As you know from my last blog post the Sstran is on the fritz but that has been added to a list of things to be fixed soon.
Today i added another transmitter to my collection.
As you know from my last blog post the Sstran is on the fritz but that has been added to a list of things to be fixed soon.
Today i added another transmitter to my collection.
Walmart has Scosche FMT4 Fm Transmitters for about $10 bucks.
You might find them in the automotive section around the car stereos.
It’s not much bigger than a pocket sized box of wooden matches.
The FCC ID :RLQAT100
In the package you’ll get the transmitter, instructions and a customer satisfaction survey. Once you get it out of the tough plastic you may feel as though it wasn’t worth the $10 you spent.
It does not include batteries so if you get one of these don’t forget to pick up some AAA batteries too. It takes 2 AAA.
The transmitter is black in color with a silver face around the power button and a super bright blue l.e.d indicating the transmitter is operating.
On the top is a short 5″ stereo plug, on the right side is a frequency range switch to select channels around 87.7 to 88.9 and 106.7 to 107.9 mhz.
On the left side is three toggle switches (like the ones inside the sstran) that allow you to choose the frequency your going to broadcast to.
I chose 106.7 fm, according to Radio-Locator.com this is a clear channel in my area.
After plugging the FMT4 into my computer and selecting some tunes from a shoutcast station i immediately noticed the audio was over driving a small radio i was using to listen on.
I lowered the audio to 50 % and turned off the processing.
It sounded pretty good in stereo and static free at a distance of 1 foot away. Good bass and treble response.
So I turned processing back on and listened again, but this time i walked from one end of the house to the other.
So far so good. The signal stayed right in there without dropping out or static of any kind.
Now for the real test, i drove around the park here which would be a real test of range considering part of the park is in a valley while the rest of it is on higher ground.
Despite some drop outs and several dead places, the FMT4 covered at least 80 to 150 feet but was mostly line of sight.
(roughly 8 homes would have good reception)
I am guessing that part of the antenna is inside the FMT4 while the rest of it is built into the 3.5 mm plug. My home is roughly 4 1/2 feet above ground with aluminum siding and the desk adds maybe 2 feet at the most.
Really this test wasn’t bad considering all the things we have going against us. Maybe tomorrow I will raise the FMT4 up into the air on a pole or something outside and try another range test.
But so far, so good for no more than what it is.
From the manual:
Available Distance 3 Meters
14 Available channels
Powered by 2 AAA batteries
Run Times: In Use 15 hours
Standby : 45 days (1 hour per day)
FCC ID :RLQAT100
Thank You Much!
I think you’ve found something that all Part 15ers can benefit from! A dirt-cheap FM signal, probably VERY adaptable to a STL (Studio-Transmitter-Link) to relay a signal to an AM transmitter. I have to go now, I’m leaving for Walmart!
No range test today
I wanted to raise the antenna up on a 5 foot pole outside on the front porch, but my minivan has different plans for me.
The crazy fuel filter has a cheap plastic ring of some sort and it has worn out to the point that it is leaking gas when i start the van up or sit at a stop light.
So if i did a elevated range test it would have to be after i get the silly fuel filter fix. LOL it’s always something.
But despite the minor set back i was able to tweak around a bit with the sound feeding the FMT-4. I run a gx 280 Dell with processing software and Zararadio. After playing around with the processing , i finally settled on the Orban 8100 preset on Sound Solutions software and some classic rock for music.
It sounded pretty good, lots of bottom end without over-doing it.
Treble and midrange was good too but seemed to be brighter with pre-emphasis on. ( listened to this on a car stereo and then headphones)
The FMT-4 has just enough gain to allow most devices such as i-pods and cd players some head room before overdriving the transmitter.
Without a modulation meter i can’t really tell for sure if it is modulating at 100% but i was able to get a loud signal out of it with a fresh set of energizer AAA’s.
But as I said in my previous post, i like this little transmitter and have already been making plans to place it in a weatherproof case and power it using solar cells and a regulator of some kind.
Most of the plans are in my head, but that’s how ideas become reality.
