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In the previous discussion topic thread named “Wired links”, a lot of chatter came about Wilson’s wired repeater system, which uses cables between the repeaters and terminal ends.
In the previous discussion topic thread named “Wired links”, a lot of chatter came about Wilson’s wired repeater system, which uses cables between the repeaters and terminal ends.
However, what if we used some sort of short-medium range Part 15 certified wireless microwave units, i.e., a base station at the TX and receivers at each repeater. Are there any units which can carry the same RF information which is carried in the cables to the repeaters wirelessly with little or no loss?
Total posts : 45366In a different thread I brought up the idea of using fiber optics to transmit the actual output of a Part 15 transmitter to an outdoor antenna, since fiber would not be counted with the 10-feet of antenna. The idea was discussed as being “unknown” as to possibility but certainly worthy of experimentation. Maybe I can find that link.
Total posts : 45366Found it
Total posts : 45366There are spread spectrum microwave units available which provide “transparent” channels for data, video, audio, control signals, etc. It was described to me by a vendor as “what you put in you get out”. Since these handle video it would imply a bandwidth sufficient to handle the modulated AM RF signal.
Before pursuing this approach and the attendant problems of RF phasing and audio delay it may be helpful to back up and view the big picture. If the intent is to increase coverage there are two multiple transmitter approaches:
Two or more on the same frequency.
Each on different carrier frequencies.
I would choose the latter since operation on different frequencies eliminates the need for phase and spacing control and the problems with audio delay. Since there would be no mutual interference the patterns from each transmitter would be predictable. Any sort of simple audio link is all that would be required.
Neil
Total posts : 45366Ken,
The concept you outline is that of a “booster” or “translator”. Boosters are, customarily, on the same frequency as the main/base station. Translators are on different frequencies.
To operate on the same frequency (booster), the exciter (base) would need to produce a clock signal to sync all the repeaters output signals. This is the same concept used for AM/FM broadcast booster systems. The FCC considers each booster/remote transmitter as a separate RF source even though the clock signal runs the remote transmit oscillator. Operating on different frequencies (translator/repeater) is easier in practice, however the use of the clock signal can still used for sync timing (audio and xmtr control).
The problem with using a signal from the exciter and injecting it on air directly at a remote “transmit” site, is that the FCC appears to consider this set up (exciter/remote transmitter) as the use of an external RF amplifier. And under 15.204 external amplifiers are prohibited. Frankly, this part of the rules and what you’re trying to do, don’t seem to have much common ground.
Additionally, using AM for a repeater system signal will produce a higher than acceptable noise level on the remote transmit audio. To produce an acceptable signal to noise ratio for an AM receiver really won’t produce much gain in extending the coverage area in Part 15 service. Part 15 FM repeater systems have very limited effectiveness in extending coverage because of the allowable field strength and distance.
Of course, the use of Part 15 5.xx GHz equipment could be used as a distribution system for control and audio with the use of an encoder/decoder pair. Essentially, this is a Wifi STL system. Trango is well known for there Part 15 unlicensed wireless systems.
I am not trying to be difficult. I am just trying to think like an FCC inspector and give you my impressions.
Total posts : 45366Hi Neil,
I certainly understand where you’re coming from, and it’s probably my only choice at the moment, but I don’t relish the idea of listeners having to switch frequencies, especially if they’re driving (auto radios are the best receivers), so in the near future, I would rather go through the trouble and moolah to get my content on one reliable frequency.
If I can put together the software to get something like, say, a few Ubiquiti Bullets with dish antennas to get a couple more transmitters sync’d, then that’d be the berries.
Total posts : 45366Ken,
I understand. When I posted I had in mind stationary listeners.
Unfortunately, if the transmitters use the same frequency the mobile listener will move from the peaks to the nadirs of signal strength due to mutual interference but maybe a very good AVC in the receiver will mediate this. This is probably less of a hassle than retuning every thousand feet or so.
