Rich
Full Member
RF Systems Engr (retired)
Posts: 112
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Post by Rich on Feb 18, 2019 13:29:33 GMT
This post is lengthy, technical, and probably will need some study to understand — but for those who may be interested...We have a grant pending for a TR6000 Model 15.73 Transmitter to operation as an educational institution under FCC Part 15.221. etc Under 15.221 you are afforded extra liberties within part 15 limits, one being your not restricted by antenna length or power. ... I mean couldn't you simply extend the wire to your hearts content to increase range providing it stays within the boundaries of whatever your institution covers? - Or is that area small making 15.219 a better option? RE: 47 CFR §15.221 - Operation in the band 525-1705 kHz. (Text attributes added)
(a) Carrier current systems and transmitters employing a leaky coaxial cable as the radiating antenna may operate in the band 525-1705 kHz provided the field strength levels of the radiated emissions do not exceed 15 uV/m, as measured at a distance of 47,715/(frequency in kHz) meters (equivalent to Lambda/2Pi) from the electric power line or the coaxial cable, respectively. The field strength levels of emissions outside this band shall not exceed the general radiated emission limits in § 15.209.
(b) As an alternative to the provisions in paragraph (a) of this section, intentional radiators used for the operation of an AM broadcast station on a college or university campus or on the campus of any other education institution may comply with the following:
(1) On the campus, the field strength of emissions appearing outside of this frequency band shall not exceed the general radiated emission limits shown in § 15.209 as measured from the radiating source. There is no limit on the field strength of emissions appearing within this frequency band, except that the provisions of § 15.5 continue to comply.
(2) At the perimeter of the campus, the field strength of any emissions, including those within the frequency band 525-1705 kHz, shall not exceed the general radiated emission in § 15.209.
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The graphic below shows what might be expected for the coverage radius of a legal Part 15 AM system operating under §15.219, for the various conditions shown in the graphic.
Observations:
- Sub-paragraph 15.221(b) is specific about applying only to the campus of educational institutions
- The radiated emission limit at a distance of 30 meters from the transmit antenna on a frequency of 1650 kHz for a system meeting §15.209(a) is 24000/1650 = 14.54 µV/m (approx)
- The first row of the table in the graphic below shows that even the worst-performing system considered there produces about 3.8 times higher field intensity at 1 km than permitted under §15.209(a) at 30 meters
Conclusion:
Unless the perimeter of the FCC-defined campus includes a geographic area of quite a few square miles, a legal, unlicensed system operating there under §15.219 could provide much greater signal strengths at the perimeter of that campus than one operating under §15.221.
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Post by sparepart on May 20, 2019 1:36:42 GMT
Bill Baker:
We promised to notify you when the Range Extender for the Talking House / I A.M. Radio Transmitter was ready for you to purchase. Our estimation was that the first group of them would be ready in the springtime; and, the good news is that we are going to hit that target! Assembly of the first flight of Range Extenders (v 2.5) began this month, so the next message you get will tell you that yours is ready to ship! Your package will include the antenna tuner in an outdoor enclosure, antenna with mast/wall mount, 25’ coaxial cable (RG6) and instructions. Freight is included to the lower 48 states.
The suggested retail price is going to be $395, but because you submitted a $50 deposit, you will be purchasing the unit for $295, which is $100 off! We will contact you directly to complete the transaction within the next few weeks.
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w9lwa
New Member
Posts: 43
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Post by w9lwa on May 21, 2019 0:30:18 GMT
Well, I suppose I'm a bit confused. So what we have here is 25 feet of coax between the antenna tuner and the rest of the transmitter? This much coax doesn't sound legal to me, so what did they do to make it legal? Has the FCC determined that the antenna lead does not include footage on the transmitter side of the AT? If so, would this not allow most of the transmitter to be at ground level and the AT and the antenna to be 25 feet up the mast? Wouldn't that take care of both the antenna lead and ground lead issues?
Back in the days before the ground lead was included in the antenna and antenna lead length (Pre-1975, I think that was) it was just a matter of moving the transmitter up the tower to eliminate a long antenna lead. If the above and foregoing supposition is what is going on with this range extender, we're now just dividing the system someplace within the transmitter. I suppose the question is now where the best place is to separate the transmitter components with a long lead. Is it indeed between the AT and the rest of the transmitter?
I think we're looking at a worthwhile development here.
All comments appreciated.
