Source: http://aa7ee.wordpress.com/2010/10/08/the-sstran-amt3000-a-part-15-am-transmitter/
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The SSTRAN AMT3000 – A Part 15 AM Transmitter | Dave Richards AA7EE
The SSTRAN AMT3000 – A Part 15 AM Transmitter	Filed under: Part 15 Broadcasting — AA7EE @ 6:12 pm Tags: AMT-3000, AMT3000, Low Power Unlicensed Broadcasting, Part 15 AM, Part 15 broadcasting, SSTRAN, SSTRAN AMT-3000, SSTRAN AMT3000
Your own mini AM broadcasting station (substitute the phrase "medium wave" for AM if you're in the UK.)
\This loading coil is BEEFY.
Schedule 40 pipe and Rubber-maid containers - the giveaway signs that this is not a high-tech installation on the roof of some government building, but just another radio experiment at my house.
If this Part 15 thing doesn't work out, perhaps I could use it on Top Band......
Dave – good to see you back! You don’t post often, but when you do, it’s a doozie!
I’m curious about your antenna. How tall is the vertical part and what are you using as an RF ground? And do you plan to keep operating the transmitter from right at the base of the antenna? As I’m sure you’re aware, even the cheapest brand of RG50 you can find would have minimal losses at the freq your operating. Locating the transmitter away from the antenna might solve your hum problem…
Comment by John AE5X — October 8, 2010 @ 8:48 pm | Reply	John – I read your posts often. As I don’t read many radio magazines these days, your blog keeps me up to date with interesting new ham radio kits and ideas. Many thanks!
The FCC ruling which applies to my transmitter is Part 15.219 – “15.219 Operation in the band 510-1705 kHz.
(a) The total input power to the final radio frequency stage (exclusive of
filament or heater power) shall not exceed 100 milliwatts.
(c) All emissions below 510 kHz or above 1705 kHz shall be attenuated at
least 20 dB below the level of the unmodulated carrier. Determination of
compliance with the 20 dB attenuation specification may be based on measure-
ments at the intentional radiator’s antenna output terminal unless the in-
tentional radiator uses a permanently attached antenna, in which case com-
pliance shall be demonstrated by measuring the radiated emissions.”
As you can see from (b), using coax to feed the antenna would put me in violation of the rules.
The problem a lot of Part 15 operators have is when they wish to mount the transmitter and antenna high above ground level.
Although the Part 15 rules aren’t completely clear on this, from the results of FCC inspections of Part 15 stations that have taken place, some Field Inspectors are satisfied with elevated installations if it can be demonstrated that the long ground lead is not radiating. This is done by taking field strength measurements with the ground lead connected and then disconnected. Some Part 15 operators install RF chokes or other types of filters to prevent their ground leads from radiating.
Of course, the easy way to ensure compliance is to mount the transmitter and antenna at ground level so that the ground lead is very short. That way you can get a good RF ground with an installation that will almost definitely pass inspection.
I’m using a piece of solid wire that connects to a nearby cold water pipe for a ground John. I don’t know if it’s a good RF ground or not, but it’s kind of a moot point because I am supposed to insulate the ground lead from radiation, as my installation is about 15 feet above ground. My ground lead does pass through a ferrite core at the transmitter end (you can see it in the close-up picture of the transmitter box) but I don’t know how effective it is. Obviously this arrangement will have to change in some way if I am to continue with this external antenna.
This has made me realize how much easier the constraints are to us QRP operators. 5 watts into any antenna system seems like paradise compared to these Part 15 restrictions. Nevertheless, I’m glad that we are allowed to emit any kind of RF at all on this band.
Comment by aa7ee — October 8, 2010 @ 10:36 pm | Reply	In answer to your question about the vertical tube John, it telescopes for exact tuning, but the approximate length for my vertical part when tuned is 101″. That leaves approximately 19″ more for the lead to the loading coil, the length of the loading coil and the ground lead. It’s not much!
Comment by aa7ee — October 8, 2010 @ 10:43 pm | Reply	Thanks Dave – I knew that was a restriction on the 160-190 kHz Lowfer band but didn’t realize it applied here as well. With ~60 mW (based on 100 mW ‘input’) from the transmitter coupled with the imposed inefficiency of the antenna requirements, your ERP is probably in the single digit microwatts.
Comment by John AE5X — October 8, 2010 @ 11:58 pm | Reply	Dave –
Below is a clip from a post I made on the web on the subject of long, radiating conductors between an elevated Pt 15 AM tx + 3-m whip and a functional r-f ground. Maybe you will find it interesting.
