Hi all,
Long time Part 15 enthusiast and lurker here... I am using a Drake FMC-1000 FM Stereo Modulator for property-wide (personal use) rebroadcasts of streaming music, audio from my shortwave SDR and police scanner. The Drake has nice clean audio but the RF output is only just a tad above 1mW (+50dBmV @ 75 ohms). I am currently using a 1/2 wave vertical dipole fed with about 15 ft of RG-6 coax.
My issue is I need a bit more coverage of my semi-rural property. While still within line of sight of the antenna the signal fades a bit here and there. Of course these are areas I frequent most often. It isn't frequency related because I have tried multiple vacant frequencies across the band with the same result and it doesn't appear to be multi-path cancelation either. I am fortunate to have 7-10 good vacant frequency choices. I'm looking to add an additional 100 feet or so of coverage.
My choices seem to be 1) improve the antenna or 2) get a higher output transmitter.
Option 1 is limited due to the potential mounting options available. Using a Yagi or other directional antenna isn't a total solution since the low signal spots are not in the same direction. I may be able to add a few extra feet to the antenna elevation but that is also limited.
Option 2 is more expensive but a possibility since I used this transmitter so often and is of value to me.
Any recommendations for me for either option? Thanks!
Probably not what you want to hear but you'll have several comments advising that your setup is most likely over the limit already.
Typical figures of a few nano watts into a dipole is the limit.
Perhaps you could more centrally locate your system on the property to give even coverage all over. Maybe a 5/8 wave ground plane antenna to put your signal down where it's needed as a vertical dipole would have a higher angle of radiation.
Other than that, staying legal makes it tough to cover a large area using FM.
I appreciate your comment which is why I am seeking advice on this forum. I am currently only getting around a 50 ft range from my current setup. I see that a device like the C. Crane transmitter "claims" 45 ft range with their attached whip in their marketing material. My setup must be terribly inefficient. 🙂
sent you an email with some info,,,
What kind of radio are you using to receive your signal? Range (not legality) depends on a number of factors, but mostly that.
The FCC states that you can get up to 200 feet range with a legal Part 15 FM signal on a typical (unspecified specs) radio. Assume a decent portable. It is possible to get 600-800 feet in ideal conditions with a superb radio, such as a sensitive car radio.
If you are only getting 50 feet range with a portable, then it's likely that you have some leeway in improving your signal and still remaining legal (the C Crane has been shown to produce a field strength significantly under the legal limit). Perhaps you're losing a lot with your coax run (if it's not good coax). You could try using a certified transmitter running closer to the legal field strength limit and elevated (such as a Decade MS-100 with is built-in telescopic antenna).
Another approach might be to use a better radio at the receiving end. Doubling the sensitivity of your radio means doubling your range. Since experimental results in varous studies have shown that radio sensitivity amongst consumer portables is all over the map, that might be the best way to go.
I've used several receivers from the AM/FM earmuff style to a GE Superradio II. Obviously, the reception was better with the GE but there was still a noticible signal drop in the same locations as the earmuffs, just not as severe.
I'm going to have to look at why I am only getting the limited range I have. The coax is good so maybe antenna placement is poor. I'll do some more investigative work to see if I can make more sense of it.
Thank you for all the comments and advice. 🙂
Did I miss something here? what kind of antenna are you using with the Drake? What is it's polarization, vertical or horizontal? Polarization could be playing a large role in covering the area you are looking to cover.
Ok My bad it was at the end of the OP sorry about that. hmmm
"I am currently using a 1/2 wave vertical dipole fed with about 15 ft of RG-6 coax."