Revised idea for a mystery cache involving radio

[+nekom]

I had been thinking of a puzzle cache involving radio for awhile now. Initially I thought it would be impossible to do what I had planned, figuring instead on including an audio file on the cache page and/or a cd, cheapo MP3 player in a stage, or something to that effect.

 

After some research, however, I am reasonably convinced that I could mount a very low power transmitter at my house which would be able to reach the planned cache area while still keeping within FCC (Federal communications commission, who regulates radio frequencies in the United States) regulations. So here are my questions:

 

1. First and foremost, is there any reason this would violate GC guidelines?

2. Would it be best to hide a stage with a receiver (and note the type of batteries required in case it goes dead), OR to list it as a difficult 5 because special equipment (a device capable of receiving this frequency) would be required?

 

I think this has the potential to be an AWESOME puzzle even though it would be a lot of work on my part and some minimal expense as well. I am not aware of a cache like this, though there may very well be one.

[+briansnat]

There is nothing that on the surface looks like it would violate the guidelines.

[+cw1710]

You can get FM transmitters on the internet fairly cheap. I think it would make for a fairly neat cache depending on where you live. I always feel a little funny going to neighborhood caches. Maybe they just drive to coords on the street and listen to the proper frequency to get a clue or the coords but dont have to get out there. The only thing is that this might get your neighbors suspicious if you dont explain it to all of them. The traffic coming and going in short time periods may lead them to believe there are drug transactions going on (even though no one ever approaches the car people just dont use logic these days).

[+TeamPatchwork]

GC12EAW is a cache based on the idea you've presented, and it's a well done cache...so there is at least one out there.

 

There are a number of unlicensed radio services (MURS, FRS), or, if you have the interest, you could study for your ham radio license and do some REALLY cool stuff with it!

[+BBWolf+3Pigs]

Cache 9 From Outer Space is my cache that uses an FM transmitter and an MP3 player. If you want, contact me via my profile for more info.

[+nekom]

GC12EAW is a cache based on the idea you've presented, and it's a well done cache...so there is at least one out there.

 

There are a number of unlicensed radio services (MURS, FRS), or, if you have the interest, you could study for your ham radio license and do some REALLY cool stuff with it!

 

The two bands I was considering were FRS and CB. FRS seems ideal because the range is limited (due to very low power being used) to only a mile. It's not likely to interfere with anything or even be noticed unless somebody happens to have a scanner monitoring them. I could probably do CB as well if I didn't use 9 (emergency use only) or 19 (truckers) but the only CB I have pushes 6 watts so it carries for at least 5 miles, on a good day probably 20 and that's not even accounting for skip which under the right (or wrong depending on how you look at it) conditions can travel hundreds of miles.

 

My idea would require constant 24/7 transmission because I have no idea when someone would be seeking the cache and I'm pretty sure caches need to be constantly available per the guidelines (i.e. can't say you have to call first, etc) so as such it HAS to be very low power, JUST enough to reach the target site and low enough not to cause interference with anything else. FRS seems to fit the bill.

[CoyoteRed]

I've thought about a cache like this. My conclusion was use FM. By far, more people have a FM receiver than any other radio--there's probably one in your car. Next, it would be mounted near a parking lot so you can get your car near it. This was a night cache so it would start transmitting around midnight and go until the batteries are dead. The next day a solar cell would charge the batteries.

 

The limited range of a few hundred feet would force the seeker to one parking lot. You can make a day time transmitter with just a solar cell. Depending on the solar cell size and power of the transmitter you could make it so only sunny days will transmit.

 

Look into BASIC stamp computers. These are neat in that you can control all sorts of the things.

[+WRITE SHOP ROBERT]

As one who uses CB radio, I'd recommend not going that route, just because you never know what channel people might try to use, us truckers often switch to other channels for extended conversations(to keep 19 clear for others to use) Depending on your transmission level this could either hog the channel, or be overpowered by other users.