Re: Setting new precedent for outdoor Part 15, From Keith Hamilton
« Reply #18 on: July 10, 2010, 10:21:58 AM »
Quote from: (omitted) on July 10, 2010, 09:02:42 AM
\\ It is my opinion, that no matter what ‘corrective’ action was taken at KENC, it would never be good enough. Seems to me that this particular agent and his office have it out for Ken Cartright.//
The FCC would have no legal basis per 47 CFR Section 15.219 to cite any unlicensed, intentionally radiating transmit system in the AM broadcast band that actually met 47 CFR Part 15.219.
However it appears from the FCC NOUO that KENC did not do so before the filter was installed, and that installing the filter “made no appreciable difference” to that determination.
This whole issues revolves around the total length of the conducting path between the transmitter and the functional r-f ground used by the Part 15 AM system (something buried in the earth, typically).
Some Part 15 AM microbroadcasting proponents define the “ground lead” as stated in 15.219(b) to be limited to a short conductor attached from the transmitter to the top of second conductor, and that a Part 15 AM system meets Part 15.219(b) as long as the sum of the length of that short conductor and the length of whatever conductor is attached to the antenna connector of the transmitter does not exceed 3 meters.
That second conductor is defined by these proponents to be “ground.” In the KENC case, the length of that second conductor (the tower) appears to have a length of something like 40 feet, where it connects at its base to one or more buried ground rods — which ground rods are the functional r-f ground for the system.
What if a single 40-foot conductor was used between the transmitter at the top of the tower and the ground rods? Probably those same proponents of Part 15 AM microcasting then would recognize that such a configuration would not be compliant with 15.219(b).
But physics and field experience show that there is no practical electrical difference in the performance of a Part 15 AM system using a single 40-foot “ground” conductor, or one using two conductors in series whose total length is 40 feet — where the shorter length is called a “ground lead” and the longer length is called “ground.” Calling the longer lead ground doesn’t make it function as a ground, as far as r-f energy is concerned.
The accurate definition of a ground lead used at radio frequencies is the conducting path leading from the r-f ground terminal/chassis of an electrical device, and connecting it to a functional r-f ground (ground rods, or similar).
Such long conducting paths (whether comprised of one conductor or more) between the transmitter and a functional r-f ground carry all of the r-f current that the transmitter can produce in that installation.
An r-f current flowing along a conducting path between the ground rods and the transmitter produces radiation. That is the reason that 15.219(b) includes the length of that conducting path in the 3-meter limit. Effectively it is a radiating part of the antenna system, along with the “3-meter whip.”
Comment by R. Fry — October 10, 2010 @ 7:42 pm | Reply	Your comments make perfect sense Rich and it was a very similar line of reasoning that made me realize that if I am to operate a Part 15 station with an elevated installation, the only antenna configuration whose compliance I would feel confident in would be one in which there actually is no ground lead and the 2 antenna wires connected to the transmitter comprise a much-shortened dipole antenna.
The transmitter I am using has chokes on the circuit board that prevent RF currents from flowing in the power leads and the ground side of the audio input cable, so such a set-up should be compliant with 15.219
Comment by aa7ee — October 11, 2010 @ 1:44 pm | Reply	While Mr. Fry brings up some *interesting* observations he is not the FCC. The 15.219b rule simply states “and ground *lead* (if used)” which anybody proficient in the English language will interpret as the wire between the device and the ground. The FCC rule is vague but Mr. Fry believes he is the sole authority for on both the rules and the FCC interpretation. Mr. Fry believes his personal interpretation of what ground *lead* is the Gospel truth and anybody who disagrees with his point of view is not only wrong but is of lesser intelligence. There are many and multiple instances of this never ending rant spewed across many radio and hobby oriented online forums.
The only thing Mr. Fry fails to acknowledge time and again is that various installations have been inspected by FCC inspecters and given a passing grade. His must believe his one year of broadcast engineer allows him to play the expert.
Comment by Rob Martin — October 11, 2010 @ 3:07 pm | Reply	Rob Martin wrote, “While Mr. Fry brings up some *interesting* observations he is not the FCC. The 15.219b rule simply states “and ground *lead* (if used)” which anybody proficient in the English language will interpret as the wire between the device and the ground.”
And I do, however no interpretation is necessary. A functioning r-f ground does not exist at the top of vertical “massive wire” or any other conducting path such as a tower, flagpole etc. Physics, and the experience of the “Part 15 AM” operators who were cited for using long, conducting paths to a functional r-f ground (something buried in the earth) both show this to be true.
“The FCC rule is vague…”
No, I submit that an accurate understanding of the rule is what may be vague.
