someone familiar with basic power supply circuits to determine. There is the incorrect way shown in the schematic. And this one was connected in the remaining, also incorrect way.

Surprisingly, the transistor survived the incorrect wiring unscathed, but there remained a dead short in the power supply. That turned out to be a shorted bridge rectifier. I just happened to have one around.

With the bridge replaced, it no longer blew the fuse. Power supply voltages seemed reasonable, and it made RF. As I slowly increased the power, though, the power supply voltage began to sag and I began to notice quite a bit of hum, which got worse as I increased the power. At about half-power the audio began to get severely distorted.

Have you guessed yet? It was the main electrolytic filter capacitor for the 30-volt supply. Possibly just dry from age, or maybe stressed from the shorted bridge (the safety vent looks like it may have let some of the Magic Smoke escape at least once). 

In any case, I sumped it with a good one and now the voltage holds steady and teh signal is clean -- free of hum and distortion, even a full power. YAY!

Still has a minor niggle or two - the on-board meter works for power output, but not for audio level. That needs looked into, but even if unrepairable is only a minor inconvenience.

I'd have probably been disappointed had I paid the asking price, but for what I actually paid via "Make Offer" I guess I did OK, and it's always rewarding to successfully repair something and return it to useful service.

Tomorrow I'll connect up one of the 'new' (to me) transmitters and TCU-30 coupler to see how the range and performance compare to my Radio Systems TR20/CP15

Maybe you all are already were aware, but I just noticed it.. So in case you didn't know... The i.AM.radio transmitter offers an outdoor version. It's basically just includes an outdoor encloser the transmitter goes in with a whip antenna attached and 100ft of cable.. the whole package is $295

Anyone using this setup?

The AM Transmitter Challenge is slated to appear in the March 2014 edition of the CQ Plus digital supplement of CQ Magazine... But you don't have to wait, you can read the compleate results now, as well as view pictures of the event at HobbyBroadcaster.net Evaluation Labs - The AM Transmitter Challenge..http://www.hobbybroadcaster.net/reviews/am-transmitter-challenge.php

A Potomac Instruments FIM-41 field intensity meter was used to test performance of five Part 15 transmitters, all with identical installations, under equal conditions, in the same location, on the same date. 1640 was used in all test since it was the only completely clear frequency available in the area.

The contenders were..

• ChezRadio Procaster
• Grain Industries GI-100/1000
• Hamilton Rangemaster AM1000
• i.A.M.Radio (both with and without use of the ATU)
• SSTran AMT5000

The 1st place winner, and the 2nd, 3rd, 4th, and 5th runner-ups are...

I'd tell yah, but then I'd have to kill yah...

Read the detailed test proceedures as well as the final results here: http://www.hobbybroadcaster.net/reviews/am-transmitter-challenge.php

The italicized text below was posted on a website used mostly by broadcast engineers by someone well known here and on many other "Part 15" boards.

Hopefully the response I posted to it will be useful to those wanting more information on this topic.

I'm going to share a little known secret or maybe a forgotten one. this is how you make poor mans radiating cable. take any 50 ohm cable put a suitable 50 ohm dummy load rated for your power level on one end and reverse the center and shield so that tx goes to shield and ground goes to center.  there you go. it will be a leaky cable just adjust your power levels for the coverage you need. I learned that from the late pastor James R Cunningham's carrier current manual.

Response -

Note to the poster of the above clip:

For a 1:1 SWR dummy load at the far end of a coaxial cable, reversing the conductors of that cable where they connect to the output terminals of a transmitter produces no more r-f radiation from that coaxial cable than if its conductors were _not_ reversed.

In such cases/configurations, equal r-f currents are conveyed in the cable along the outer diameter of the inner conductor, and the inner diameter of the outer conductor, due to skin effect. Those currents are 180 degrees out of phase with each other in both of those configurations.  

Therefore radiation from that cable after such a conductor reversal is unchanged (other conditions equal).

Known as "calls", "call signs", "call letters", "station I.Ds.", and the FCC's designation - "Call Sign Assignments", what they are is NAMES identifying individual radio stations.

In the Homeland, formerly the U.S., radio station call signs in the present day consist of four alphabet letters beginning with "W" for stations east of the Mississippi River and "K" for those toward the west.

What does the Mississippi River have to do with it? That's not what I'm here to discuss.

Prior to an earlier year K and W was assigned without regard to location, which is why legacy stations KDKA Pitsburgh, Pennsylvania, and WEW St. Louis, Missouri, are on the wrong side of the river.

No matter what side of the river Part 15 stations are on, they are not assigned call letters by the FCC. But, there is an FCC Rule governing the naming of Part 15 unlicensed radio stations.