 

If you want the finders to listen to your broadcast AT the Cache site, could you modify a wind up radio to receive only one frequency? No batteries needed then.

[JohnX]

Monopolizing many "no license required" radio frequencies with constant transmission is forbidden by the FCC. If you don't know where to find this information, then you have no business doing it.

 

From experience, you don't just buy a FM transmitter, a battery, a audio device, some solar cells and solder them together to make a automated radio transmitter. There are a lot of things to consider that many people would not even know about. But hey folks, if you don't believe me, give it a try and post your results. I might learn a few tricks from your success.

[+BBWolf+3Pigs]

From experience, you don't just buy a FM transmitter, a battery, a audio device, some solar cells and solder them together to make a automated radio transmitter. There are a lot of things to consider that many people would not even know about. But hey folks, if you don't believe me, give it a try and post your results. I might learn a few tricks from your success.

 

What kinds of things should one consider? Are you talking about technical hurdles or other things?

[+WRITE SHOP ROBERT]

Monopolizing many "no license required" radio frequencies with constant transmission is forbidden by the FCC. If you don't know where to find this information, then you have no business doing it.

 

From experience, you don't just buy a FM transmitter, a battery, a audio device, some solar cells and solder them together to make a automated radio transmitter. There are a lot of things to consider that many people would not even know about. But hey folks, if you don't believe me, give it a try and post your results. I might learn a few tricks from your success.

There must be ways of doing what the OP wants though...real estate agents can set up listing info that can be listened to while parked in front of the house...or at lease they HAVE done that, maybe it was illegal?

 

From your post it sounds like you're knowledgable on the subject? Rather than just stating "If you don't know, you don't belong to our group" maybe you could point to where we can learn?

Edited April 2, 2010 by WRITE SHOP ROBERT

[+BBWolf+3Pigs]

The FCC Webpage that describes unlicensed FM radio transmissions.

[+WRITE SHOP ROBERT]

Thank you. There's some good info starting there.

 

From that "Part 15" bit, it looks like a range of 200 feet if the maximum allowed? I guess that's a good starting point to working out the solution.

Edited April 2, 2010 by WRITE SHOP ROBERT

[+BBWolf+3Pigs]

Thank you. There's some good info starting there.

 

From that "Part 15" bit, it looks like a range of 200 feet if the maximum allowed? I guess that's a good starting point to working out the solution.

 

And some more. Looks like htere is apower cut off (plus the max range) to operate unlicensed.

[JohnX]

The FCC Webpage that describes unlicensed FM radio transmissions.

Thank you BBWolf for demonstrating what a few moments with a search engine can do. (On a side note, considering the recent weather in Rhode Island, I hope you searched on "How to swim.")

 

It is not my intention to list the technical considerations in building a radio beacon. I just offer a warning that it is not as simple as it seems. I suggest a good starting point would be to figure out the power requirements of your system and go from there.

[+WRITE SHOP ROBERT]

Wow...I'm feeling so much like my first winter driving a Truck...whan asking advice on how to keep the trailer brakes from freezing overnight I was told "If you don't already know that, you shouldn't be driving"

 

Is it sooo hard to just say...

 

"You should read up on the FCC rules before cunstructing such a thing"?

[JohnX]

Monopolizing many "no license required" radio frequencies with constant transmission is forbidden by the FCC. If you don't know where to find this information, then you have no business doing it.

 

Rather than just stating "If you don't know, you don't belong to our group" maybe you could point to where we can learn?

Hey Write Shop,

 

Please don't use quotes to make it seem that I said "If you don't know, you don't belong to our group". I did not say that and for you to even hint that I did is a dishonest and cheap shot that influences my opinion of you.

 

If you want to learn just type "www.google.com" into your browser bar. There is a whole big world out there.

 

J.X.

[+BBWolf+3Pigs]

The FCC Webpage that describes unlicensed FM radio transmissions.

