Xm Ideas

[bmwsoldat]

HALLO ALL!!!

i have an '05 ST. Was wondering who has any ideas about mounting xm/siris radios. plus their antenna.
tanks!

[Xaque]

I'm currently looking into the same thing...

...may I suggest CycleGadgets.com (http://www.cyclegadgets.com/Products/?cat=SATRAD)

They sell many different mounting options.

-Xaque-

[BubbaZanetti]

my only suggestion is, don't listen to what people say about not cutting the antenna wire. if you're careful, you can easily shorten the wire and save some dough. my pet rabbit chewed through the one in my house in 3 places and i repaired it just fine. never got around to putting it on the bike this year, the output from the receiver was quite low and i don't have an autocom or anything to boost the signal

[wmubrown]

my only suggestion is, don't listen to what people say about not cutting the antenna wire. if you're careful, you can easily shorten the wire and save some dough. my pet rabbit chewed through the one in my house in 3 places and i repaired it just fine. never got around to putting it on the bike this year, the output from the receiver was quite low and i don't have an autocom or anything to boost the signal
I've shorted the cable for a couple people... yes, it's doable. You WILL lose some signal strength, however, so beware. The cable is made the length it is for fine tuning to the receiver, changing the length changes the sensitivity.

[dronning]

Have you got an XM yet? Do you have want a GPS?

I'd look into the new Garmin Zumo (http://www.garmin.com/zumo/) due out this month.

Dave

[rdsmith3]

I have an XM Roady 2 with a Hoon Hardware holder. I use Etymotic er6i ear phones and a Radio Shack in line volume control. This set up has been very durable and works really well.


http://r1150r.smugmug.com/photos/64633255-M.jpg

[BubbaZanetti]

I've shorted the cable for a couple people... yes, it's doable. You WILL lose some signal strength, however, so beware. The cable is made the length it is for fine tuning to the receiver, changing the length changes the sensitivity.



i've heard this before and it sounds like hooey to me. how can a double shielded length of coax cable act as a signal strengh booster for a very short wavelength signal sent out by a satellite? i've always been curious about this statement.

[dickhein]

Ditto to what rdsmith3 said.

[alien_hitchhiker]

If you prefer helmet speakers consider a Boostaroo (Radio Shack also markets one with their label) combined with an inline volume control.

I tried using a radio as an amp but kept having electrical noise problems. The Boostaroo is clean.

When I feel like music - which is only on looong rides - I stuff in some earplugs and crank it up. The ear plugs filter out the road noise and I wind up with reasonable sound quality.

[BradfordBenn]

i've heard this before and it sounds like hooey to me. how can a double shielded length of coax cable act as a signal strengh booster for a very short wavelength signal sent out by a satellite? i've always been curious about this statement.

It is actually that the wire is tuned to the proper length to prevent the skin effect or "bounce back" of a signal which is how the signal is lost. I do not understand it fully but understand it enough to know that the goal is to have the cable length be 1/4, 1/2, full, two, four... etc wavelength. The goal being that the cable termination comes at a good point in the wavelength so that bounce back does not come back as interference.

[HexST]

one method
http://Knick.smugmug.com/photos/74002721-M.jpg
another
http://Knick.smugmug.com/photos/95358146-M.jpg

[wmubrown]

i've heard this before and it sounds like hooey to me. how can a double shielded length of coax cable act as a signal strengh booster for a very short wavelength signal sent out by a satellite? i've always been curious about this statement.
The cable is not acting as a 'booster' as you put it. An antennae and receiver are 'tuned' together for best signal reception and is a complicated set of math involving the capacitance, inductance and resistance in the system between the antennae itself, the cable to conduct the signal, and finally the receiver. If you alter any bit of that, you will decrease the signal strength. Part of that equation is the length of the cable. Wire has resistance, the amount can be calculated and is specified in ohms per foot. The engineers who designed the system know this and specify the proper length for maximum signal to the receiver. If you shorten this cable, you reduce the resistance in the system, altering that very fundamental characteristic and the signal will degrade. Also important, as BradfordBenn pointed out, is the multiple by which you reduce the cable length. An antennae signal is an AC signal. Picture a 60hz waveform traveling down a wire. A perfect signal is one in which the waveform starts AND ends at a zero crossing (preferably at the same phase, and not 180 degrees out), reducing reflection from the terminating point back up the cable (and thus creating noise, further degrading your signal). So reducing the cable length not only weakens the signal, but also can cause reflections back up and down the cable if the proper ratio is not preserved when shortening it (1/4, 1/2, etc).

