FWIW, as an amateur, I can say for absolute sure that proper grounding is critical to AM operation. If you look back through the messages on this thread, you'll see that in common with most of them. This is because AM signals, especially at low to midband frequencies, go near the surface during daylight hours. This is why big AM stations are usually found in the middle of a fair-sized field. Recommended radials, i.e., wires or ribbons of copper are 120 (one every 3 degrees) at about 100' each laid radiating out from under the tower. These are grounded via deep-driven stakes at the base, and often shorter ones at the ends, and sometimes the ends are connected to each other all the way round.
For a hobby setup, you can get away with fewer, maybe 30 (12 degrees) at 20' each. But, generally, more is better ... up to a point. After that you're wasting time and money.
But I don't do that for my single setup because I have the best advantage you can have: My TX and antenna system are on my boat moored in a seawater marina. No natural ground is more conductive than the sea. With a little height, 3' tripod, 8' fiberglass mast, 10' of antenna and coil, at about 7'-8' above the waterline (cabin roof), I get good signal in town and out to my studio, and it's been heard as far away as 3 mi. out the valley, in a direct line from the marina (fatiguing to listen to at that range of course).
But, even in town, the signal often gets beat up by atmospheric conditions, traffic, florescent lamps in buildings, power lines and booster transformers, underground utilities, skywave interference from far away high-power stations on the same frequency, etc., etc. I don't have and cannot afford an Inovonics 222.
Yesterday it was cloudy most of the day, but I was bangin' out good listenable signal in most places around town with corridors to the port. Today, it was nice out right here, but a little breezy (nothing bad, though) and it's been lousy all day. Some static, even right down at the port shore ... couple hundred yards away from my boat line-of-sight. But I could see T-storm build-ups 80-100 miles away. I'm sure that's what's been affecting it today.
At these flea-power levels ...that's AM radio.
I have a real simple set up. My Rangemaster is mounted on a pole about 25 feet up. Transmitter is grounded to the pole with about 6" of insulated (not that it makes a difference) ground wire for lightening protection. The bottom of the mast is clamped to a 8 ft ground rod that I hammered straight into the dirt just inches from the bottom of the mast. A proper tune and thats it. There are big trees all around the antenna too.
When I say great range I mean its listenable for a several miles on a car radio**, however, it will stop the scan on my car radio no more than 900 feet from the Rangemaster with FULL modulation. Keep in mind we are talking toy walkie-talkie power here, so a grade A signal like the big boys cannot be expected outside a block or so.
** AM Radio reception in cars varies. I had a '91 Honda that generated so much motor noise on AM, I couldn't hear it unless I turned the engine off. The wife's car I could hear it for miles while driving.
Chuck said, in one of his posts in this thread, that if he does not get more range from his AM transmitter, he is thinking about operating as an FM pirate. He is confident about not getting caught, because he believes that the FCC does not go after "little operators." I decided to test this supposition by calculating the EIRP (ERP with respect to isotropic) based on the field strength readings for the latest 40 FM NOUOs on the FCC website. The 40 NOUOs were for only 32 stations, because some stations were issued more than one NOUO. Sometimes, if the illegal operator is not known, the owner of the property is issued an NOUO first. Then, the property owner quickly contacts the FCC to identify the operator, and the operator is also issued an NOUO.
The legal limit of 250 uV/m at 3 meters corresponds to an EIRP of only 18.75 nanowatts. This Forum has seen a smaller ERP mentioned, but this was based on an ERP with respect to a half-wave dipole in free space. For the 40 latest NOUOs, the largest EIRP was 7110 watts, and the smallest was 19.7 uW. Of the 32 stations cited in the 40 NOUOs, Here is how I classified them by EIRP:
0 - 1 mW: 2 stations
1 - 10 mW: 0 stations
10 - 100 mW: 8 stations
100 mW - 1 W: 15 stations
1 W - 10 W: 3 stations
10 W - 100 W: 3 stations
100 W - 1 kW: 0 stations
1 kW - 10 kW: 1 station
Of the 32 stations, 25 were less than 1 W, and only seven were more than 1 W. 10 stations were less than 100 mW, and two were less than 1 mW. I think that this shows that the FCC definitely does go after "little operators."
Maybe the definition of "little operator" needs some clarification.
If my math is correct, the lowest power shown above, 19.7 uw is 1050 times the 18.75 nw (legal level), or over 30 dB stronger...at 50 ft. this would be around 1.62 mv/m, quite a jump from 50 uv/m. This would give a signal (theoretically) of 81 uv/m at 1000 ft. I would assume a usable signal might exist at a mile or two.
I wonder if you were over the limit by a small amount, say 60 uv/m at 50 ft., if they would still issue a NOUO. But 32 times the limit (as above) would definitely be pushing it, it seems...
In certification testing of Part 15 FM transmitters, the industry standard for the compliance testing site is +/- 4 dB accuracy of the field strength measurement. Since even a calibrated test site at a compliance laboratory has a possible error of +/- 4 dB, there certainly is no justification for issuing an NOUO based on an FCC field measurement only somewhat higher than the limit in Section 15.239. The field strength measurements in NOUOs are so high that there is no doubt that the legal limit is exceeded.