Carl i hope you and anyone else interested are able to find this transmitter at your local walmart. It is one of the very few inexpensive transmitters that is actually certified and affordable at the same time.
There are some modulators in the electronics section of walmart here but i was not about to pay what they were asking for them and i would hate to give alot for one of those and find it wasnt compliant or could only reach 10 feet. Some were made for ipods and had only a few channels available.
Anyway, good luck and keep rockin’
p.s. now if i could just get that warm tube sound. 🙂
The Scosche Wins!
You’ve done it, rock95seven. The Scosche FMT4 is the neatest thing in recent Part15 history!
Found mine today at Walmart, mounted it on one leg of my indoor 3-leg bamboo radio tower about 7-feet off the floor and checked the carrier with nothing else attached. It was weak.
So I hung 2-feet of clip lead off the audio plugs ring, which is the shield connection, and a solid carrier filled the house. The shield is the antenna.
Ran audio up the tower leg and am now using FMT 4 as an STL (studio-transmitter-link) to drive the AM transmitter in another room.
Outdoors the FM signal is about the same as the AM in coverage.
The audio fidelity is exactly clean and pure.
Thank you for sharing this excellent discovery.
Glad to hear it!
The FMT 4 is truly an amazing find.
Just think, i was about to go out and buy a mr. microphone knock-off from the toy section at Walmart lol. Still might do it just to have something to tinker with.
I have been running a Ramsey fm 25b for the longest time, worried about it not being compliant. The Ramsey is a good TX but I really like to know that if there was ever a question about my station being compliant then I would have to prove it is or isn’t.
Now my Am & Fm both are compliant and I am still using the fm as a STL.
Carl said:
“So I hung 2-feet of clip lead off the audio plugs ring, which is the shield connection, and a solid carrier filled the house. The shield is the antenna.”
I am glad you found that out with the shield because I wasn’t about to crack open the FMT 4, the fact it works is reason enough for me not to peek inside.
However I will try that with mine as well.
Enjoy!
Fastest Project
Putting the Scosche Fmt 4 into service has been the fastest project ever undertaken, since it worked right away (as an STL and FM service). Now I’m worrying about battery cost over time, so the slow part of the project begins: I’m going to install a 3VDC power supply down at the base of my bamboo tower and run DC up a separate leg, away from the audio/antenna wire, and somehow rig it into the Fmt 4.
Regarding the Ramsey FM25, I also had one, and with the variable length antenna, it did cause worry as to whether it was ever set to a legal point. But now, with Fmt 4 being certified, I think the FM25 can be comparison tuned so its performance matches the Fmt 4, and maybe the excuse that a certified unit was used as a yardstick will seem reasonable.
Another thing is, I don’t think frequencies below 88.1 are allowed for Part 15, but since the Fmt 4 does operate on those lower channels and is certified, that seems to be another plus.
Power supply voltage
Great reports on the FMT-4, wish I could find a product photo but no luck on line so far.
Just a quick observation that several of the “2 AA” or “2 AAA” battery powered devices I have include battery eliminator power supplies and those are labeled as having a 4.5 volt output.
I’m guessing this is because the “1.5 volt” rating of a AA battery is a nominal number and that new batteries will test a bit higher than that, along with the notion that the volt rating for many wall warts is without any load.
I just put a DVM on some right-out-of-the-package AAs and it was more like 1.8 volts.
Just some random thoughts on a Friday 🙂
Updates Alerts and Cautions
Thank you scwis for the tip on battery eliminator power supplies.
I just visited http://www.scosche.com and under their “fm transmitters” they do not list the Fmt4, nor did any search find a trace of the product on their site, although they had other items at higher prices. This raises the worry that the item may be discontinued, in which case we might want to rush with last chance panic to get an extra one.
Discontinued
Seems to be the case at my local Walmart. A couple still on the peg, but the reorder tag on the end of the peg had the tell-tale strip of red tape across the tag – do not reorder, discontinued.
and of course I bought the last two 🙂
New Observation on Fmt4
For the first time I selected 87.7 on the car radio, which was near the house in a strong field area, but the audio was distorted and sounded de-tuned. I backed away and once on the street the signal had remained distorted.