Neil
Total posts : 45366The committee approach to problem solving can be wonderful when each member is genuinely devoted to doing everything possible with available resources, and that’s what’s found here at Part15.us
This problem of applying part15 tools to blanket a larger area than can be covered with only one transmitter is on the top ten list of interesting projects.
So I wondered what could be learned by comparing with full scale licensed transmission, and I wonder if there are any cases where full power transmitters on the same frequency are synced together to double the coverage area?
Boosters and translators have already been discussed, so what about full power syncing of more than one transmitter?
(I asked the same question twice for emphasis).
Total posts : 45366First of all, FM boosters can have up to 20 percent the output power of the main transmitter. For a 100 KW Class C FM, the booster could potentially use a 20 KW signal. That’s pretty much full power. The booster is on the very same frequency as the main. Most of the boosters licensed today use a digital timing or clock signal either generated by GPS or by a timing generator in the main exciter and transmitted to the booster via the main’s sub-carrier. No booster is allowed to have output power that would allow its signal to extend beyond the main transmitter’s 1 mv./60dbu contour. These boosters can not extend the coverage area. FM boosters are used to provide signal/service where the main signal is very weak due to terrain or some other kind of signal shielding.
On the AM BCB, I am not aware of any full powered synced transmitters licensed for operation. However, there have been experiments done with boosters and shortwave systems. These AM and SSB systems also require a clock signal to sync local oscillators.
Total posts : 45366Allow me to introduce the king of AM BCB multi-transmitter networking; at least the most published. Most of his network appears to be wire/internet linked. However, he is investigating other options. Liberty1640 in Sioux Falls/Aberdeen, SD., Omaha, Neb. and Austin, Tx. is a great example of developing a great plan and then build and change as you go. This Part 15 radio broadcaster is growing to different communities and different states. He obviously has a vision and is able to communicate this to his listeners. Here is the some what dated information on this effort.
Station: Liberty Radio
Location: Sioux Falls, SD
Date Launched: September, 2008
Frequency: 1640 KHz
Transmitter: Rangemaster (x3)
Format: GCN Net, 1920’s & Motown
-courtesy of hobbybroadcasting.comLiberty1640 website: http://www.liberty1640.com
The local network uses more transmitters now and has a more extensive program offering.
Recently, the FCC visited, due to a complaint of a disgruntled political opponent. The ground system was modified and he’s back at it. This challenging situation is repeated weekly all across the country between Part 15 proponents and opponents, and the government.
With the help of Keith Hamilton, this operator is moving forward toward syncing transmitters using GPS to supply the transmitter’s local oscillator clock signal.
And finally, he asks his listeners and supporters to help financially to support his stations. He appears to have success in this area. My guess is, he keeps going until he gets the support he needs and then builds the next station. Kudos. Hang in there.
This guy is a great example of what an operator can do. For him, Its more than a hobby.
Total posts : 45366Thank you, Marshall Johnson, Sr., for always pointing the way on some of the esoteric issues that arise regarding part 15 radio. The example you gave of synced FM stations was exactly what I wondered about, and I think your underlying inference was that there is no reason it wouldn’t work for AM radio.
A very interesting theoretical example comes to mind. In Missouri there are three 5kW stations on 1550 kHz (daytime power). It is unusual for so many station with high power to be so close together. The cities are Cape Girardeau, Springfield and Kansas City. Now let’s imagine that a sole owner controlled all three. You’d have a perfect candidate for inter-locking (syncing) those stations.
Now, a seeming change of subject, actually relates to the spirit of the discussion. I do believe that the part 15 rules as they apply to intentional radiators were intended to allow private individual persons to possess and operate miniature transmitters. But I am sure the strict technical limitations within the rules were intended to disallow any form of public wide broadcasting. The fact that so many people are struggling to expand what can legitimately be done is a perfect example of inventiveness and creativity alive and flourishing in the US.
The Sioux Falls, SD, station is well worth watching for their innovations, and we appreciate your pointing them out. I think purchasing a Rangemaster through them is helpful to their effort.
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