Thank you BBWolf for demonstrating what a few moments with a search engine can do. (On a side note, considering the recent weather in Rhode Island, I hope you searched on "How to swim.")

 

It is not my intention to list the technical considerations in building a radio beacon. I just offer a warning that it is not as simple as it seems. I suggest a good starting point would be to figure out the power requirements of your system and go from there.

 

I used a Canakit UK108 FM transmitter, a cheap MP3 player, and two AC to DC wall-warts. One I wired into the FM transmitter in palce of the batteries. The other I wired into the MP3 in place of the battery. Since most MP3 players with rechargable batteries do not play when being charged, I used one that took a AAA, but wired in the wall wart to the battery leads.

 

This set up has been working quite well for almost 2 years. Only issues havebeen when the building it is in gets a power interuption (storms, etc). I have to go and turn the MP3 player back on.

[+WRITE SHOP ROBERT]

 

Hey Write Shop,

 

Please don't use quotes to make it seem that I said "If you don't know, you don't belong to our group". I did not say that and for you to even hint that I did is a dishonest and cheap shot that influences my opinion of you.

 

If you want to learn just type "www.google.com" into your browser bar. There is a whole big world out there.

 

J.X.

My apologies. I've dealt with plenty of groups of people who use statements like that to insinuate that they are better than the people who are trying to learn. It just creates a defensive reaction in me. I was not trying to misrepresent what you wrote, only demonstrate the way it reads to me. Maybe I'm reading too much into it. Again, My apologies.

[+WRITE SHOP ROBERT]

Another note on a project like this...PLEASE...Make sure that you're not making anything that would be mistaken for a bomb(either by it's design OR it's placement). We have enough trouble with the bomb scares even without all the wiring in these things.

[+Kevin and Lori in the sticks]

Ever see those xmas light displays that are programed to react to music. Those involve using a FM transmitter, and I'm sure they are within FCC rules for unlicensed transmitters.

[+BBWolf+3Pigs]

Another note on a project like this...PLEASE...Make sure that you're not making anything that would be mistaken for a bomb(either by it's design OR it's placement). We have enough trouble with the bomb scares even without all the wiring in these things.

 

Mine is actually located in a park building, with permission from the park staff (who just happens to be a geocacher!)

[TheHunterSeeker]

Cool idea

[CoyoteRed]

Another note on a project like this...PLEASE...Make sure that you're not making anything that would be mistaken for a bomb(either by it's design OR it's placement). We have enough trouble with the bomb scares even without all the wiring in these things.

Disguised as a bird house or similar it a good start. A solar panel on the roof should hide it okay, but from a distance. You can angle the roof for your latitude. The box hides the innards. Only a little wire would hang.

 

If it's near something man-made an electrical box should be fine. You see similar things in rural areas with antenna and the whole nine yards. Yours will blend right in.

[+BBWolf+3Pigs]

Cool idea

 

This is the one I used. Transmits a good signal out to about 100'.

[JohnX]

This looks interesting:

 

Audio Module

 

Found in less than 3 minutes on Google.

[+chachi44089]

You will be limited to only about 25 milliwatts.a few hundred feet.FM.and only on a "empty"frequency.No CB,of FRS.you would block legal transmissions on these channels if you did.Many real estate agencies use "micro-watt"FM transmitters to advertise home sale descriptions when you pull up in front of the house.These transmitters are legal to use if you stay within the FCC rules for use.I have a low power FM transmitter that I use to "broadcast"my serious radio player over my property so I can use any old FM radio to listen in my barns and such.Just read the FCC rules and build it,and broadcast from your home.Short distance.Hobbytron sells nice low power AM and FM transmitters that would work fine.

[+Minimike2]

Here is mine - GC1XGTH

 

A simple MP3/FM transmitter with my recording playing on a continuous loop. Cost about $20 for the unit and an AC adapter to an automobile cigarette plug. reaches under 100 feet.