Or to put it more simply... WHY would XM waste money on expensive cable by putting 28' on an antennae lead if a 6" lead would work? Ever price that small diameter coaxial cable?? It's expensive stuff.

[andy45320]

I'm currently looking into the same thing...

...may I suggest CycleGadgets.com (http://www.cyclegadgets.com/Products/?cat=SATRAD)

They sell many different mounting options.

-Xaque-
Try this place...they have some cheaper parts than most places...ordered everything I need (including the harder to find extra c-clamp for my roady2) Also bought two 4' xm antennas...will let you know if they work better or worse.

Helps if you add the link - http://www.myradiostore.us/

[BubbaZanetti]

The cable is not acting as a 'booster' as you put it. An antennae and receiver are 'tuned' together for best signal reception and is a complicated set of math involving the capacitance, inductance and resistance in the system between the antennae itself, the cable to conduct the signal, and finally the receiver. If you alter any bit of that, you will decrease the signal strength. Part of that equation is the length of the cable. Wire has resistance, the amount can be calculated and is specified in ohms per foot. The engineers who designed the system know this and specify the proper length for maximum signal to the receiver. If you shorten this cable, you reduce the resistance in the system, altering that very fundamental characteristic and the signal will degrade. Also important, as BradfordBenn pointed out, is the multiple by which you reduce the cable length. An antennae signal is an AC signal. Picture a 60hz waveform traveling down a wire. A perfect signal is one in which the waveform starts AND ends at a zero crossing (preferably at the same phase, and not 180 degrees out), reducing reflection from the terminating point back up the cable (and thus creating noise, further degrading your signal). So reducing the cable length not only weakens the signal, but also can cause reflections back up and down the cable if the proper ratio is not preserved when shortening it (1/4, 1/2, etc).

Or to put it more simply... WHY would XM waste money on expensive cable by putting 28' on an antennae lead if a 6" lead would work? Ever price that small diameter coaxial cable?? It's expensive stuff.


thank you, just the answer i was looking for, makes very good sense to me now!

[andy45320]

I have an XM Roady 2 with a Hoon Hardware holder. I use Etymotic er6i ear phones and a Radio Shack in line volume control. This set up has been very durable and works really well.


http://r1150r.smugmug.com/photos/64633255-M.jpg
I have the exact same setup on my 04 GT and soon to be on my new to me concours :thumb:

[hlothery]

The cable is not acting as a 'booster' as you put it. An antennae and receiver are 'tuned' together for best signal reception and is a complicated set of math involving the capacitance, inductance and resistance in the system between the antennae itself, the cable to conduct the signal, and finally the receiver. If you alter any bit of that, you will decrease the signal strength. Part of that equation is the length of the cable. Wire has resistance, the amount can be calculated and is specified in ohms per foot. The engineers who designed the system know this and specify the proper length for maximum signal to the receiver. If you shorten this cable, you reduce the resistance in the system, altering that very fundamental characteristic and the signal will degrade. Also important, as BradfordBenn pointed out, is the multiple by which you reduce the cable length. An antennae signal is an AC signal. Picture a 60hz waveform traveling down a wire. A perfect signal is one in which the waveform starts AND ends at a zero crossing (preferably at the same phase, and not 180 degrees out), reducing reflection from the terminating point back up the cable (and thus creating noise, further degrading your signal). So reducing the cable length not only weakens the signal, but also can cause reflections back up and down the cable if the proper ratio is not preserved when shortening it (1/4, 1/2, etc).

Or to put it more simply... WHY would XM waste money on expensive cable by putting 28' on an antennae lead if a 6" lead would work? Ever price that small diameter coaxial cable?? It's expensive stuff.



WOW.......I'm dizzy! :D

[bmwsoldat]

HEY!
You guys did fantastic! i got some good ideas, i have three xm radios.
TAO,ROADY2, and a SPORTSCASTER.
the roady and the sportscaster are really small, light wieght and i will more then likely mount them in a more permant place.
the roady has decent sound output.
the sportcaster too.
the tao is too low.so they only good thing about it is that i can take off the bike and walk around. neat feature.

to the rabbit:
my cat has a tendency to eat/chew wires. i hope although i like her allto that she woud get shocked just once! :clap
my dad taught me a valuable lesson about light sockets and metal objects going in them. NEVER DID IT AGAIN!
BTW:
seems common sense about the wire. they all seem to be the same lenght.i understand that companies want to make money not waste it on thier products by wasting resources. penny pinchers!

oh,i do like that new garmin, zumo550!
i use an axium for gps/mp3 duties AND with large memory card watch crunched dvd's on it.
thanks again!