However, my C.Crane Plus shows the signal exactly on frequency. All my other radios are dial tuned.
What I believe is that the car tunre is not properly tuned at 87.7, maybe because that’s not an official FM frequency. After being lazy for awhile I’ll find out whether the car tuner has a fine-tuning capability.
Does anyone have a viewpoint about what might be happening?
FCC Info for this unit
Duh! I don’t know why I didn’t think of this before! We have the FCC ID#, and here are the search results. Note photos, schematic and operation page. Nice!
FCC Report on FMT-4, ID #RLQAT100
Interesting Discrepancy
The data referenced by scwis says absolutely nothing about frequencies below 88.1 ! How can that be? Has there been a “fast one” played by the Chinese manufacturer? What does that do to us users who think we have a legit device?
The world is warming while the world is cooling; the seas are rising while they fall; life as we know it is nothing like we thought.
Timewarner cable
My cable tv and internet is provided by TimeWarner.
Several places in town have places directly or close to cable lines that leak the audio portion of the television channels they carry. One known hot spot is the eye doctors i took my kids to several times , two trips out of several our baby fell asleep before we got to the eye doctors.
So i stayed out in the car with the baby and listened around on the am and fm bands. My factory GM car stereo could receive television audio leaking from the cable lines that run in front of the eye doctors.
It sounded slightly off channel on 87.7 but on 87.9 you could not hear it at all. Other places in town yield different results.
Not sure how this helps but in my mind it just means that the radio was not meant to tune that low, it might be a by-product of the IC used in my car stereo .
Despite the fact that the model Walmart sells tunes that low would not keep me from using the FMT 4. It is up to the user to make the right decision to stay off those channels or use them.
I sometimes wonder if the units are sold to certain areas of the U.S. according to where the tv channels are allocated.
In Kentucky, (if i am not mistaken) channels 2, 3 and 6 are over 100 miles away serving Louisville.
So maybe that’s why this area received the models that cover 87.7 & 87.9 mhz? Anyways, I wonder about the antenna on the FMT 4.
The internal pictures provided by the test info provided by the FCC reports were not all that clear. What or where is the antenna?
Is it the small black coil?
More On FMT4
Despite the recent conjecture that the two lower channels of the FMT4 (87.7 & 87.9) might violate the FCC certification, it’s still true that there are 12 “legal” frequencies on board, and the unit does perform like a larger more expensive unit with good audio. I think I’ll do what scwis did and grab the remaining stock at the Walmart. And I have additional thoughts that can probably only be future speculation.
Since analog tv just went off, those frequencies below 88 MHz are now a different world than they were. Does anyone know if new rules apply or are being developed that might change the Part 15 status in that area?
FMT4 Report
I’ve been running one of mine for the last few days and here’s what I saw.
Power – I get about three days continuous use out of the 2 AAAs, phenomenally low current drain. A couple of Ds might easily last over a week, and a couple of those big “dry cell batteries” from grade school science class could probably beat a month. Perfect for solar, and perhaps even solar with a couple of rechargeables and with any sun at all could run 24/7.
Instant station – FMT-4 + Weather Radio
Range – Well, the manufacturer says “3 meters” and the certified unit doesn’t have an antenna. According to the FCC filings, “The output of IC2 has the matching network consisting of L5 and C23 that limit the harmonic content and effect the proper coupling of the antenna to the output stage.” As is, from a third floor window sill, range is about 90 feet line of sight. It’s about 60 feet on the other side of the building, after going through or around 20 feet of building.
Hacking – this part of the schematic shows the RF at pins 10 and 11, with 10 being the RF ground. Since the XMTR has no antenna, I could probably get a magnifying glass and get a lead on the RF out at L5. However, a short lead attached to the ground side would also form half an antenna. If you remember the Tiger Tail sold in PopComm magazine, that’s an example.