I have read statements on Part 15 discussion boards that the FCC will accept FM transmitter output powers of up to 100 mW. This is not the case, as my survey of NOUOs shows.
There is also an opinion seen on the discussion boards that field strength measurements are a lot more accurate than they really are.
Be critical of what you read on discussion boards.
There is a problem on discussion boards (and in scientific discourse in general) that someone becomes distinguished in some way, and has become an authority figure. The other members of the board tend to accept his authority uncritically because there is a long history of his opinions being correct. Unfortunately, he is also believed even when he is wrong.
It depends on where you live. There are several 1 watt or less FM stations in operation in the Tampa Bay area with full knowlege of the FCC. Many have been running for years. The stations include drive-in theaters, race tracks, college campuses in St Petersburg and God, Guns and Guts stations, all in the FM band and clearly above the 250uV level with regard to range.
They do crack down on higher power pirates in the Tampa Bay area and Orlando.
87.9 MHz (LPR) Joyland Drive-In, Dade City; active during movie times
89.1 MHz (LPR) Auburndale Speedway; auto racing.
89.3 MHz (LPR) Fun-Lan Drive-In & Swap Shop, Tampa;
89.5 MHz (LPR) USA International Speedway, Lakeland
95.9 MHz (LPR) "Old-Town Radio", Kissimmee
96.7 MHz (LPR) “96.7”, Clearwater WKID
96.7 MHz (LPR) "Absolute Radio", Seminole;
96.7 MHz (LPR) Pinellas County Sheriff’s Office
99.9 MHz (LPR) "WECX - 99.9 Eckerd College Radio
102.9 MHz (LPR) "Lutz Community Radio"
to name a few..
Though we drift from the topic of the OP it is probably OK since adequate answers have already been provided.
With this in mind, I wish to reply to Ermi's comment:
There is a problem on discussion boards (and in scientific discourse in general) that someone becomes distinguished in some way, and has become an authority figure. The other members of the board tend to accept his authority uncritically because there is a long history of his opinions being correct. Unfortunately, he is also believed even when he is wrong.
This is true and the history of science confirms this. This is why responsible publications subject submitted scientific papers to critical peer review before publication. I know how this works having been both a reviewer and having been reviewed. The situation on discussion boards is that the posts are not reviewed before publication and the opportunity for peer review exists on the boards after publication. As long as the reader recognizes this and the critiques are kept impersonal then I see this as legitimate since it is the nature of discussion boards.
If there is a situation where a post is contradictory to an "expert's" posting then the reader needs to consider both sides of the discussion. A poster's acknowledgment of an error made by himself goes a long way in establishing the truth as well as the poster's credibility and the same can be said regarding the reviewer. Unfortunately, often this becomes a battle of the wills rather than a pursuit of the truth. Readers need to keep this in mind.
Another misconception is that there is consensus in science. There is not. Voting does not establish scientific fact. It is possible that a majority of scientists agree with a certain hypothesis but this does not make it true. Minority dissenting opinions need be evaluated based on fact and not on the basis that few hold that view. This also applies to the reputation of those participating in the debate influencing the acceptance of the hypothesis. So if five people on a board agree and one disagrees this does not make the one wrong (nor right).
Neil
The illegal transmitter at the Sheriff's Office is a bit of a surprise, especially since Florida law calls for the enforcement of Federal law relating to pirate radio. However, unless you are as confident of the state of enforcement in your area as wdcx is, it's probably better not to use illegal FM transmitters. FM is much more strictly enforced than AM.
BTW, because of the standard +/- 4 dB error of the test sites at compliance laboratories, a certified transmitter will be tested for a lower field strength (at the lab) than 250 uV/m at 3 m.
I found five FM NOUOs issued by the FCC Tampa Office since 2003, but these were for only three stations. Maybe there were more NOUOs, but five were all I was able to find on the FCC website.
All three stations were visited more than once, with the field strength measured during each visit. This gave the opportunity to see how consistent the FCC field strength measurements are.
For the NOUOs issued to Dorlis and Eliphone on November 29, 2006, the EIRP calculations corresponding to the field strength readings are 332 mW and 1.25 W. The readings are consistent to 5.8 dB.
The NOUOs issued to Charles and Pierre-Francois on July 26, 2006 resulted in EIRP calculations of 12.2 W, 16.4 W, and 17.6 W. The readings are consistent to 1.6 dB.
The NOUO issued to Lawson on August 3, 2005 resulted in EIRP calculations of 26 W and 45.7 W. The readings are consistent to 2.4 dB.
We see from this that the Tampa Office does not issue a lot of FM NOUOs, and, and two of the three stations that were cited had EIRP levels in the double-digit watts. One station, however, had comparitively low power. wdcx supplied an impressive list of FM violators known to the FCC (including a Sheriff's Office) who are under the juristiction of the Tampa Office, but we see that the Tampa Office does, occasionally, enforce the rules relating to FM, and sometimes it will issue an NOUO to a relatively low-power station.
The variability of the field strength readings for the same station on different days suggests to me that field strength measurement is not as exact as some on Part 15 discussion boards have suggested.
During my search for NOUOs issued by the Tampa Office, I accidentally found an NOUO issued to the City of Sublimity, Oregon because of a KENC transmitter located on a water tower there. I discussed the Sublimity NOUO on another thread.