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Cache Idea


Zosimos
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Hi,

 

I have an idea for a themed mystery cache that would fit the surroundings of a local area here. It would involve transmitting a series of numbers on a shortwave radio frequency, and I would provide a receiver at a location so the "spy" would receive the numbers and would be provided a "one time pad" to decrypt the secret message (i.e. a numbers station).

 

I was wondering how difficult it would be to do this as I don't have experience with ham radio. Do I need to acquire a license to broadcast on shortwave? I think I read the FCC doesn't regulate if it is within 300 feet, but if it is longer they do? Is that correct? In fact, I'm not sure ham radio and short wave are the same thing. True?

 

If there are any radio enthusiasts out there who can comment on the feasibility of this idea I'd greatly appreciate it including recommendations for equipment needed if it could be pulled off.

 

Thanks!

Edited by Zosimos
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This is a cool idea. Translation: I might steal it!

 

If was going do to that, I would not leave any theft-worthy receiving equipment at the site -- I would use already-available technology like CB or FRS.

 

My question would be whether I'd be allowed to leave an automated device transmitting a looped audio track on those public frequencies?

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There are low-power FM transmitters that are used by people who set up elaborate Christmas light displays, with the lights synchronized with the music being broadcast on the FM transmitter. They don't require a license to operate, and don't require any special equipment to receive. Something like that might be a better choice for someone who doesn't already have experience building and operating ham radios.

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Considering you probably want a audio signal you want to stay away from certain transmitters. I don't think you can arbitrarily transmit on HAM radio frequencies without a license. I should know because I have one but I just don't remember the details. You can get low power FM transmitters in kit form for under $20. Here is a link to one: http://www.canakit.com/universal-fm-transmitter-with-mic-and-line-inputs-kit-ck108-uk108.html and another link to a voice playback module: http://www.ebay.com/itm/WTV020-SD-Voice-Module-MP3-Sound-Module-U-disk-Audio-Payer-SD-Card-For-Arduino-/121140012107?_trksid=p2054897.l5670 You would also need some sort of microcontroller to make everything work. It's not a project for the first timer.

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This is a cool idea. Translation: I might steal it!

 

If was going do to that, I would not leave any theft-worthy receiving equipment at the site -- I would use already-available technology like CB or FRS.

 

My question would be whether I'd be allowed to leave an automated device transmitting a looped audio track on those public frequencies?

I know that you can't put loop recordings on CB or FRS frequencies.
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Considering you probably want a audio signal you want to stay away from certain transmitters. I don't think you can arbitrarily transmit on HAM radio frequencies without a license. I should know because I have one but I just don't remember the details. You can get low power FM transmitters in kit form for under $20. Here is a link to one: http://www.canakit.com/universal-fm-transmitter-with-mic-and-line-inputs-kit-ck108-uk108.html and another link to a voice playback module: http://www.ebay.com/itm/WTV020-SD-Voice-Module-MP3-Sound-Module-U-disk-Audio-Payer-SD-Card-For-Arduino-/121140012107?_trksid=p2054897.l5670 You would also need some sort of microcontroller to make everything work. It's not a project for the first timer.

 

I'm not really interested in building anything too complicated. I'd prefer to do this with a turnkey solution, if possible. I was thinking of using a mini transmitter (http://www.amazon.com/dp/B00GXNRETS/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=QMZSLCXCJP4&coliid=I18YBCTE1U8NDM) connected to a mini MP3 player that would play a loop that would broadcast the "message" powered with a solar solution.

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I'm not really interested in building anything too complicated. I'd prefer to do this with a turnkey solution, if possible. I was thinking of using a mini transmitter (http://www.amazon.com/dp/B00GXNRETS/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=QMZSLCXCJP4&coliid=I18YBCTE1U8NDM) connected to a mini MP3 player that would play a loop that would broadcast the "message" powered with a solar solution.

 

You are not going to get a great range on that. I'm guessing not even 30'. They are designed for in car use to go from your phone the the radio. Search www.amazon.com or www.everbuying.com for "car mp3 player fm transmitter" for something closer to what you are looking for.

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You are not going to get a great range on that. I'm guessing not even 30'. They are designed for in car use to go from your phone the the radio. Search www.amazon.com or www.everbuying.com for "car mp3 player fm transmitter" for something closer to what you are looking for.

 

I was thinking I would hide the transmitter very close to the location where they would be directed to receive the message, like perhaps in the tree above the container where I hid the radio for them to use? The transmitter would be cammo'd so visitors wouldn't even know the transmitter was above them.

 

I guess this circles back to my original question as to my need for a license to transmit anything with a long range. And if I go with something that transmits with a longer range, what would that equipment look like? I'd rather have something that transmitted on a shortwave band to make it seem more authentic.

Edited by Zosimos
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The concept of the cache is no different than a Chirp or any other beacon

 

I am unfamiliar with beacon caches. What type of equipment do you need to receive/transmit "beacons?"

 

Beacon caches (an attribute, not a cache type) were introduced when Garmin introduced the Chirp. The Chirp is a low power transmitter that uses the ANT+ protocol to broadcast a short message, and can operate for a year or more on a coin sized battery. Only some Garmin GPS receivers support Chirp. The Beacon attribute is meant for any cache that uses wireless transmission as part of the search process.

 

http://support.Groundspeak.com/index.php?pg=kb.page&id=303

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Beacon caches (an attribute, not a cache type) were introduced when Garmin introduced the Chirp. The Chirp is a low power transmitter that uses the ANT+ protocol to broadcast a short message, and can operate for a year or more on a coin sized battery. Only some Garmin GPS receivers support Chirp. The Beacon attribute is meant for any cache that uses wireless transmission as part of the search process.

 

http://support.Groundspeak.com/index.php?pg=kb.page&id=303

 

I see. Interesting, but since it's limited only to those with certain Garmin devices it doesn't seem very practical for my purposes.

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I see. Interesting, but since it's limited only to those with certain Garmin devices it doesn't seem very practical for my purposes.

 

Agree. While I use a Garmin device myself, I wouldn't put out a Chirp only cache since it would exclude too many cachers. The FM transmitter idea is probably the easiest.

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I use this http://www.canakit.com/universal-fm-transmitter-with-mic-and-line-inputs-kit-ck108-uk108.html FM Transmitter on my cache Cache 9 from Outer Space.

 

It works great. I took an old MP3 player and hooked it up to the line-in input, and set the MP3 player on loop mode.

 

I modified the transmitter and the MP3 player to be powered from an AC-to-DC adapter "wall-wart".

 

You appear to have done exactly what I want to do! So, how hard is it to build that kit? The picture resembles a card I'd need to solder on to a motherboard or something! Does it come with an external housing unit? Would it be easy to modify to be powered using a mini solar cell? I was looking at something similar except to transmit on AM Frequency (1/4 mile rang).

 

http://www.tequipment.net/RamseyElectronicsAM1C.html

Edited by Zosimos
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I use this FM Transmitteron my cache Cache 9 from Outer Space.

 

It works great. I took an old MP3 player and hooked it up to the line-in input, and set the MP3 player on loop mode.

 

I modified the transmitter and the MP3 player to be powered from an AC-to-DC adapter "wall-wart".

 

[edit to finish the post]

Here is a link to a video of how one guy used a low-power FM transmitter. His setup used AC power and was in a building at GC for the first stage.

 

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