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SlcDX
01-14-2010, 10:32 PM
I have a question, how powerful are those in car ipod transmitters usually?
I have one that says it has a range of 30' around the car, but my tests show about 10' or less.

Tonight in my neighborhood, someone has one on 87.9 (didn't even know they went that low) transmitting what sounds like movie soundtracks.

It is fairly strong but has noticeable interference. I do write these down in my log as they seem to come and go, but I don't think I have the right power down. My best guess is 10 milliwatts.

Russ-PA
01-15-2010, 07:41 AM
That doesn't have to be an iPod re-transmitter. It could be a re-transmitter for satellite TV. Many of us have thought we had some real DX only to find it was a local one of these. Since they're intended to be able to cover a large house, they do get out. Similar units are used with satellite radio receivers in cars, and again a DX'er can be fooled by them. Usually you hear them when you're stopped in traffic. I've noted those with decent coverage as well.

spunker88
01-15-2010, 04:15 PM
I have a cheapo Belkin Tunecast that I have hacked to get more range out of it. This fm transmitter has the antenna hookup labeled on the circuit board, and has a very short wire due to FCC restrictions. I spliced the antenna wire to a pair of VHF bunny ears and I get great range, i would say comparable to a wireless router it covers my whole house easily.

w9wi
01-15-2010, 10:09 PM
I have a cheapo Belkin Tunecast that I have hacked to get more range out of it. This fm transmitter has the antenna hookup labeled on the circuit board, and has a very short wire due to FCC restrictions. I spliced the antenna wire to a pair of VHF bunny ears and I get great range, i would say comparable to a wireless router it covers my whole house easily..

Interesting.

Is the antenna output hooked to the audio input wire? Or is there a separate antenna, entirely within the case? (I expect I'll find out in the morning when I get around to taking the thing apart!)

I bought one to play MP3s in the truck. It was so wimpy that reception was uselessly noisy with the thing sitting on the dashboard less than a foot from the receiving antenna. Bought a 6-foot earphone extension, ran it out the window & back in, wrapping a few turns around the antenna -- that helped, but it still gets clobbered by overload when I drive past the towers...

SlcDX
01-15-2010, 10:33 PM
I have a brand new one (from Xmas) that is a "Monster" brand. I too notice that in certain vehicles the coverage is less than ideal. If the car has an antenna coming out of the hood, it will pick it up fine, but in my Subaru which has a window mounted antenna, it is static no matter what I do. I'd like to open it up and find an antenna wire, but I can't seem to get it open.

Also, Russ, I never thought of it being a satellite audio tx. The volume was noticeably lower than a traditional FM station so I knew I wasn't hearing one, plus the skipping of the songs gave it away too :D

H Hayes PA
01-15-2010, 10:39 PM
I'm noticing the presence of these XM transmitters more and more from cars. I live about 50' from the main drag through town and when I monitor 88.7 for skip it seems every 20 minutes or so I will start getting a signal which slowly fades in, peaks the Sony XDR about 2 or 3 bars then fades away. It fools me from time to time as it sounds very much like an Es opening beginning to poke into FM range. I actually got an ID on one, "XM-161". Who says you can't DX XM?

w9wi
01-16-2010, 12:57 PM
I have a brand new one (from Xmas) that is a "Monster" brand. I too notice that in certain vehicles the coverage is less than ideal. If the car has an antenna coming out of the hood, it will pick it up fine, but in my Subaru which has a window mounted antenna, it is static no matter what I do. I'd like to open it up and find an antenna wire, but I can't seem to get it open.


Well, that was interesting. I just found this page (http://sonic.net/~n7moe/BelkinMod.htm) which is really pretty hard-core. (I definitely DON'T recommend attaching a 120mW amplifier!)

But it does explain what's going on with this thing and how to get it up to an output level where you can use it for its intended purpose.

It seems there are *four* wires in the audio cable going to the plug that's supposed to plug into your MP3 player. Of course, the plug only has three contacts -- common, left audio, and right audio. The fourth wire isn't connected to anything. The seven inches of blue wire within the audio cable are the antenna.

(and because it isn't connected to anything at the plug end, lengthening the audio cable with an earphone extender accomplishes almost nothing. "Almost" nothing, because I suppose there's a bit of coupling between the 7" of blue wire and the wires that do go somewhere.)

