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1-2mW into 50ft of rg58 type cable into a single element 19″ whip at 88.9mhz. BNC on one end pl259 on antenna end. antenna end will have RG wrapped a few turns around toroid to minimize cable radiation.
can any of the experts run the numbers and estimate if i would be within part 15 fm limits?
i’m guessing with cable losses and whip mismatch that it should come within spec.
Total posts : 45366Well with 1 or 2mW running in 50 feet of RG 58, it will most likely be within a reasonable range of 239. I don’t bother with the numbers at 1 or 2mW. If it was a watt or two and going through the same coax with an attenuator or two then ya I would run some numbers, but numbers on paper don’t mean that’s what happens in the real world.
Ramsey stuff runs 25mW into a single whip and those things can throw a signal 3 blocks or more sitting up on a shelf next to a window and it doesn’t seem to be a problem as far as FCC.
Their only concern I would think would be that it’s a cable modulator with easy capably pushing an amp with common connectors being used.
You can always put in-line attenuators too if the signal goes beyond the boundaries of the complex too much.
But here is an online line loss calculator if numbers are a concern.
RFB
Total posts : 45366does 2mW max. i looked at specs of another cable fm modulator and it stated 50dbmv out which converts to 1mW into 75 ohms and 2mW into 50 ohms
Total posts : 45366The posted question was “Is it legal”?…and not “would it be a problem with the FCC.” If I were you, I would run the numbers. Ramsey’s stuff is NOT Part 15 legal at 10mw, let alone 25mw. It may be “OK” with the FCC depending on which inspectors you get, but that doesn’t make it legal, and I wouldn’t want to take that chance. Run the numbers. When you come up with a signal equivalent to 20 – 30 NANOWATTS (that’s 20 to 30 BILLIONTHS of a watt) then you’re reasonably safe. Anyone who’s getting blocks of coverage out of a so called Part 15 FM antenna radiated signal has not been CORRECTLY and ACCURATELY measured, and is not Part 15 FM compliant.
Total posts : 45366the xft40 which IS CERTIFIED goes about 1000ft. covers the whole complex here
Total posts : 45366I don’t believe I said a Ramsey was Part 15 legal, I said apparently the FCC has no issue with a Ramsey 25mW FM 100 and 100-B and FM 25 and 30. Otherwise, they would have been forced to quit selling them A LONG TIME AGO!!
This isn’t to argue what is PRECISELY Part 15 legal. You want PRECISELY Part 15 legal, then go get a PRECISE field strength meter and stand PRECISELY 3 meters from your unit or its antenna at PRECISELY 1 meter off the ground over a ground plane in an open area just like how a PRECISELY Part 15 legal unit is certified, when you can duplicate the lab and field tests PRECISELY as is done and obtained by the testing facility, then you can be rest assured its PRECISELY Part 15 legal.
Blah blah blah!! 😛
I’ve said it many times, FCC goes after complaints and blatant violators..you know the ones who run several or more watts of dirty spiky noisy signals splattering 5 bands with junk and cuss. Rev is taking steps to operate well away from that kind of blatant don’t care could give a rat’s arse approach. That alone, and the way the system is configured and carefully attenuated and arranged as best Rev can do with what he has available to him, will clearly show he is not one of the blatant violators.
Blah blah blah!! 😛
BTW, last inspection my station went through, I was, and still am, running a Ramsey FM 100 through 25 feet of RG 58 into a 1/4 wave GP sitting 8 feet off the ground on a fence pole and the inspecting agent checked it, clearly showed a bit above 250uV and went home happy because it was clean, not throwing watts, jamming up the band, and the programs on it were not curse this curse that dirty foul mouthed stuff. A dose of common sense and good engineering practices goes a long way! Demonstrating those things with how things are set up that can clearly be seen as playing on the right side of the fence is what they also look for.
I think what impressed that agent was the fact I have adequate testing gear to monitor my stations signals and have the knowledge and ability to ensure their proper operation. They like that kind of thing when the station they are inspecting that it’s owner/operator knows what the hell they are doing!
RFB
Total posts : 45366Who makes the xft40? Where can I get info on it? Only info I can find on the web is a listing on Craig’s list.
Only other “certified” Part 15 FM unit I’ve seen come anywhere near the range you claim, are the Decade units, made in Canada. Unfortunately, the stronger Decade units were calibrated to CANADIAN rules before being shipped to the US, which allow about 4 times the signal strength than allowed in the US. Thanks!
Total posts : 45366This might help rlkocher…..
Get a Canadian flag, display it on the front porch, and operate a Decade transmitter under Canadian law!
I’m thinking about flying an Australian flag so I can get an annual license for 26mHz at 1kW.