FCC note – this trick would void certification but the range isn’t exceeding what you would expect from a compliant unit. It is also reversible, in that I can remove the wire 🙂
More hacking – It will be fun to take one of these and put a bit more voltage to the system, it likely has an internal regulator and more voltage doesn’t mean more range unless it’s a spark gap transmitter. However, as this unit was designed to be battery powered it is possible the unit is more geared to work OK with not very much juice. It would be interesting to see what making 4, 5, or 6 volts available might do. Adding the other side of the antenna will be interesting, too.
Lot’s of experimental fun for $10.00
Ideal
Scwis, I appreciate your lab report on FMT4. You have shown the real reason I detected an “antenna effect” from the shield. It turns out that was 1/2 of an antenna. I now have three of these units and keep thinking about one more hanging on the hook back at the store.
Your findings on higher voltage and your hacking of a true antenna will be enjoyed.
On that idea of solar power, I seriously want to solar power an outdoor antenna site, and ask now if anyone can specify an appropriate small panel and source of supply (?)
It’s Been Modified
To scwis and all:
The diagrams in the FCC Exhibit are not the same as the transmitter here on the bench. First, the circuit-board photo is nothing like what I found by opening an Fmt4.
On this one the cable shield attaches to a spot on the card marked “ANT.”
What makes it more complex to “reverse-engineer” is a total change in the IC. The FCC schematic shows a single 22-pin IC, but my unit has two smaller flat IC chips, one with 7-pins, and a much tinier flat IC with 16-pins.
The sundry parts, resistors and capacitors, are so ultra-tiny they may be beyond identifying.
Scwis! Rescue the situation!
Any numbers on the IC bodies? Range!
That way we could get the datasheet and read the chip purpose and and get a pinout.
Changed to a clearer frequency (88.9) and adjusted the wire scrap to be 1/4 wavelength (~33″)
Oops! Don’t do that – range went way over the limit – around 500 feet (1000′ diameter circle), tuned with an EOM Pioneer FM receiver in a Toyota with a winshield antenna. And the content was intelligible (but not pleasant!) for another 300′
A half wave dipole (33″ wire on the RF out side as well) could probably approach 1/4 mile if it was elevated a bit, so I’ll probably not do that.
Not bad for $10.00!
Random thoughts on solar power
If my unit used a set of batteries in 3 days (or 72 hours), and
If a AAA battery has a capacity of about 1000 milliamp hours, and
If the batteries are in series the current drains twice as fast so the voltage can double,
Then the unit uses 1000mAh/72h, the “h”s cancel, and
unit used 13.88 mA for each hour of operation by this calculation, say 14mA/h to make it easier.
So, I want a system that can deliver 14 mA per hour and can store enough current to power the unit when there is no sun. I’m in the Pacific Northwest, so I’d plan 19 hours of darkness capacity 🙂
14 mA per hour X 19 hours = about 270 mAh of storage. A rechargeable NiCad AAA size battery is about 1.2 Volts and 300 mAh, so a battery pack of 3 in series would deliver 3.6 volts (which is what two brand new AAAs deliver at 1.8V each)
So, what output solar cell?
If the battery pack should hold 270 mAh, and
If the sun is only available 5 hours a day,
Then the panel needs to deliver (270/5)+14mA per hour in sunlight
So a perhaps 3.6 volt, 100 mA/h panel
This is pretty simple stuff, so I might go forward without a charge controller – just see if the batteries can take it. An example of what looks like a fairly inexpensive and simple low power controller, available for around $10.00 at digikey, is here:
http://pdfserv.maxim-ic.com/en/ds/1666.pdf
IC Description
The larger IC, 14-pin, has a remarkably “barely visible” marking
BArdW
BW007F
The marking is kind of a purple-red against black, and I suspect might be designed for a special colored light to view clearly. It appears that the crystal is connected to pins 5 & 6 of this IC.
The smaller IC, 16-pin, has a plain black matt finish, but there might be an even more invisible marking, which my lighting does not expose.
If I observe something more I’ll log back on.