[bmwmick]

Or to put it more simply... WHY would XM waste money on expensive cable by putting 28' on an antennae lead if a 6" lead would work? Ever price that small diameter coaxial cable?? It's expensive stuff.

John,
They only make it that long so you can position the antenna outside the vehicle on a horizontal surface. I have shortened several of these antenna assemblies and tested signal strength both before and after. There is no difference in signal strength.
The only time you need to worry about feed-line length is if you are transmitting. We are not.

[BradfordBenn]

I will back John on this one, and his answer is better then mine. I talked to the engineers for the XM product we have at work today about this issue. John has it right on the money. They had looked at shortening it, and the attenuation due to noise was not worth the cost trade off.

[bmwmick]

I will back John on this one, and his answer is better then mine. I talked to the engineers for the XM product we have at work today about this issue. John has it right on the money. They had looked at shortening it, and the attenuation due to noise was not worth the cost trade off.


Attenuation due to what noise? Like I said, no difference in signal strength. Since it is a digital signal, no noise gets through. This isn't an AM radio here.

[BradfordBenn]

Attenuation due to what noise? Like I said, no difference in signal strength. Since it is a digital signal, no noise gets through. This isn't an AM radio here.

The digital signal is transmitted via an analog carrier wave. So if there is noise on the signal the bit stream gets corrupted, think about slow internet connections. The audio will drop out and the receiver has to do more buffering. Also the digital ons have to be higher then the noise and less rounding of the wave form. Kind of like a scratched CD.

[cjack]

Interesting discussion. There doesn't seem to be any valid reason for not shortening the coax that I have read here. If say a 75 ohm antenna feeds a 75 ohm coax, and the receiver input is 75 ohms, then there are no reflections of the signal transmitted down the coax, no standing waves, and no additional loss in the coax. The only result of having a longer coax is the inherent loss in the coax to the signal due to a longer coax run.
I also see some reference to using multiple half wavelengths of coax. While that would result in the receiver seeing the antenna impedance just as if the antenna were connected to the receiver without a coax length, regardless of a mismatch, that is of no consequence here if there is a match as stated above.
If there is a valid reason not to change the length of the line, I haven't seen it mentioned here. It would involve some discussion of an antenna which is not matched to the coax characteristic impedance and where the length of the line is selected to present a favorable impedance to the receiver input (to make it tuneable, perhaps) or in the case of a multiple half wavelength of line, to present the antenna impedance to the receiver input regardless of the characteristic impedance of the coax.
Longer lines have more loss than shorter ones, matched, and even more loss mismatched. Again if there is some required length, the reasons are not evident.
On the noise discussion, I'm not seeing how a longer line can result in a better signal to noise ratio, unless the noise is a much higher frequency than the signal and therefore the noise would be attenuated much more than the signal for a given coax length since the losses in the coax increase with frequency.

[BubbaZanetti]

I
If there is a valid reason not to change the length of the line, I haven't seen it mentioned here.

Again if there is some required length, the reasons are not evident.




i think it's mainly just to get rid of the extra 95 percent of the wire you don't need. with respect to handlebar mounting, etc, the wire can really get in the way if your receiver and antenna are only a few inches apart. i was originally going to mount the receiver across the top of the tripple tree on my S and the antenna on the top of the clutch reservoir.

[Furman]

Don't these small antennas have a preamp built in so the signal is stronger when it reaches the receiver? And I think the lenght of the coax is due to the design of the antenna to be mounted on a car roof, many feet away from the receiver. The shorter the cable the less signal loss is what I have found when I make contact with amateur radio satallites (Ham Radio).

I use a Sirius receiver on my K bike with a MixIt module for my other radio and GPS. The antenna for the Sirius is mounted on a tab behind the rack on the rear of the bike.

