Suggestions ppl...

01-11-2002

Ok...

I'm sure some of you have seen my van. I now have a RangeLan 7400 card that has a really nice "Poor Man's" spectrum analyzer site surveying tool.

So, my radio could is up to 5 and I want to connect all of these to external antennas. However, a van with 5 plus antennas draws attentiona and it gets costly at about $80 per 6dbd antenna.

My solution, in theory, is to buy a 5 port splitter / combiner. This way, I can drive 5 radios off my existing antenna.

MY QUESTION: Do you think the radios will interfer with each other to the point that nothing will work? Of course I don't have to run each radio's tools at the same time. But with NS tossing out beacons and my RangeLan listening for traffic, if they are both on the same antenna, do you forsee problems? My initial thoughts are that there won't be a problem. After all, what is the REAL difference in running 2 antenna's 1 or 2 feet apart and running 2 radios on the same antenna?

Also, do you think I'll loose too much db???

Thanks ppl,
Tron Of Borg

01-11-2002

Not a good idea...

At least not if your talking about 2 way Radio's? (vs. reciever only).

1.) Antenna are designed to produce a radio signal based on a voltage supplied to the antenna coil by the transmitter, inversely a radio wave picked up by the antenna is converted to a voltage by the antenna coil.

2.) Connecting multiple 2 way radio's to the same antenna will cause the transmitter to burn out ALL of the connected receivers that are powered on the minute you key up the mike on the transmitter, that is if they are of any decent quality.

This is because the signal sent out the antenna cable would be sent into the others and is actually voltage (power) that drives the antenna coil which produces the radio wave output from the antenna.

3.) Antenna have different designs based on transmitter/receiver thus different transmitters/receivers require different antenna designs so feeding any old tranmitter/receiver signal to any old antenna will at best degrade the quality and performance and in a lot of cases may not work at all, in some cases could even damage the transmitter/receiver!

In the end, you need an antenna for each...

Hope This Helps...

~GeekDude

01-11-2002

Then again your probably not talking about 2 way radios huh...

01-11-2002

GeekDude,
Of course the cards are two way radios! You were right in your first analysis. They are low-powered, to be sure, but you are still talking about putting directly transmitted RF down the RX side of the card. Ouch!

Tron,
I'm not sure it would help, but some high powered commercial and ham gear solve similar types of problems using "resonant cavities." No, I'm not talking about picking up the local AM station in your teeth! These things are big cans, with tuned RF elements, that let rcvrs and xmitrs play nice together. I've seen some in the 450 MHz range that are about 6" in diameter and 2' long. Many times they are used to seperate the TX and RX sides on car-to-car repeaters.

In this freq range, I bet you could build some out of juice or coffee cans.

It might require that you set each of the cards on one channel each. I'd suggest starting with an ARRL manual.

Cheers,
Thorn

01-12-2002

Tron,

In most repeater installations I've seen, a phasing harness (aka combiner or splitter) is used to be able to connect both TX and RX sections to the same antenna. Basically, this box detects RF from a transmitter, and instantaneously isolates the other rigs antennas (or is it antennae?) from it - otherwise you're talking bye-bye.

Cavities are used most often when the TX and RX frequencies are very close - one local repeater used 159.250MHz for TX and 158.750MHz for RX. Most amateur repeaters in VHF use 600kHz shift. In the commercial band, at least where I live, the spacing is 4.6MHz in VHF and 10MHz in UHF.

In any case, I've seen eight transmitters (from a TETRA BTS) wired to a single antenna, working very happily. The problem you'll find is that at high frequencies, the cavities need to be VERY high quality, for example the ones used in TETRA digital radio cells can cost a few thousand $$. Otherwise you run into losses.

I personally have 8 antennas in my van (2 for GPS, one more active GPS receiver+antenna, 2 for GSM, 2 for TETRA, 1 for PMR VHF+UHF) and one more is coming for stumbling :-). I'll send you some pics if U want, it's true it grabs attention, but most people will just think you're a telco, or a MiB hehehe.

Cheers,

Mother

01-12-2002

Just curious. Have you ever had a cop stop you for traffic or possibly a fender bender? I'm curious what the reaction to all the gear is? I have some in my suv but it doesn't look like a 911 comm center.

01-12-2002

At one point in time, I had 6 antennas on my Tracker (which since burnt to a crisp). Radio, CB, Scanner, Mobile Phone, Work Cell Phone, 2m Ham. I never got pulled over for it...but it did make my vehicle a target to theft, which I sorely found out one morning when all my equipment, except the stereo were gone.