[+nekom]

First of all, THANKS EVERYBODY for the posts here and a few private messages that really steered me right. It's beginning to look like the best bet is going to be an unlicensed (but FCC legal) AM transmitter, the kind that they use for real estate, is going to best fit the bill. It's going to push the range but I believe it will work as long as I can slide it to a frequency not used by any nearby commercial AM station.

 

Now I don't know if a car stereo will be sensitive enough to pick this up or if I'm going to have to throw a cheapo radio in a stage of the cache, but I believe that this is going to work. I'm so confident that I've already placed the final and put a bid on ebay on a transmitter. I hope my `Lincolnshire Poacher' works out well.

[+chachi44089]

First of all, THANKS EVERYBODY for the posts here and a few private messages that really steered me right. It's beginning to look like the best bet is going to be an unlicensed (but FCC legal) AM transmitter, the kind that they use for real estate, is going to best fit the bill. It's going to push the range but I believe it will work as long as I can slide it to a frequency not used by any nearby commercial AM station.

 

Now I don't know if a car stereo will be sensitive enough to pick this up or if I'm going to have to throw a cheapo radio in a stage of the cache, but I believe that this is going to work. I'm so confident that I've already placed the final and put a bid on ebay on a transmitter. I hope my `Lincolnshire Poacher' works out well.

I think you will find car stereos plenty sensitive enough to pick up the signal,much better than a cheapo radio.Remember,thats how real estate agencies intended them to work.

One quick word of advise.Buy a transmitter with a quartz lock or "PLL synthisized tuner",They stay on frquency much better than the ones that you just "tune"to the frequency.Small temp changes and other things even indoors will cause the "non-quartz"transmitter to drift off frequency.This can be a real pain if you give the frequency and people try to tune it in and the transmitter has drifted off frequency.Spend the extra few bucks for a quartz locked "PLL" transmitter.

Edited April 3, 2010 by chachi44089

[+Mom-n-Andy]

Cool idea

 

This is the one I used. Transmits a good signal out to about 100'.

 

I don't see a crystal on that board. How well does it do at holding the desired frequency?

[+TheAlabamaRambler]

Low-power AM broadcast radio is what you want.

 

Plenty of examples if you Google "talking house" of how realtors use it.

 

This kit along with a dry-cell battery and solar panel can be built into an ammo can.

 

http://www.ontheair3.com/

 

73 de W4AGA

[+BBWolf+3Pigs]

Cool idea

 

This is the one I used. Transmits a good signal out to about 100'.

 

I don't see a crystal on that board. How well does it do at holding the desired frequency?

 

No problems in two years. The set-up is indoors, and is never futz'ed with.

[+weinema]

Well, the transmitter is currently down (frequence stability sucks)

but heres the link to my FM transmitter cache :-)

 

http://www.geocaching.com/seek/cache_detai...f9-16d3a39c2704

 

It's a small FM transmitter powered by USB port and Windows Media player plays a loop.

 

Happy caching,

Martin

[+chachi44089]

Well, the transmitter is currently down (frequence stability sucks)

but heres the link to my FM transmitter cache :-)

 

http://www.geocaching.com/seek/cache_detai...f9-16d3a39c2704

 

It's a small FM transmitter powered by USB port and Windows Media player plays a loop.

 

Happy caching,

Martin

Thats why I strongly recommend PLL..no frequency drift..great stability..only downside is higher cost..My unit is a Ramsey FM25B from hobbytron.I have been using it almost nonstop for 6 years with no issues.You can build it yourself and save a few bucks!

You can also very the output power to only covor the area you need.If I crank the power up on mine it is about 1/4 of a mile.

Edited April 6, 2010 by chachi44089

[+BBWolf+3Pigs]

 

Thats why I strongly recommend PLL..no frequency drift..great stability..only downside is higher cost..My unit is a Ramsey FM25B from hobbytron.I have been using it almost nonstop for 6 years with no issues.You can build it yourself and save a few bucks!

