Insane Ideas

Well.  Yeah, we've talked about this before.

Sort of.  The houses in my last neighborhood

were PACKED together.  The properties were

very "thin" (no side yards) but went way way

back.  My old back yard went back more than

150 feet.  The idea was to put an FM transmitter

in the front yard, way way back in the back yard,

and on each side.  (Left and right.)  I guess this

is not really exactly like your idea - but it still

uses multiple transmitters to attract attentiion. 

I think this would be a very VERY hard thing to do.

It's fun to think about, though. 

Bruce, Mon. Stn., CT

One I would be curious to see is a test setup with same channel part 15 transmitters to determine spacing and interference between them. Let's call first contour easily receivable and second as barely receivable. Given minimal overlap on second, I would think that there would be no interference in first contour. I'm guessing at such low EIRP they could be spaced pretty close.

Or did I completely miss the point and ramble? Hehe, sorry if that's the case.

Mr. KenFisher you got the idea.

It can come in different variations, such as side-by-side frequencies OR transmitters on the same frequencies at far distances.

Let's load the place with Part 15 transmissions and take over the empty slots!

Part 15 men reproduce wildly and our off-spring set up transmitters and their off-spring.

The FCC is impotent to our reproductive thrust.

Ubiquiti makes some competitively priced 802.11 gear on both 2.4 and 5 ghz. Point to point at 2 to 3 miles isn't out of the question depending on terrain. I could see a wireless network infrastructure serving as stl and remote operation. A few well placed transmitters could cover a lot of population with wired networking remotes filling in the gaps.

Noted: I have mixed feelings on just using wired network for all locations. Mostly because it presents a single point of failure in case of natural emergency. Pushing the value of community radio as an emergency preparedness communications tool might lend validity to such a project. Maybe get a few hams or the local REACT people involved. Is react still around even?

I tried to put a little solar powered

Part 15 FM transmitter in the second

story of a friend's garage.  You know,

just a little experiment, really.  It would

either run it's own programmiing or

repeat my other transmitter.

He's a GREAT guy, and he's an engineer,

so I figured he would be more likely

to say yes.  But, but didn't really understand,

and he said no.  Like I said, a really great

guy - so I didn't press the issue. 

It's easy to make the hardware.  It's

difficult to find a place to put it. 

Bruce, Mon. Stn.,CT

I would like to install a transmitter in your daughter's bedroom.

My opening post in this thread talked about placing transmitters on side-by-side frequencies covering a batch of open frequencies, sort of like laying a six-lane highway to replace one-lane.

I have decided to set up an experiment, but not with nine transmitters, just simply three transmitters. That will be enough to demonstrate the concept in practical terms.

The frequencies will be 1640, 1650 and 1660 kHz.

The audio will be fed by hard-wire from a central point so that the audio will synchronize on all three transmitters.

Physical placement of the transmitters/antennas is the unknown factor going into this venture. If they are placed in exactly the same location the transmitters and their antennas will inductively feed RF into each other which can cause distortions, so I expect.

Maybe a triangle with transmitter # 1 in the rear-yard, transmitter # 2 in the front-yard and transmitter # 3 in the side yard.

The advantage will be a very wide signal on the X-band, wider than any other station in town.

Predictions? Advice?

No idea what to expect. It should be noticeable on a receiver with slide rule tuner. Possibly not so much on a frequency locked. I guess adjacent channel could contribute, but might just interfere.

Interesting experiment.

My first method of placing three transmitter/antennas in different locations is the most simple way to try the idea of "tri-jacent" broadcasting (3 adjacent channels).

But it would also be fun to plan some kind of "combining" or "mixing" all three transmissions into a single antenna. Not so easy to do without sacrificing precious millwatts.

Perhaps the combining could happen prior to the final RF amp stage... since we only plan a single audio feed for all three frequencies the final RF amp could simultaneously modulate all channels.

I guess the total input to the final RF amp would be 300 mW, since each frequency is allowed 100 mW.

... Perhaps the combining could happen prior to the final RF amp stage... since we only plan a single audio feed for all three frequencies the final RF amp could simultaneously modulate all channels etc.

I can never decipher the technical accuracy Carl Blare thinks/hopes really applies to his posts.

In this case, he and those who might be tempted to believe the content of that post would do well to investigate further.

Details on request.

Rich, I will welcome discussion of how to or why not to pursue my idea of side-by-side-on-the-dial transmission of Part 15 AM medium wave signals, possibly using combining to funnell 3-separate transmitters into a common output stage/antenna.

Will enjoy your views.

Carl Blare posted:

... I will welcome discussion of how to or why not to pursue my idea of side-by-side-on-the-dial transmission of Part 15 AM medium wave signals ...

Maybe you didn't notice, but my reply was directed at, and quoted this part of your previous post in this thread:

... the combining could happen prior to the final RF amp stage... since we only plan a single audio feed for all three frequencies the final RF amp could simultaneously modulate all channels etc.

A transmitter using a single Class C/D/E r-f amplifier driven by three r-f carriers spaced 10 kHz apart, and able separately to amplitude-modulate each of those carriers synchronously from one audio source and with sufficiently low r-f intermodulation would be a rather extreme technical and economic challenge.

Without the needed performance, this system could produce mutual interference that could reduce the useful coverage areas for the 10-kHz-carrier-spaced AM signals that any one of them could have as a legal, standalone system -- as well as to cause interference to other users of the r-f spectrum.

That answer gives me some relief, since I was worried that my fundamental idea of a three-carrier-lane-highway on three side-by-side frequencies with a single synchronized audio source might get dismissed as ridiculous, for some reason. But that's not what happened.

All right, my thoughts about "mixing" or "combining" grew out of articles I read about "70-transmitters atop the Empire State Building combined into a single antenna larger than King Kong... (slight exageration)."

I am dimly aware that combining at RF frequencies is more complex than simply using an audio-mixer circuit with RF signals.

But you didn't say it was impossible... just an "extreme technical and economic challenge."

So, we resort to Plan A, three individual transmitters separated by distance and hard-wired with a single audio source. That's good enough to test the "wide signal" idea, maybe? 

There are such things as co-located AM's that share a common antenna using a combiner or diplexer.  But at our power levels most of that precious little signal would be lost in the process.

Kintronic Labs offers a complete line of transmitter combiner/ paralleling units to permit the synchronous operation of two transmitters of a similar or equivalent design.  In this case the idea is to run two transmitters on the same frequency perfectly synchronized.

A diplexer may be used by a broadcast station transmitting on several different frequencies at the same time using the same antenna. The use of the diplexer enables a single antenna to be used, while preventing the output from one transmitter being fed back into the output of the other.

But again, at our power level I think most of the signal would be lost in the process.