Look at the fourth photo on the link, the one captioned Remove second screw and circuit board comes out.. On the left you see the four wires going to the audio plug. The leftmost wire is blue in color, and you can see "ANT" silk-screened on the circuit board. First thing I tried was to tack on about 3 feet of hookup wire in parallel with this blue wire. It accomplished almost nothing.

If you look at the next photo, you see where he tacked on a length of coaxial cable to a blue component labeled "R10". This is actually an inductor, and it's in series with the antenna. It's eating up most of the signal. (it doesn't take much inductance to present a really high impedance at 88MHz) If you look REALLY CLOSE at the photo, you'll note he tacked a very fine wire across this inductor, shorting it out.

I did it a bit differently -- I tacked my 3 feet of hookup wire to the other side of the inductor. (the side closest to the LCD display, the side opposite from the edge of the board)

The hardest part of the mod is putting everything back together when you're done. The wires to the battery compartment are pretty thin and WILL break if you have to manipulate the thing a lot. Luckily they're easy to put back.

Voila! I can now sit the thing on the passenger seat and hear my MP3 player full quieting. I can sit the thing on my desk & hear it full quieting on the HD Radio a few feet away. It's also nearly full quieting on the clock radio about 30 feet away. (but with the big antenna pointed at Kentucky, all I hear on the DX system is WKNK!)

Oh, one of the mod articles says there's a continuous 12mA drain from the batteries even when the unit is turned off. This is probably true. Mine hadn't been used in several months -- but the batteries were completely 100% dead, reading only a few millivolts. Do not expect good battery life, and do take the batteries out if you aren't going to use it for a few days. Mine came with a cigarette lighter adaptor, and I expect to use it.

So if you're wanting to broadcast to the neighborhood, you probably need this guy's 120mW amplifier. But if you're trying to get the Belkin to do what it's advertised to do -- play MP3s through your car radio -- with this simple modification, it'll work...

spunker88
01-16-2010, 08:18 PM
I actually have the Tunecast I, an older model, but the blue antenna wire is also there. I basically spliced onto that blue wire right from the circuit board using insulated wire inside the unit, and then switching to the center wire of a coax cable. I then have an F-plug on the end that i screw onto my bunny ear antenna. I then stand up the antenna and spread the poles about 2' from each other at the top. That seems to do the best for distance.

With the F-plug it is also possible to run the signal a long distance through some coax cable to a radio in another part of the house but I have found that the signal travels far enough without it. Like i said before, for me it provides about the same coverage as a decent wireless router would, the whole house and possibly some outdoors depending on how good the signal is.

I have also built a usb power adapter for it which works perfectly since I am using the computer for the audio source.

SlcDX
01-16-2010, 11:50 PM
I can't find anyone who has modded my particular model (Moster Cable I-carplay Wireless 800) and there is no foreseeable way to get the case open so I guess I'm stuck with a weak unit. Like I said though, it really depends on which car the thing is in.

w9wi
01-19-2010, 10:36 PM
I can't find anyone who has modded my particular model (Moster Cable I-carplay Wireless 800) and there is no foreseeable way to get the case open so I guess I'm stuck with a weak unit. Like I said though, it really depends on which car the thing is in.

On a lot of small electronic devices, there's a screw hidden under a sticker in the battery compartment or somewhere like that.

K3PHL
01-31-2010, 03:58 PM
Those XM and iPod transmitters are very common. 88.3 is an open channel for me and there are at least 3 that use them on that freq and pass on the main road near my house, stop at the traffic light and continue on. The signal fades up, peaks and drops just like an Es event. I even have a very faint one I hear on my APS-9 in a certain direction that listens to XM some distance from me from a fixed location.

I took the liberty of taking my Grundig G8 portable outside to try to find the source one evening. Turns out it was an hour walk to a house 3/4 mile away about 4000-4100 feet according to Google Earth. Now that's a sensitive Sony receiver on the beam! I'm glad I have no close neighbors that use them, otherwise we would need to chat about what frequency he uses.

Russ-PA
01-31-2010, 04:20 PM
I had one of those locally a few years back - I forget what frequency now - where I knew the direction from using the APS9, and I also went looking, although anticipating some distance due to the signal strength, I did it by car. It was a house over a half mile away...

spunker88
02-01-2010, 11:27 AM
I bought one online that goes back to 87.7 FM. I use 87.9, which is pretty much clear everywhere since on 87.7 I get interference from a few Canadian TV 6's that are near me.