[wmubrown]

John,
They only make it that long so you can position the antenna outside the vehicle on a horizontal surface. I have shortened several of these antenna assemblies and tested signal strength both before and after. There is no difference in signal strength.
The only time you need to worry about feed-line length is if you are transmitting. We are not.
True... they set the length of the cable for installation in cars, but that length was taken into account in the design for the best reception. You can definitely shorten the length of the cable, signal lost won't stop the radio from working. I've done it for a couple people, but you do lose some signal strength - the XM receivers showed a 1 bar drop. I'm not sure what you are using to measure signal, and there are a lot of factors involved in signal strength. I don't have a signal strength meter to get accurate measures. The discussion on impedance is explained better here http://en.wikipedia.org/wiki/Antenna_(electronics), excerpt:

Impedance
"Impedance" is analogous to refractive index in optics. As the electric wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance. At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

[wmubrown]

Attenuation due to what noise? Like I said, no difference in signal strength. Since it is a digital signal, no noise gets through. This isn't an AM radio here.
The noise is the signal reflecting back up the wire from the receiver. The digital signal is carried on an analog wave.

[bmwmick]

I'm not sure what you are using to measure signal, and there are a lot of factors involved in signal strength. I don't have a signal strength meter to get accurate measures.

John,
There is a pretty good signal strength indicator built-in to just about every roady/skifi radio receiver. I used the BER% test to determine if cutting the coax to 6" made any difference in reception quality or signal strength....it made no difference. :)

Here are some fun diagnostics if you are curious:
http://www.xm411.com/phpbb/viewtopic.php?t=2073 (Diags)
(I use the 2 3 2 mode to power up my Roady with NO LED backlight a lot on my bikes)
http://www.xm411.com/phpbb/viewtopic.php?t=172 (2-0-7 details of BER%)
http://www.xm411.com/phpbb/viewtopic.php?t=4092 (cable splicing instructions)

BTW: The little magnetic 'chicklet' antennas that my Roady2 uses appear to be 1/4 Wavelengh horizontally polarized antennas. A full wavelength at this frequency (2.3Ghz) is just under 5". The "Home Kit" antenna appears to be a 5/8 Wavelength antenna (about 3") :brow

[wmubrown]

John,
There is a pretty good signal strength indicator built-in to just about every roady/skifi radio receiver. I used the BER% test to determine if cutting the coax to 6" made any difference in reception quality or signal strength....it made no difference. :)

Here are some fun diagnostics if you are curious:
http://www.xm411.com/phpbb/viewtopic.php?t=2073 (Diags)
(I use the 2 3 2 mode to power up my Roady with NO LED backlight a lot on my bikes)
http://www.xm411.com/phpbb/viewtopic.php?t=172 (2-0-7 details of BER%)
http://www.xm411.com/phpbb/viewtopic.php?t=4092 (cable splicing instructions)

BTW: The little magnetic 'chicklet' antennas that my Roady2 uses appear to be 1/4 Wavelengh horizontally polarized antennas. A full wavelength at this frequency (2.3Ghz) is just under 5". The "Home Kit" antenna appears to be a 5/8 Wavelength antenna (about 3") :brow
I wasn't sure how accurate the XM's built in signal strength receiver was compared to a nice signal strength meter and it's been SO long since I've used my XM SkiFi2, I don't even recall what it shows anymore... ;) Nice tips at those links, thanks!

[cjack]

True... they set the length of the cable for installation in cars, but that length was taken into account in the design for the best reception. You can definitely shorten the length of the cable, signal lost won't stop the radio from working. I've done it for a couple people, but you do lose some signal strength - the XM receivers showed a 1 bar drop. I'm not sure what you are using to measure signal, and there are a lot of factors involved in signal strength. I don't have a signal strength meter to get accurate measures. The discussion on impedance is explained better here http://en.wikipedia.org/wiki/Antenna_(electronics), excerpt:

Impedance
"Impedance" is analogous to refractive index in optics. As the electric wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance. At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.

Complex impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match.

While this is all true, it doesn't answer the question of whether the antenna and receiver input are matched to the feedline and if they are, then the length of the coax makes no difference. Except that longer coax runs have more loss.
Then if you throw in the preamp at the antenna, the impedance question becomes even more unknown.

[wmubrown]

While this is all true, it doesn't answer the question of whether the antenna and receiver input are matched to the feedline and if they are, then the length of the coax makes no difference. Except that longer coax runs have more loss.
Then if you throw in the preamp at the antenna, the impedance question becomes even more unknown.
Ah... in an earlier post I thought I'd passed along a tidbit from an XM engineer that they use the cable for fine tuning the antennae to the receiver to cut down some of the parts necessary in the receiver for tuning. Wish I could find that Email, and the guys address, but I can't seem to locate it. I didn't think to ask if the antennae has a preamplifier, I was just concerned with whether I could shorten the cable or not. He said he didn't see any problem with that, but that it would reduce the signal strength "a bit". I didn't ask for any further details, that was good enough for me.