You can also very the output power to only covor the area you need.If I crank the power up on mine it is about 1/4 of a mile.

 

$140 (sale price) is a lot of money for a cache! The Canakit transmitter I used cost me $20, and I have not have to tweak it since I placed it.

[+Mom-n-Andy]

I still don't have my cache operational but I thought I'd report on what I've learned so far.

 

My first approach was to use a "talking house" AM transmitter found on eBay. At $20 plus shipping, it would have been a good option had it worked. It allows you to record a message and then transmits it continuously. In testing I found that the frequency tended to drift over time. My application requires the broadcast to be heard about 150 ft from the transmitter, and the talking house transmitter would do about 70-80 ft max. There is so much junk, I mean, content on AM radio that I had a lot of trouble finding an empty frequency to broadcast on. But the thing that really doomed this transmitter is that it just wasn't reliable - It would sometimes "forget" the recording or just shut itself off with no warning. I know someone else who has had similar problems with his talking house transmitter.

 

I am currently working with Canakit's Universal FM Transmitter. I bought the assembled kit for $17 since my eyes are getting a little old for soldering, although it would be an easy kit for anyone with any electronics experience to build. (I did have to fix a couple of substandard solder connections though.) For audio input I'm using a discarded 2nd gen iPod that I loaded with an audio file I created in GarageBand. The transmitter works great up to a couple hundred feet with fresh batteries, but as the batteries run down after a couple of days the frequency drifts. I've substituted a 6v ac/dc adapter from Radio Shack for the batteries but am getting a hum/whine (I'm guessing 120Hz) on the transmitted frequency instead of my broadcast. After doing some research, it seems that RF circuits and cheap AC/DC adapters are not a good mix.

 

So that's where things stand at the moment. I found an interesting article (http://www.dxing.info/equipment/wall_warts_bryant.dx) that includes a rectifier/filter circuit, and will build one of those when I get a chance.

 

If anyone has any suggestions they would be most welcome!

 

LOL - by the time I get this working I could probably have bought a nice PLL transmitter for the same cost! I enjoy a challenge though.

[+ihorn]

It sounds like you are creating a very interesting cache. If I were close I would search for it with out a doubt.

[4wheelin_fool]

This thread is pretty cool. It makes me wish that they were still publishing Radio Electronics magazine.

[+GeoGeeBee]

I bought one of these on ebay:

 

http://cgi.ebay.com/1mw-Digital-PLL-stereo...=item3cab24f3c5

 

They have a pretty good reputation among the folks who do the fancy Christmas light displays, and I'm pretty happy with mine. (My "radio" cache will be going online when I get back from my honeymoon around the end of next week.)

 

Please note that this unit has not passed through the FCC type-acceptance procedure and is not labeled as being compliant with FCC Part 15, so it is up to you to make sure that you don't exceed the maximum output or cause interference to licensed stations.

[+Mom-n-Andy]

I bought one of these on ebay:

 

http://cgi.ebay.com/1mw-Digital-PLL-stereo...=item3cab24f3c5

 

They have a pretty good reputation among the folks who do the fancy Christmas light displays, and I'm pretty happy with mine. (My "radio" cache will be going online when I get back from my honeymoon around the end of next week.)

 

Please note that this unit has not passed through the FCC type-acceptance procedure and is not labeled as being compliant with FCC Part 15, so it is up to you to make sure that you don't exceed the maximum output or cause interference to licensed stations.

 

A transmitter with PLL, case, and frequency display for $31? That is unbelievable. I couldn't build one from parts for that. Do you have it in your possession, and does it work?

[+GeoGeeBee]

I bought one of these on ebay:

 

http://cgi.ebay.com/1mw-Digital-PLL-stereo...=item3cab24f3c5

 

They have a pretty good reputation among the folks who do the fancy Christmas light displays, and I'm pretty happy with mine. (My "radio" cache will be going online when I get back from my honeymoon around the end of next week.)