Test Results
As I previously reported, the version of Fmt4 on our bench is different from the pictures at the FCC certification site. The shield of the 6″ audio cable is attached on the circuit-card at a point marked “ANT.”
Just to guess at what the designer intended: since the Fmt4 is intended for use with a personal audio device like an Ipod, it does not take into account the much more elaborate grounding system that would follow the shield into the Fmt4 in a full computer/audio system. In its designed use, the Antenna output serves as shield ground input, which seems plausible if the impedance of the final stage is low. The 6-inches of audio cable shield and the few extra inches of “ground” wiring inside the Ipod would provide a modest antenna length.
So here’s what I did. I unsoldered the shield from the ANT connection and connected it to Fmt4 GND, the same as the battery “B-minus.” Then, using the length mentioned by Scwis, I added a 33″ wire to the ANT connection and ran it out a space in the battery compartment with the lid removed.
At 88.5 MHz the signal blankets the yard, 200′ by 60′, with the transmitter indoors run up one leg of a 3-leg bamboo tower. The power level indicator on the C.Crane Plus radio went high and low while moving around, but the audio remained solid all the while.
Later today I’ll drive the car radio and see what happens.
By Car
Oh my goodness. Based on the setup described in my previous post on this thread, I’ve gone by car to test 88.5 MHz coverage, and it’s at least twice or better than my best AM coverage. It’s probably too much, as Scwis reported in the corresponding test he did. I’m guessing that it goes 300′ FROM INSIDE A BRICK HOUSE!
It was rock95seven who found the Scosche, and what a great find it is!.
Small Footnote
This is a relatively small footnote after the amazing results from the Scosche Fmt4. But here’s the deal.
When the battery’s are fresh, the LED glows blue. Then, after some time, the color switches to green. Eventually the LED dies and emits no more light, BUT, the FM carrier is still there and keeps going!
ICs in FMT-4 seem to have non-standard part numbers
So no obvious data sheets come up in searches. However, that’s probably not a huge setback as both Carl and I have discovered it is possible to exceed what would be expected to be permissible range with just a few simple tweaks.
It also would seem important to do some RF isolation on any external power leads as anything connected to the transmitter seems to extend range. I might look at using an iron powder toroid on the DC power leads to stop that.
Seems to be an incredibly affordable way to add an FM side to my NOAA Weather Radio AM outlet.
Proposal for Complying with Certification
A consensus was reached in this thread that with a 1/4-wavelength antenna the Fmt4 seems to exceed the expected (legal) range.
Therefore I pictured in my mind what conditions would be true if the Fmt4 were operated according to its intended application, namely plugged into an Ipod.
We know that the audio cable with shield connected to ANT is 6″ from the Fmt4, and I am guessing that an Ipod is approximately 5″ in length, and would serve as a additional antenna, totaling 11″. This, then, is probably the antenna length needed to meet certification.
I was reminded of something by this requirement to throttle power in a lesser direction, and went outside to see my speedometer, which shows a maximum of 140-mph! That’s about twice what’s normally reached on the interstate!
But First
On the way toward the technique for complying with certification described in my last posting, I tinkered with wavelength formulas and thought of trying 1/8-wavelength instead of the previous 1/4-wavelength. Also, I lowered the Fmt4 to the mid-point on my indoor tower, instead of up high. It’s now mounted at 4′ instead of 7′
The difference is noticeable around the yard where the uphill path slowly grows dimmer whereas the downhill path remains fairly strong.
At 88.5 MHz I have 17.375″ of antenna.
Driving test coming later.
1/8 Wave Antenna
As promised on my last post I drove the car and monitored 88.5 to see how well the 1/8-wave antenna reaches out, and it is truly 1/2 of the previous test with a 1/4-wave antenna.
The 1/4-wave antenna doubled the range of my best AM at 1680, which was 150 to 200-feet doubled, for an FM distance of about 400-feet.
The 1/8-wave antenna on the Scosche Fmt4 is exactly half that in length and reach.
Now we’ll sit back and wait for scwis to try higher voltages.