FWIW, I bought the Terk XM antennae (the micro sized one) and modified it as a test. It's end connector (plugs into the XM receiver) was easily diassembled so I could cut the cable, and reinstall the connector - made for a very clean installation, no splice in the cable :)

[cjack]

Ah... in an earlier post I thought I'd passed along a tidbit from an XM engineer that they use the cable for fine tuning the antennae to the receiver to cut down some of the parts necessary in the receiver for tuning. Wish I could find that Email, and the guys address, but I can't seem to locate it. I didn't think to ask if the antennae has a preamplifier, I was just concerned with whether I could shorten the cable or not. He said he didn't see any problem with that, but that it would reduce the signal strength "a bit". I didn't ask for any further details, that was good enough for me.

FWIW, I bought the Terk XM antennae (the micro sized one) and modified it as a test. It's end connector (plugs into the XM receiver) was easily diassembled so I could cut the cable, and reinstall the connector - made for a very clean installation, no splice in the cable :)

That answer about tuning the antenna to the receiver by changing the length is very valid I think. That would imply that there is no preamp and the antenna is some impedance other than the 75 ohms of the coax. A true 1/4 wave antenna would be 37 ohms on a ground plane, if that's what they are. I have no idea what these truly are, but in order to tune a feed line with a mismatched antenna at it's end at the receiver would require at least two and maybe three tuning elements. Adjusting the length of the feedline is a way of presenting a more favorable impedance to tune. It doesn't change the SWR though. So you are still stuck with that loss issue. It is possible to tune the antenna with two elements, to the coax, at the antenna. Lots of CB antennas have a trimmer in them to do this. I would expect that for the general public using XM radio, it is better to make it simple and just discourage mods.
About the preamp. I use a GPS receiver from HP (they use these in Cell phone towers) for a time and frequency standard in ham radio. It uses a GPS antenna with a preamp in it and the small coax, although long and has much loss, the signal is great at the receiver. I wonder if there is an optional amplified antenna out there somewhere for XM.

[BradfordBenn]

I asked the engineers at work today, and unfortunately I left the notes I took at work, but basically the "stock" XM cables are x wavelengths. The data rate is 2.3gHz on the cable, putting a solder splice in is about 3dB of attenuation and at -12dB one typically loses signal. He said the best thing to do is if shortening a cable is to do either half, 1/4 or 1/8 length.

[bmwsoldat]

ok,
to those who have done it.
did you just cut and splice from the center or where did you cut the cable?
i have had a couple of the anntenas go bad on me and was wondering where you guys did your splicing/cutting.
i was going to try to cut a couple of inches off either side near the connectors.
reason being is this: i generally notice that that is where problems surface. where a cable bends it is at its weakest point.

IF ANYONE KNOWS WHERE I CAN FIND THE END CONNECTOR THAT WOULD BE FANTASTIC.
i am not really sure what type it is, i have delt with allot of differant ends just not sure what make and model it is doesnt look like you could get it at radio shed either.

[bmwmick]

:stick I made one splice, about 3" from the connector and about 3" from the antenna. Total length is now about 6". One splice. No difference in signal strength.

[cjack]

IF ANYONE KNOWS WHERE I CAN FIND THE END CONNECTOR THAT WOULD BE FANTASTIC.
i am not really sure what type it is, i have delt with allot of differant ends just not sure what make and model it is doesnt look like you could get it at radio shed either.

What's it look like?
Picture?

[bmwmick]

What's it look like?
Picture?


Jack,
I think they all use a style of MCX connectors......
http://www.connectorcity.com/index.php?section=products&subcategory=MCX

[cjack]

Jack,
I think they all use a style of MCX connectors......
http://www.connectorcity.com/index.php?section=products&subcategory=MCX

OK. So there you are bmwsoldat. It's probably easier to do the neat solder splice than deal with the crimp connector with out a crimping die. And seems to work well.

[bmwsoldat]

OK. So there you are bmwsoldat. It's probably easier to do the neat solder splice than deal with the crimp connector with out a crimping die. And seems to work well.

:dance
i can see what you saying! i noticed the small size and it seems like a large pain in the butt!
:bikes