Part 73 - RADIO BROADCAST SERVICES

(1)  Users of nonlicensed, low power devices operating under part 15 of this chapter may use whatever identification is currently desired, so long as propriety is observed and no confusion results with a station for which the FCC issues a license.

A question was raised by Rich on this website regarding our use of the calls KDX to identify our part 15 operation, based on the notion that we might be confused with a licensed station. My answer at that time was in two parts: 1.) To avoid confusion I adopted the practice of adding the number "1", saying "KDX1", when referencing my part 15 stations, but, 2.) since the FCC does not require part 15 operators to broadcast any identifying information, I don't.

Today I am considering a different answer to Rich's original question... I am considering the thought that using letters of a non-existent station, in other words, letters not currently assigned by the FCC to any station, and in fact "KDX" is not known to be assigned to any licensed station, it would be "reasonably proprietary" to use such call signs for a part 15 station.

This subject arises from my intention of attaching separate calls to each of my stations, rather than calling them all by the same (kdx) name.

Already I have established KHZ 1640 AM, the official radio station of the indoor antenna experiment.

1550 AM is now KEGO, EGO - the Station Where You Listen to Yourself.

One of my FM channels has become KLPH-FM, the station where I edit and produce The LPH (Low Power Hour).

None of these call letters show up at radio-locator.com and are presumed to be officially unassigned.

One call-set I hoped to use was KCAM, the name of my original part 15 station back in 1957, in which I appointed myself the AM translator station for local KCFM, a licensed station. But today there are two KCAMs, one AM the other FM, assigned to Glennallen, Arkansas.

But if Rich and others still oppose using letters that resemble FCC authorized stations, maybe the part 15 community should self-impose some kind of restriction against "K" and "W", and have our own letter, such as "O."

I sort of like that: "This is ODX - Oh 1550."

The part 15 rules for intentional radiation on the AM band are reasonable if this "permission" is intended to allow an individual to transmit to his own radios at home.

The combination of "100mW to the RF final" and "3-meter vertical antenna" produces just the right signal strength for use within one's home and adjacent property.

My kitchen radio is located 7-feet from my AMT5000 Wintenna installation (the metal window frame is part of the antenna), and the radio overloads from being "too close."

To reach the kitchen radio with less signal strength a second transmitter/antenna (different frequency) is located 35-feet away.

If the FCC allowed more AM signal strength all the radios in the house would over-load and it would be necessary to locate the transmitters outdoors somewhere as far away as possible, limited by the size of the yard.

It is probably true that the FCC never intended AM part 15 to reach a distant audience, although it is not expressly forbidden, for which reason much effort goes into doing just that.

Placing the transmitter in outdoor space with ground radials achieves amazing reach.

Is Radio Systems still in the part 15 business? Looks like maybe not.

I wasn't going to speak to this again, but I've had a lot of issues niggling at me, and they finally coalesced today.

First, the shootout wasn't science.  Now, before anyone goes all crazy over this statement, hear me out.

Science is a methodology in which you first form a hypothesis, then collect data in an effort to disprove it.  If you can't, then the hypothesis MAY be correct, at least until more data comes along.  You can't PROVE anything, except perhaps in mathematics.

No, the shootout was pure and simple data collection, and from a limited sample size of 1 for each of the transmitters.  That was freely admitted.

It's quite possible, and in fact, highly likely, that the results for the AMT5000 were compromised.  Because it would have been my hypothesis that the Rangemaster and the AMT5000 would be relatively similar in results, and lead the pack in terms of efficiency in delivering a signal to a Part 15 antenna (I'm not familiar with the Grain transmitter).

The fact that the AMT5000 performed relatively poorly could be from a number of factors, particularly since it's constructed from a kit, where quality control of the final product is unknown, and any number of things could happen to individual parts during the assembly process.  I've owned 4 factory assembled ProCasters, and their individual performances (in the same installation) have even varied widely.

But instead of attempting to determine the reasons why, the single sample data has been published on the Internet and a magazine.  No one is likely to read the caveats associated with it - they'll just take away the results (I'd be surprised if even 10% read the methodology used).

So while the limited data available is interesting, and a start, it's hardly the final word.  And hardly science.

Yesterday at turn-on time I noticed a frying sound on the carrier of the AMT5000. It was intermittent, sounding like short digital bursts at very irregular intervals.

Right away the back-up AMT3000 with loading-coil and advanced antenna took over the day's schedule.

Naturally the first thought was trouble in the transmitter, maybe a bad solder or aging capacitor. But with the carrier off, I noticed that static on my frequency sounded similar to the frying sound heard on the carrier.

The culprit was the strong buzz at 1700kHz, the 2nd-harmonic frequency of 5kW 850kHz, whose tower a mile away can actually be seen from the roof. That buzz was much louder than usual and was spilling over all the way to 1680kHz.