John W9LWA
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Post by End80 on May 21, 2019 3:06:40 GMT
Well, I suppose I'm a bit confused. So what we have here is 25 feet of coax between the antenna tuner and the rest of the transmitter? This much coax doesn't sound legal to me, so what did they do to make it legal? ... The extended cabling for the unit is nothing different as with the original ATU that was FCC certified with the Talking House over a decade ago --
Anyway, this issue of the ground lead arose back in the 70s to put a nip in the bud to keep the federal and state highway departments from expanding their use of Part 15 as an unlicensed means of establishing a national travelers radio service. Then the FCC began issuing experimental licenses with more power and longer antennas around 1974 and eventually establish licensed TIS in 1977..
Despite the way the rules are written, Part 15 is and always has been governed more by maintaining it's range, than by the specifics of antenna/lead length. The design of the Talking House itself as well as it's optional ATU (both the old and new) are but one evidence of this, but it becomes even more obvious through the observance of it's historic use.
Anyway... all I was really going to say was that the 25 foot of cabling between the TH and the ATU is nothing new, what's new (presumably) is that the new unit has been improved over the original one.
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w9lwa
New Member
Posts: 43
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Post by w9lwa on May 21, 2019 4:46:40 GMT
So you are saying it's technically illegal but the FCC lets people get away with it?
I don't know how any responsible person could risk that now, let alone if the penalties are increased if the anti-pirate bill becomes law...
Scares me and I was fearless up until now.
On the other hand, doesn't the manufacturer of this thing say it's certified legal with the coax? If not somehow legal, they couldn't possibly certify the product with 25 feet of coax. There must be more to the story and I don't think it's just because they think the FCC will let them get away with it - although I suppose stranger things have happened.
Appreciate your comments.
John W9LWA
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Post by End80 on May 21, 2019 15:26:28 GMT
What I'm saying is controversial, but it's undeniable. There's two issues at play with Part15AM:
1. The letter of the rule; which stipulates the entire antenna/ground lead length must not exceed 3 meters 2. the documented, established and accepted wide spread practice of the last 50 years; being pole or building mounted transmitters with at least 6-10ft of ground lead (or more).
There's also the Talking House which received it's FCC certification in or around 1982 and has been mass produced by many thousands of units since (the most popular unit ever used), yet by it's very design it's ground lead has always far exceeds the three meter length limit - and then if you include the ATU the antenna system is extended even further..
So yes, in a manner of speaking, the Talking House as well as it's ATU always been technically illegal in regard to the way 15.219 is worded, but the FCC has always allowed it.. However, in all cases of part15AM use of any 15.219 transmitter, in the 1960s, 70s, 80s, 90s, on through the 2000s, the range never exceeded the capabilities of what a compliant 15.219 system -which is approximately a maximum of a half mile from the transmitter (or a mile radius).. any which exceeded a mile risked citation by the FCC inspectors then applying the three meter rule.
A Part 15 AM transmitter is incapable of ever transmitting farther than about a mile radius with 3 meters antenna system and 100mw of power, and based upon it's historic implementation, that has always been the primary stipulation of it's continued use - and never the actual length of it's components.
Yes, it's convoluted, but that the way it's always been. The greatest damage to hobbyist partaking in part15 broadcasting (ironically) has not been from FCC pressure, but originated right here in the hobby forums about 10 years ago when the idea of installing our outdoor transmitters inches above the ground became an objective. Such practice has never existed before, nor is it reasonable.
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Post by End80 on May 21, 2019 15:34:11 GMT
Oh, and just to clarify.. The Talking House system was designed and FCC certified for 40 years now with a ground lead that exceeds the rule limit - and that makes it 100% legal. Weird huh? But true.
Unfortunately the Talking House is also one of lesser capable when it comes to range, but using the ATU does apparently help a bit.
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Post by Admin on May 21, 2019 19:51:15 GMT
It's a matter of interpretation. The ATU is actually the final stage of the transmitter. So the coax is just inter-stage coupling between an exciter and final stage. The antenna is connected directly to the final stage with about 3 inches of wire. Of course the immediate response to this would be that the final stage is the last active component, not the tuner.
Putting the Talking House at the top of a pole and running power and audio cable to it would yield the same result as using the ATU. In fact, during all the controversy over the ATU, the ISS Infospot system did just that when the ATU was temporarily abandoned. And now, they have returned it to production, for sale, with the original certification provided by the FCC.
Regardless, the engineers at the FCC aren't stupid. They received the independent lab certification report and issued a certification for the system to include the Range Extender ATU. Can't dispute that.
Opinion has been expressed concerning both sides of the discussion. No reason to beat a dead horse.
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