Why didn’t we think of this before?
Heck, name yourself a Canadian diplomat and call your house an embassy. You’ll have diplomatic immunity for parking your car.
Total posts : 45366i presently have the fms2000 at 88.9 with a T.P.O. of 1mW (50dbmV) (max RF TPO it’s
able to feed to 75 ohms) being fed to
100ft of RG6Qs (-3db) being fed to a F to PL259 adapter into a SO239 to NMO
adapter on an L bracket to which a there is a 19-1/4 inch maxrad whip
mounted.on the coax near base of antenna is a snap on ferrite core to prevent coax
radiation. and mount is on a wood railing about 12ft AGL. presently the thing seems to
about 600ft to grundig (eton) g5 with it’s telescoping whip collapsed and
folded down. i had a 32.8″ whip (1/4 wave at 88.9) in which it went close to 1000ft with grundig and whip on it collapsed.oh yes i have no co channel or 1st adjacent’s at 88.9 here.
Total posts : 45366That sounds like a really cool way to do FM, kc8gpd.
Excellent.
Total posts : 45366i just made a current choke (using instructions found on www) near antenna base in addition to snap on ferrite
Total posts : 45366BTW, last inspection my station went through, I was, and still am, running a Ramsey FM 100 through 25 feet of RG 58 into a 1/4 wave GP sitting 8 feet off the ground on a fence pole and the inspecting agent checked it, clearly showed a bit above 250uV and went home happy because it was clean, not throwing watts, jamming up the band, and the programs on it were not curse this curse that dirty foul mouthed stuff. A dose of common sense and good engineering practices goes a long way! Demonstrating those things with how things are set up that can clearly be seen as playing on
WKID in Clearwater, FL has been running a Ramsey with a Comet 5/8 about 10 feet. Cleared FCC inspection and even had an interview on thier station with the FCC.
Total posts : 45366I have heard this conversation a thousand times before, this is legal this is illegal. Really?? Are we really beating this dead horse again?? AM/FM SW/LW UHF/VHF GHz can all get us into trouble but i honestly think what causes a visit from the oh so scary FCC is COMPLAINTS!
Visit’s are Complaint driven, plain and simple. The FCC does not drive around looking for someone to bust. They don’t have the resources to be everywhere all at once. Can we predict when a nasty neighbor is going to get a bee in their bonnet and call up the FCC?? Nope. All we can do is keep the signal clean and use our best judgment.
Will that new show you are about to air have explicit content?
Hope not! But seriously who hasn’t heard all the “sentence enhancers” at least twice in their lives??As RFB said…
“A dose of common sense and good engineering practices goes a long way! ”Even my Ramsey FM 25 B can be heard at 1/4 mile away with the RF power nearly turned off and a home built folded dipole 12 feet in the air but that is not how i run it.
I usually run the Ramsey at half power and have heard my station at just under a mile with noise on an after market car stereo. If you are concerned with exceeding the limits then the best way to do that would be bury some leaky cable or build a Faraday cage and put your transmitter in the cage because RF Energy passing through even the worst antenna will go where ever it pleases and there’s nothing we can do about that.
Total posts : 45366“Visit’s are Complaint driven, plain and simple. The FCC does not drive around looking for someone to bust. “
I hate to pop yer bubble, but in fact they do. Piracy is a fairly big issue with the FCC. The NW Regional agent that busted Ken Cartright’s KENC AM operation was cruising the dial and thought the signal, which he hadn’t heard before, didn’t match any licensed stations in the area, triangulated and came to find out it was supposed to be a Part 15 operation, but the Hamilton AM 1000 was mounted on and grounded to a 50′ metal tower, plus there were 4 more synced units operating in the community.
True, most violations are the result of complaints, but not all. Plus, there are many times more violation citings in the FM band than AM. Having said that, I wouldn’t let it stop me from experimenting, where on-air transmissions are kept to a minimum, and definitely not for extended periods.
One thing I must know … How is it possible to get 1/4 mile out of a Part 15 FM transmitter operating at the legal field strength limit of 250uV @ 3 meters? … Please explain.
Total posts : 45366“One thing I must know … How is it possible to get 1/4 mile out of a Part 15 FM transmitter operating at the legal field strength limit of 250uV @ 3 meters? … Please explain.”
Specifically and technically and legally, you can’t but it does not mean that such a field strength can’t surprise you just as 100mW AM can surprise you from even a piece of wire strung across the ceiling or a window frame.
Car radios are super sensitive, especially in the FM band and that plays a role as well as environmental conditions and height of radiator.
Sometimes the numbers don’t explain or support what can take place in reality. Thing is…reality can throw it’s own share of surprises too.
RFB
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