“His (sic) must believe his one year of broadcast engineer allows him to play the expert.”
My broadcast engineering experience includes the list below, which starts in 1959 and was continuous for over forty years through my retirement from Harris.
* RF Applications Engineer, Harris Corporation Broadcast Division
* Field Supervisor, AM/FM/TV Broadcast Service at Radio Corporation of America (later: RCA Corp)
* Staff Engineer at WJR, The Goodwill Station (Detroit)
* Chief Engineer at WSAM and WSAM-FM, Saginaw, MI
* Staff Engineer at WKNX-TV, Saginaw, MI
* Chief Engineer at KPLY (AM), Crescent City, CA
Comment by R. Fry — October 11, 2010 @ 8:12 pm | Reply	Hello Dave, Nice to see another post on your station again. I continue to keep reading and learning about micro broadcasting. As luck would have it, I ran across a micro broadcaster at a local “car show” this weekend. They were using it to keep event participants informed about the activities at the show and playing 60’s music. They also had it “hard wired” with speakers placed along the course which covered about a mile. It worked well but were only getting about 1/4 mile range (over the air) due to the tall buildings and the transmission site along the river. They were using a steel whip for an antenna. The audio was excellent for an AM station. I’m not sure I could solder as well as you…so have been looking at the Ramsey FM 25B which is a little more “basic”. With a little luck, I might be able to put this kit together and will probably use a “dipole” antenna. (perhaps a set of rabbit ears extended the proper length) for the first test. I’m faced with antenna restrictions here at home and would not be able to place a steel whip in the attic. You’re right about the difference between Ham radio and broadcasting…antennas are NOT a problem with ham radio. Sorry to hear about the “hum”. Hope you will be able to work out this “bug”. I can’t help but be concerned about the transmitter being so close to the antenna on your set up. Not much of an electronics background here so may be worried about something that makes no difference? I assume you hope to minimize power loss to the antenna. Thanks again for posting. I’m making broadcasting friends here in the valley but the going is slow. My time line is still around the first of the new year. I’ll be looking forward to reading more about your station there. 72’s
Comment by John N8ZYA — October 14, 2010 @ 1:03 am | Reply	Hi John – Glad you got to see a Part 15 AM station in action. I wish I had seen that one.
Have fun with the FM transmitter. If you’re thinking of eventually covering a greater area than your house, it is much harder to do on FM while still remaining within the constraints of the FCC Part 15 rules. The restrictions for Part 15 FM broadcast band devices pretty much ensure that you won’t cover greater than a 200 foot radius from the transmitter. Have fun with it though – it sounds like a worthwhile project.
Good to hear that you continue to enjoy listening to “Auntie Beeb” as she is affectionately known in the UK.
Comment by aa7ee — October 15, 2010 @ 12:06 am | Reply	Nice Blog Dave. You are indeed a minimalist with ur QRP AM and amateur station. See you on Hobby Broadcaster
Comment by John — October 14, 2010 @ 2:21 pm | Reply	Hello Dave, Actually they have a beginner AM kit which costs at about $35. I think I’ll try that one just as a test unit. It’s manually tuned (with a pot) but only 100 solder points and estimated completion to assemble is 3 hours. Even I should be able to put that together. hihi. I’ve been looking at some audio mixers and mikes. I’ll keep it simple at first to see how it goes. It should be fun. Still thinking of AM for the distance.
Comment by John N8ZYA — October 18, 2010 @ 2:16 am | Reply	Hi Dave,
I have a transmitter setup similar to yours except I also added 30 20-foot ground radials.
Beside the radials, I also have 4 ground rods about 6 feet apart driven at a 45 degree angle.
Not much choice since my yard is 5 feet of soil over bedrock.
Are you sure the ‘hum’ is on the carrier, not the audio ? I had hum on the audio that went away when I unplugged the audio feed.
My transmitter is about 200 feet from the house and I had to isolate the audio ground with a RadioShack ground look isolator. Tuning also took a while using a mix of a Digital meter, a scope and an old AM receiver with a real signal strength meter. I get about 1.5 miles all around except to the east, there I get almost 4 miles.
It must be some kind of underground iron ore vein or something :)
Comment by Andre — October 19, 2010 @ 7:35 pm | Reply	Andre – your experience, along with the comments I’ve received from others, makes me realize how very important a good RF ground is for these small Part 15 AM transmitters. Most of my experience is at higher frequencies where groundwave propagation doesn’t happen as much.
Comment by aa7ee — October 21, 2010 @ 3:45 am | Reply	RSS feed for comments on this post.	TrackBack URI
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