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For those that are less technically inclined (at least with transmitter building and electronic components, etc.), there is an interesting item available on e-bay. http://www.ebay.ca/itm/SHORTWAVE-LOW-POWER-RADIO-TRANSMITTER?item=230901912860&cmd=ViewItem&_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D1%26po%3DLVI%26ps%3D63%26clkid%3D5365802891290202920
This is a low power (100mw), pre-built, shortwave AM transmitter that is capable (according to the builder – I e-mailed) of operating between 10 and 20 Mhz. It comes with 2 crystals, but if you replace one with, say, 13.560, it will work nicely. Part 15.225 states that the maximum field strength in the 13 Mhz ISM band can be no greater than 10,000uv/m at 30 meters, so I don’t know if the 100mw is too much, or too little, but if it’s too much, you can always attenuate. It doesn’t look like there are any antenna restrictions in that band.
I’ved ordered one, but he has a few available. Should be interesting to experiment with.
Total posts : 45366That is a very interesting item, Artisan Radio, and I have some information to add to yours.
The FCC rule 15.255 was updated at some point to allow more power at 13.560mHz.
15.225 (a) The field strength of any emission within the band 13.553-13.567mHz shall not exceed 15,848 microvolts/meter at 30 meters.
In connection with our Big Talker shortwave transmitter builder’s project member PhilB was kind enough to calculate some antenna and power level projections, linked here
Total posts : 45366100mW is way too much even into a short vertical without loading. phil states 5mW input into a 1/4 wave for 16k uV/m @ 30m
Total posts : 45366In some ways, this is all good.
I was planning on using the transmitter on my Comet CHA-250 vertical, which is definitely a compromise amateur radio antenna. It is continuously tuned across the HF spectrum (including the ISM frequencies) but is also less efficient than a quarter wave antenna. Probably on the order of 6-12db, depending on the frequency. I did a quick calculation, and assuming 5mW is the upper boundary of input power for a 1/4 wave vertical, you would need an antenna inefficiency of -13db (as approximately compared to that 1/4 wave antenna) to get the legal field strength. My antenna most likely isn’t THAT bad (at least, I don’t think so, I do get out and make contacts), so I’ll have to look at ways to 1) either attenuate the signal into the antenna or 2) reduce the stated input power of the transmitter.
Total posts : 45366does Canada have an equivalent to 15.225 allocation in that part of the band
Total posts : 45366Yes, Section A.26 in the RSS210 circular (equivalent to Part 15, more or less) restricts field strength in that band centered around 13.560 as 15,848 uv/m at 30 meters. Other frequencies around that can also be used, but allowable field strengths are much less – in the 300uv/m at 30 meter range.
Total posts : 45366By the way, my home built 13.560 MHz
transmitter works great, but physically –
there is a problem – – when I built it,
I just kept adding pieces onto the right
side of what was already there. I had to
build large, because of my eye issues.So I’ve got a transmitter that’s about 18
inches long and about 3 inches wide.
And the modulator is hanging off of
one side. Any enclosure would look
like a condo with a back deck. I suppose
I could add a driveway and put some little
“Matchbox” cars on it.Anyway – this looks like a really really nice
transmitter. (I mean the one that is the topic
of this thread.)Bruce, from past stations, MICRO1700 and the
Dog Radio Group
Total posts : 45366I think transmitters that are 3-inches wide and 5-feet long would go well in an N-scale model railroad setup, where a 10-foot antenna would be the equivalent of a 1,000-foot tower.
You could have a miniature FCC which would allocate frequencies for your little train station town, including daytimers and nighttimers.
The full sized world of adult living has fallen into disrepair, so why not escape into a mini-world of imagination? I have.
Total posts : 45366I’ve been in touch with the builder, and the transmitter can run on 9 volts with reduced power output. I guess I’ll just have to experiment when it arrives.
Total posts : 45366Also: To Robert, KC8GPD – I love the picture
of your Field Strength meter.And to Carl – my brother once had some great
model train set-ups. I always wanted to make a
little model of a 250 watt AM daytimer to put in
his little town, complete with tower and red lights
at night (whatever that means – I guess when the
lights are turned off in the room.)It never happened.
Bruce, Past Part 15 Guy, and hoping to do it again
someday.
Total posts : 45366thanks that is my FIM a Nems Clarke 120E covers 540-1600khz
Total posts : 45366Bruce’s story about his foot and a half long board reminds me of a couple of things. First, Bruce, I appreciate and understand why you built it this way and it is more important to do this than to worry about small size and not do it at all. Do what works for you.
In general, when I attempt to make a prototype the finished unit the result is failure in terms of “packaging” and appearance. It is better to use the prototype as a parts source and when the operation of the circuit is up to snuff then rebuild it on a new board. I have also learned to build the circuit then find a box to put it in, not the other way around. If I pick a box first things don’t seem to fit after the circuit is built.
The other thing the “long and narrow” board brings to mind is a story about a pilot and co-pilot who found themselves in a situation requiring an emergency landing. A runway was sighted but it was very short. They both sweated and strained to bring the plane safely down and after they came to a stop inches from the end of the runway they reflected on the experience. The pilot remarked “That sure is a short runway, must only be a 100 yards or so long.” The co-pilot looked side to side and said “Yah, but it must be a mile wide!”
Neil
Total posts : 45366I just bought the last one. Sorry ’bout that!….but I’m sure he’ll be building more.
Found the antenna/power/field strength link most interesting, but think we might be missing the boat on this.
On the SW bands, we’re usually looking for skywaves. Lower radiation angles are better, of course, but we’re still after skywaves primarily. Since the field strength measurements were taken at ground level, isn’t it possible…or even likely…that a measurement taken 30 meters away from a dipole, AT THE ANGLE OF MAXIMUM RADIATION, would be MUCH HIGHER than the ground level reading? Makes sense to me. But how could you possibly measure it? You’d have to have the meter mounted on top of a 90 foot pole! Unless you have a 90 foot building or tower within 100 feet or so of your antenna to stand on, you can’t measure the signal at that point. Do you think the FCC would bother bringing in a helicopter in this case?
I’m definitely going to try a dipole with my transmitter, but I also have a 20 meter Isotron I should be able to re-tune and play with. (It’s only 2 feet long! Theoretically, it shouldn’t do much more than a dummy load!) It to, will be mounted 20 or 30 feet up, but any measurements will be taken on the ground. Should be interesting!
Total posts : 45366I am listening on 13.560 MHz using an outdoor antenna and at present (2:28 AM EST) it is very quiet. Very little background noise (less than S1). When you folks get on the air announce it here and I will listen for your signal. Given the propagation on this band anything is possible.
Neil
Total posts : 45366Sure will, Neil. I’m looking forward to 20 meter-like proposgation; you always hear about hams going hundreds of miles on a milliwatt or so. Mind you, that’s usually CW, but I’ll settle for an even hundred miles AM 🙂
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