In a previous post member Rich responded to the "2nd-harmonic" that I described, telling that it most likely was not actually the station's harmonic, but was an artifact produced by radio receivers reacting to the very strong 850kHz signal.

Proof came last night when 850kHz signed off to open the frequency for KOA in Denver, and the AMT5000 carrier became perfectly clean.

Today the AMT5000 is proudly back in service.

Hi everone

Most of you know me and I have been on here for years. I have even set up
large broadcast stations,but this is not the same. The power is much less
and the effective radiated power from the antenna is really limitted by
the antenna only being 10ft tall at the most.

Here is what I need to accomplish. I live about 200 miles from the largest city.
We have a community out here mainly made up of retired people and farmers,
ranchers. I need to set up a AM radio station that can at least get 2 to 3 miles
coverage in all direction. Omini directional.

When bad weather hits here I need to get out tornado warnings,and other bad weather
reports. Some news and music. Mainly to get the weather reports out because
you would not want to be working out in a field with animals and a tornado comes.

Ok I have seen the Procaster transmitter and the Rangmaster. These are both
good transmitters,but which one has the strongest field striength coming
off the antenna. Really comes down to has the strongest radiated power
coming out of their antenna.

Since this is going to be used as a community type station I really need it
to be FCC certified. I really do not need any problems coming up when
a signal is getting out 2 or 3 miles.

Which transmitter is the best to use and has anyone found the best way to set
one of these up for maxium range.

I know alot of you have radio broadcast going out everyday to an audience
and have one of these transmitters being used.

Please help. I know a way to get out but I am going to do this the legal way.
I am a ham radio opperator as well and I do know how to build antenna,but
if I built an antenna tune to this band wow I would be way out of part 15 rules
if it was to the true length.

Anyways since the Procaster has a 10 ft antenna and the Rangemaster basically
uses a 108 inch CB antenna that breaks down to 9 ft.

Most CB antennas are about 8 feet and 6 inches.

Anyways it really breaks down to has the better antenna tuner and gets the
most signal radiated from the antenna.

Well I need to get this station up and running. I need info on how some of
you have set your antennas for max range.

Thanks
Sean

Is there someone who can explain why my reply post didn't display.The forum haven't no message to conntact me that I made mistakes about my reply. I concerned this isn't a good way to manage the forum and to treat a new member of this forum. Give me a clear answer about it.

Thank,

Louis

In these several years of discussion and learning about AM antenna systems and the limiting factor of poor ground conductivity, I have stood in respect of the scholared radio engineers we're so lucky to enjoy at this website, while accepted their pronouncement that the laws of physics are set and the best discoveries in antenna performance have been known for almost a century.

Yet a part of the brain has reserved belief that there is something else to be found; a breakthrough idea; a eureka invention. Tonight the lightbulb lit.

I call it "ground biasing," and the idea is an upside down variant of what is known as "tape bias" from the days of magnetic recording tape. What is tape bias?

Tape bias is a steady sine-wave signal fed to the record head at a frequency above the audible range, to avoid being heard as a whistle when the tape plays back. A frequency of 100kHz would be typical, and the purpose of this constant signal is to excite the magnetic particles on the tape as it rolls by causing them all to align in the same direction, dramatically reducing distortion experienced with no bias. Tuning the bias to a proper level reminds us of the class-E tuning of the AMT5000, because tape bias is set so that audio level going onto the tape peaks, but minimum distortion occurs not at peak, but a little bit past peak.

To achieve ground biasing we foresee injecting a steady sine wave tone at a frequency below the audio spectrum. Why so? For one thing, we don't want to hear this as a "hum" on the transmitter's modulated signal, but the lucky second reason is that earth resonance resides down low, around 8Hz, a fact exploited by the Navy with ELF (Extra Low Frequency) buried antennas for sending radio signals to submarines submerged in the ocean. The ELF signal excites the magnetic corridors of the earth and travels thousands of miles in earth and water.

By "exciting" a set of AM ground radials at around 8Hz, we anticipate a marked improvement in antenna/ground conductivity. This should increase antenna efficiency by "N," to employ John WXCD's unknown number figure.

Even if it doesn't work, think of it, we can sell thousands of 8Hz Bias Generators and move to New Zealand where 1 Watt FM awaits.

All joking aside, my invention of ground bias will be my creed whether it works or not.

It was (guessing) 2005 when I ordered and built the first AMT3000, using a glue stick to paste the enclosed white wire up the wall which gave a good indoor signal. It would be several years before I woke up about the advantage of good grounding.

In March 2007 I broke through the digital wall and began experimental test streaming by Shoutcast, the last stunbling block having been "port forwarding."