 

Please note that this unit has not passed through the FCC type-acceptance procedure and is not labeled as being compliant with FCC Part 15, so it is up to you to make sure that you don't exceed the maximum output or cause interference to licensed stations.

 

A transmitter with PLL, case, and frequency display for $31? That is unbelievable. I couldn't build one from parts for that. Do you have it in your possession, and does it work?

 

It works fine. If anything, I'm concerned that it might be just a little too much power to comply with FCC part 15. But my house is on a big lot, and I don't think it goes far enough off the lot to cause problems for any of the neighbors.

 

The only problem I had was the audio cable that came with it. It isn't shielded, and I had a horrible 60 cycle hum. A $6 shielded cable from Radio Shack solved that problem.

[+GeoGeeBee]

nekom, are you still working on this?

 

My radio mystery cache was just published a few days ago, you might want to check it out:

http://www.geocaching.com/seek/cache_detai...61-e70e6c9ee65e

 

I was kind of surprised to have two people find it within 24 hours after it was published. It's been pretty quiet since then, though.

[+NYPaddleCacher]

nekom, are you still working on this?

 

My radio mystery cache was just published a few days ago, you might want to check it out:

http://www.geocaching.com/seek/cache_detai...61-e70e6c9ee65e

 

I was kind of surprised to have two people find it within 24 hours after it was published. It's been pretty quiet since then, though.

 

I'm not, but I know how much of a fan of puzzle the FTF on that one is. In fact, just after he found it he sent me email about the "really cool puzzle I got FTF on". I've beta tested a few of his puzzle caches.

[+Coldgears]

nekom, are you still working on this?

 

My radio mystery cache was just published a few days ago, you might want to check it out:

http://www.geocaching.com/seek/cache_detai...61-e70e6c9ee65e

 

I was kind of surprised to have two people find it within 24 hours after it was published. It's been pretty quiet since then, though.

 

Man, it's so disheartening to read about all these awesome caches that are nowhere near me... I wish my local geocaching group still did "cache of the month"...

[+nekom]

I wanted to bump this one more time to see if I'm missing anything here. I have the final hidden, just waiting on some parts to cobble together an AM transmitter that should have enough power while staying within FCC regulations for unlicensed transmission.

 

Here's what you would have to do to find the cache:

1. Decipher a cryptogram.

2. From that, you should know to check the page source where you will find your `one time pad' (you can still use HTML comments for hidden text, right?)

3. From that you should also know to go to the posted coordinates and tune your car's (or other) AM radio to 1000KHz.

4. Wait to hear the repeating message, which are numbers that correspond to your `one time pad', which will reveal the final coordinates.

 

Is there ANYTHING that violates the guidelines or anything else that I should consider changing to make it a better cache? Also would it be a 5 difficulty as a radio is required, or is it safe to assume that EVERYONE'S car will have an AM radio thus making it not really special equipment?

 

Oh and this is actually one of those rare caches which will be placed with permission of the land owner, which is a land trust that buys up hillsides and keeps them from being logged, but opens them to the public for geocaching, hiking, hunting, and whathaveyou. I already have one cache there.

 

Any input is appreciated.

[+GeoGeeBee]

I wasn't sure about the HTML comments, so I added some to my "test cache" page. Yes, you can use HTML comments for hidden text.

 

It sounds like a fun cache... I wish it was closer to me!

 

As for the difficulty rating, I think you could justify calling it a 5. Not because of the "special equipment" but because it will take more than one visit to solve. I rated my similar puzzle a 4.5, but I had my own reason for that... there are several 5/1 caches around here, and not so many 4.5/1, so I was hoping that it would appeal to someone trying to fill a fizzy grid. (My final is in a park, and wheelchair accessible.)

 

I was rather surprised that mine had two finds within 24 hours of being published. But it's not had any since then, and it's been nearly two months. So I wouldn't expect a lot of traffic, unless you have more puzzle fiends there than we do here.