Temptations of a Part 15er
Then, after finding that an 8th-wave antenna on the Fmt4 reduces the transmission distance by half compared to a 4th-wave antenna, I got to wondering: does that mean that a half-wave antenna will double the longer range to 800-feet?
These thoughts have got to stop. Does this site have a counselor for out of bounds Part 15 risk takers?
And the Scosche Fmt4 is so tiny.
Half wave antenna
Carl postulated:
…does that mean that a half-wave antenna will double the longer range …
This is not easy to predict since the output impedance requirements of this transmitter are not known. There is a difference in the radiated patterns of the antennas you mention, but I suspect the dominant factor in determining the range with this unit is the match between the transmitter and the antenna which you will best find by experimentation. A 1/4 wave antenna has a low resistive impedance and a 1/2 wave end fed will have a high resistive impedance so it will depend on which the transmitter is best suited to drive.
Neil
Horizontal and Vertical
Most full power FM stations have antennas that radiate both horizontally and vertically, and a few stations apparently have two separate transmitter/antenna sets for the two planes. Case in point: WSIE Edwardsville, IL 50 kw horizontal, 41 kw vertical (radio-locator.com).
Meanwhile, just about every Part 15 discussion describes a vertical antenna. Is it so hard to achieve horizontal/vertical polarization with just three turns of the antenna?
1/3 of the antenna would be vertical, 1/3 of the antenna would form an L onto the horizontal plane pointing north, and the remaining third would make a right angle onto the same horizontal plane pointing east. Coat hanger wire or other hardened wire would do the trick.
Other Scosche Thoughts
Here at Part 15 College the student is back with hand raised.
PREVIOUSLY we have discussed shortening the antenna as the way of controlling the field strength (range) of the Fmt4. However, in FM it is also true that lowering the antenna closer to the ground is another method of reducing the effective range.
Somewhere in the threads it’s been said that an FCC document gives the ballpark figure of “200-feet” as the expected range of a legally compliant FM intentional radiator under Part 15. My question asks, does that mean 200′ from transmitter (point A) to a straight line point 200′ away (point B)? Or, does it mean 200′ feet from (point A) outer boundary, to (point B) the transmitter, to (point C) the other outer boundary?
Addendum
Radio-Locator.com is great. They report 87.7 MHz is not a valid frequency in the U.S. Well, we knew that.
But, they show two stations have been assigned at 87.9 MHz. That goes against what we thought we knew.
KSFH in Mountain View CA has 10 watts, and K200AA in Sun Valley, NV, is 28 watts translator for KAWZ, a 100 kw religious station in Twin Falls, Idaho.
Obviously this is pertinent since the Fmt4 offers 87.9 as a choice.
If you’re looking for a valid FCC license, and since there are no more Channel 6 analogs, 87.9 might be a smart shoe in the door!
Re-powering the Scosche Fmt-4
As noted in the earlier report, one of the next hacks was to put more than the dribble of DC power into the unit. In this case, by replacing the AAA batteries with a more robust power source.
Hooking up to an inexpensive, low voltage variable supply didn’t really get the job done because the unit I had wasn’t filtered very well. Ended up using a wall wart from a broken LG cell phone offering 4.5 volts at 900 mA. That unit was well filtered and quiet on the Scosche.
Anything above around 3.8 volts has the on-board regulator working too hard. The regulator starts throwing off so much spurious crud that it swamped the nearby NOAA receiver.
My solution was to double the 15 mA current allowance to 30 mA and use Ohms law to calculate the value of a voltage limiting resistor. Turned out a 47 Ohm, 1/4 watt carbon resistor from the junk box worked perfectly.
With the resistor in place the voltage is held back to a bearable level for the voltage regulator in the Scosche and the little bit of additional current available gives the transmitter all the oomph it might need to pull out of the power supply.
From that I would guess that three rechargable AAA or larger cells @1.2 Volts each would be perfect.
Because anything connected to the Scosche becomes part antenna, I wrapped the DC leads through a toriod from an old PC Part 15 compliance filter several times as an ad-hoc RF choke.