KDX Worldround Radio was formally dedicated on June 1, 2007 and has been making noise ever since.

My station serves me with hand-selected programming that I'd enjoy hearing if anyone else broadcast it, but they're not, so I am. Two transmitters are in use now, but only one at a time.

While indoors it's the AMT3000 which blankets the house with a solid signal, and when outdoors or driving in the area it's the AMT5000 which screams out farther than I would be comfortable with at all times. It gets shut-down unless I'm outside.

Carrier current and shortwave are side-tracked awaiting touch-up engineering, and long wave is still a schematic on paper.

As far as "the community" is concerned, I don't know them and would feel silly providing unsolicited programs on the assumption they'd have any interest. As far as I can tell they gather for superbowl, baseball and other sports viewing on their home theaters, make cell-phone calls while driving SUVs, or export dog feces and urine up and down the street during dog walks.

The licensed stations continue spewing their bottomless sports talk and recycled gospel stories but I do scan them as a way of re-discovering how wonderful my personal radio station is.

The Part 15 and low power stations of the world have become the talent sanctuaries in preservation of radio art, elderly disk jockies and inventive engineering.

Join the ALPB.

We have been wrong to think that part 15 radio stations are unlicensed. It's all in word definitions.

License as a verb means "give permission." Part 15 of the FCC Rules gives permission to OPERATE... another key word:

Operate is a verb meaning "to function." Look at the word's appearance in 15.219:

15.219 OPERATION in the band 510-1705 kHz.

That single line grants PERMISSION to FUNCTION in the AM medium wave band, in other words it grants LICENSE to function.

For those who think a license is a piece of paper we point to the word LICENSE as a noun... which refers to the permission we have as well as a document recording that permission.

The Part 15 Rules themselves are a document recording our permission to operate, and so stand as a valid license IN THEMSELVES.

At the same time there is no prohibition against expressing key portions of the part 15 permission on a self-styled document suitable for framing and hanging with signature and seal.

Government publications and symbols are in the public domain and as long as truly reflecting the contents of part 15 can be employed to form a legal and proper document.

This point of view is beyond refutation.

http://www.classeradio.com/tuning.htm

Has anyone mounted a talking house outdoors?

How would you go about doing that - considering the "special" wall-wart and the weird size of the thing...

I think I saw somewhere some sticking one in a 5 gallon plastic "paint bucket"..

The following pictures show the voltage waveforms at the MOSFET drain terminal (test point T4 on the circuit board) for various settings of the tuning trimmer capacitor. Freq = 1550kHz, Antenna Capacitance=30pF, Rrad+Rgndloss=33ohms. "PWR IN ADJUST" control unchanged. It was set for 100mW for the 3rd picture below, but was left unchanged from that setting for all the others.

I am hoping that this will help convince everyone that an oscilloscope is NOT required for tuning. Instead, simply adjust the coil tap jumper and trimmer for maximum input current, then adjust the trimmer 1 full turn clockwise, and then adjust the "PWR IN ADJUST" control for 100mW input power. This simple trimmer "trick" works very well over the 1350kHz - 1700kHz frequency range of the toroid coil and an antenna ground loss resistance range of 10ohms - 75ohms.  

Notice particularly that the "Power In" is maximum when tuned for max power in (first picture), but the efficiency is only 78%. When tuned to maximum efficiency, the Power In drops, but that drop is compensated for by the final tuning step where you set the power in back to 100mW. The radiated signal power is maximum at the highest efficiency tuning point and 100mW input power. All other tunings with legal Power In will result in lower radiated signal power.

If you want to use an oscilloscope, connect the probe to test point T4 (MOSFET drain) and connect the scope probe ground to test point T1 (ground). Maintain the scope trigger for a stable display. Adjust the coil tap jumper and trimmer to get maximum input power on your voltmeter. The scope should show the first waveform below. Then adjust the trimmer to approximate the third picture below. Then adjust the "PWR INPUT ADJ" control for 100mW.

Tuning trimmer set for maximum input current meter display

Power In = 0.140W

MOSFET drain efficiency = 78%

Tuning trimmer set .42 turn clockwise (+.3pF)

Power In = 0.131W

MOSFET drain efficiency = 93%

Tuning trimmer set 1 turn clockwise (+.7pF)

Power In = 0.100W

MOSFET drain efficiency = 99%

Tuning trimmer set 1.4 turns clockwise (+1.0pF)

Power In = 0.058W

MOSFET drain efficiency = 99%

Tuning trimmer set 2  turns clockwise (+1.4pF)

Power In = 0.037W

MOSFET drain efficiency = 94%

Tuning trimmer set 3 turns clockwise (+2.1pF)

Power In = 0.028W

MOSFET drain efficiency = 60%