With a 30″ piece of wire attached to the negative terminal of the battery case it’s gets out as far as I feel comfortable going 🙂
For a bit of discomfort, I tried a 5/8ths wave
Just for fun, I tried a 5/8ths wave length on the wire I attached to the negative terminal oin the battery compartment, to see if there was any difference in range.
I used a 5/8ths calculator I found here:
http://www.qsl.net/w4sat/five8th.htm
I’m on 88.9 so my extended wire is around six and a half feet.
The result was quite surprising. The range did not increase, in fact in some directions the range was less, but the signal quality was much better. AS I understand it, the 5/8s wave length flattens the envelope a bit so hopefully I am directing the signal to more constructive directions.
Excellent SCWIS
Thank you scwis for sharing the results. Luckily I checked back to this thread, which I thought had been abandoned. The Scosche really made a splash on the part 15 site. I am a true believer in the unit.
Busy busy busy
Too busy actually.
Just to let you know I haven’t let this thread or my experiments with the FMT 4 fall to the wayside.
My wife and I are actually getting things ready around the house for a move to the lower end of the park here. A bigger place should be opening up by August and we grabbed it up as soon as we heard about it.
There are only two double-wides here in the park and our big family needs the room. Only thing i dread out of all this (besides moving lol) is i am wondering how my little stations coverage is going to be after we make this move. It’s pretty much a hole down there and i feel as though i could lose some coverage to the upper section of the park and fringe coverage.
EDIT: I really am enjoying the FMT 4.
Only trouble I have is the battery life of these aaa batteries is pitiful.
Ok so yeah they are rechargeable and I shouldnt expect more than 2 – 3 days continous operation on these little batteries, but i am getting tired of changing the batteries out.
Another power source to consider is USB , eliminating the need for batteries and coupled with a choke inline somewhere on the usb cable you could adjust for range by measuring out the length of usb cable and insert your choke according to your needs.
That should kill two birds with one stone,
1) power source
2) increase range.
USB ports offer 5v, if your worried about too much voltage you could add a resistor inline with the Hot Side of the usb cable.
The choke should keep the rf from entering your computer.
I suggest using a ferrite core. Any thoughts?
End of EDIT.
When i get a chance i’ll post more details for the following:
http://www.part15.us/node/2017 Going Green
http://www.part15.us/node/2029
Probably best to pull down the USB Voltage
When I powered my Scosche with a 4.5 volt cell phone charger the voltage regulator in the Scosche was putting out quite a bit of hash. An inline resistor will fix it right up.
FMT4R
I bought one of these today in Walmart for $12, after reading about it here. It was the last one on display. It’s pretty good and I think overall the sound has better quality than my Tunecast II. First experiments with some simple wire antennas in a room gave me about 50-100 feet, and full coverage around my building. I’ll do some more to it, and maybe have a look inside to see how it might be modded. I’m looking now at the circuit diagram to get an idea of what’s going on. Distance is no better than the (modded) Tunecast II. I’ll set it up on my first floor patio tomorrow night and see how far I can get a signal out. That’s a pretty good place to try it since either way left or right is a very long car park, without obstructions. Overall a pretty decent stereo broadcast and handled my OTR very well to the craftroom at the back of the place. If my ears are not playing tricks on me, the quality of the music improved when I used a standard Radio Shack lead to extend the small cable from laptop. I already want another one to open up and rehouse with a better power source, integral antenna and case. So I’ll have to get in the car and drive around a couple of Walmarts. For performance this reminds me alot of a CanaKit I built some time back, but the price makes this a must have. This is the basis for a very interesting project. What was written here by others is all true. Get one!
Final word from me on the FMT4R
By itself it is pretty accurate that it will give about 3 meters. With an antenna the distance was vastly improved. This output could be improved upon and still be legal! Perhaps by examining the attenuation of the device, it might be easily improved. I tried a 9v battery on it. There was little difference, perhaps 25-50% improvement in distance, but nothing too remarkable, and hardly worth the bother. A small piece of wire gave me a solid 50 feet. Forgetting all manner of theory and simply stringing a simple long wire antenna up across my patio gave me about 75-100 feet, with the occasional drop out after that and picking up the signal again. I used a simple hand held radio with small antenna, which is really not the best for these things – it hardly registers my Tunecast (in comparison). I’ve found that with a better radio I can usually double what I get on that. My view is that if it is rehoused to provide robustness and desktop usefulness, with a simple antenna (probably telescopic for cuteness and nothing else – a piece of wire would suffice) and a steady power source this is a good house-hold transmitter for my OTR and online radio stations which definitely outperforms some things I’ve even bought or built – but without the fuss. Performance overall seems dependent on the antenna only. The stereo reproduction is pretty good. The FCC won’t bother you for using this thing. I’d like to know what it is putting out. I’m thinking that like the Tunecast if you short a resistor or two and this might give you a good 200 meters. I’m wondering what it would be like on a whip or a legal FCC antenna. Trial and error and brute force and ignorance is sometimes surprising. 🙂
Continuous operation for 45 days
Been running the unit continuously since the middle of June.
Eventual plan would be to use it for STL to an AM transmitter, more later.
FMT-4 Back at WalMart
Restocked under a slightly different SKU and package design, there was an entire new Scosche display for the Holidays with the FMT-4, a ground loop eliminator (which I bought) and an additional transmitter model (which I also bought)
I noticed much the same thing
I noticed much the same in a local Wal-mart, not the one most closest to me (where I bought my first one), but one nearby which had a three or four of them hanging, when just recently they’d had none. I suspect they are quite good sellers, since they are the only things like it on the auto display, the only obvious alternative was the typical car lighter thing.
On the hunt for cheap stuff though, I was in a $1.09 store the other day, not sure if you have those near you or in your state, but I was amazed to find two different little transmitters for games machines (I don’t know the machines, probably intended for the Sony PSP). One even came with a set of receiver headphones! The only obvious drawback is that the transmitters are powered off the games machines and both also drew their audio from the slot-in board connections, so should be pretty obvious about what is coming from where. So altogether pretty useless in themselves but inside likely interesting and TINY little circuits. I passed these up last week, but thinking now that they could lead to some interesting projects. The store is a little far but I might get back over there next week and take another look at them. I’ll also check the $1.09 store close to here just in case he has the same things.
I’m not 100% sure, but think of them looked like this: http://www.youtube.com/watch?v=zTsRoTGKgPs
Walmart now selling the FMT4RA
I bought two so I could tear one apart. I discovered that the “ant” tab is either the + or – to the two leads on the stereo 3.5mm plug. Two leads off the “ant” connection. I guessed it ended up being a sort of half-folded dipole. The lead is 7″ so I chose 107.7 mhz (107.7 1/8th wavelength = 13.75″).
Then I connected a 14″ piece of wire to the negative battery terminal.
I set an mp3 player on a fencepost with everything else dangling below. Something like this, antenna-wise
–mp3 player
….||….
….||….
….||….
….||….
–FMT4RA
….|….
….|….
….|….
….|….
….|….
….|….
….|….
….|….
Then I drove off, listening to the truck radio. I got over a quarter-mile before I noted ANY loss of signal, just from the sound of the radio… and even then it was just noticeable. That’s right. It was 1396 feet. Not kidding. Not lying. Used a hand-held GPS and that matched the truck odometer. Amazing. Went back to Walmart and bought them out (two more units). Then called my kid at college to have him clean his local Walmart out.
I think there’s some things that allowed this sort of performance.
1. I live in the mountains, very rural, and 107.7 is fully clear. Also, I’m not real worried about the FCC out here with regard to Part 15 unless the antelope start listening to radio.
2. I chose a frequency that matched my guess of the antenna configuration.
3. The vertical dipole configuration matched the antenna on the truck. I think this makes a big difference with short range, low-power radio transmission. I didn’t try the dipole horizontally, but my guess is that it would cut the range way way down. I’ll try that, as well as a yagi jig I’m building to explore just how far I can get out with this little thing.
Because it’s a blast.