More antennas suggests nice, expensive equipment.

-A.G.-

01-13-2002

Hmmmm...it is true that such setup attracts the attention of thieves, but there are workarounds. I have a few small CO2 cylinders which can be discharged by electrical trigger, soon to be remotely controlled via GSM (I'm currently building a GSM alarm system, which will let you know when your car is disturbed via call and SMS). It's not a deadly deterrent, but it gives a hell of a scare! I'm sure most thieves would just run away...

Regarding being pulled over, I have been asked once about all the gear, which was quickly excused by being a member of my local volunteer fire dept. I even gave the cop a demo of the new TETRA digital rigs we have :-)

Anyways, I think that if you have some other program running in the background, like AutoRoute or whatever, you can claim to be using THAT. I don't believe that having a laptop on your passenger seat is 'probable cause' for a search or seizure. Alt+F4 gets rid of NS in a second. Ah, an extra Enter to save changes.

Cheers,

Mother

01-24-2002

...but it'll be <ahem> a bit more expensive than your $80 6dbd antennas. A six antenna mount, using our SI 5015 antennas, giving you a azimuth -3dbd of 50 degrees, 15 dbi of gain with 30 to 40 db of seperation between antennas. You can do tx and rx on each antenna but you'll need a good duplexer per antenna.

http://www.swedcom.com/files

click on si5015b.pdf

Now just cut a hole in the roof of your van and put the whole thing on a hydraulic lift so that you're a little bit less suspicious looking...

01-25-2002

Heck, I want me one of those news vans with a pneumatic 40-foot mast! Plenty of room for all sorts of goodies! My vehicle already looks like a porcupine...

01-25-2002

...but look at it this way.

For the math, lets say that 1db is a multiplier of 1 and 10db is a multiplier of 10, etc.

Lets say I have 10V worth of signal running out the radio into a 10bd antenna. That means that that 10V worth of signal is amplified by 10db which would render a signal of 100V worth of signal. This is much more then 10V worth of signal would produce with a 1db gain (10V worth of signal). Of course, I'm tossing out signal loss, etc.

Now, that is the transmit side. How about reversing it for the receive antenna. (I say receive antenna because I'd have to have these antennas somewhat close together and the TX sig of one antenna will be the RX of a neighboring antenna.)

We have a 100V worth of signal being picked up by an antenna with 10db worth of gain. Thats now 1000V worth of signal going to that radio. If the antenna was just a 1db antenna, then you still have 100V worth of signal hitting the radio.

My point is, with the gain in the antennas, wouldn't that just increase the signal above that which the radio would be getting if they were on the same cable? Also, what about the sensitivity of the radios, this would seem to make it worse if the radios were really sensitive.

NOW FOR MY ARGUMENT AGAINST MYSELF.
How can you end up with a stronger signal then the one you TX without adding energy? My assumption is that the db gain is linear when I know it is a log-scale (or inverse log??). I just don't know for sure how much impact this has over it. But then again, I think every 3db is a doubling of power.

(someone...stop me please!)

Tron Of Borg(XPlog)

01-25-2002

Tron,
There is an inverse square (or log, I forget) to the signal here, which results in a major drop in the air gap between the antennae. If you have two high gain antennae, set up close, say in the same room for testing, you have to attenuate the signal to prevent overloading and possibly causing damage to the reviever.

Rob Flickenger, he of the infamous Pringle's Can Antenna, has got some of the computations for this on oreilly.net. Look for the article on Long Distance 802.11 Links.

Cheers,
Thorn

03-12-2002

Antenna gain (expressed in dB) does not mean that an antenna is adding energy to a signal. It does mean that one design might direct more energy *in a particular direction* than another design. Of course, it will also direct less energy in other directions. So, if you are looking for a single number to express gain, you always measure antenna gain *on beam*. A complete characterization of an antenna measures gain in all directions. for a directional antenna, gain is positive (=stronger signal) in some directions, but negative (=weaker signal) in other directions.

Antenna gain is in comparison to some sort of a reference antenna. There are two common references: an isotropic antenna (a theoretical animal that sprays energy equally in all directions), and a simple quarter wave dipole. When antennas are designed and tested, they are compared to dipoles (which are some directional on their own). Typically, manufacturers state antenna gain relative to isotropic (even though they never tested relative to isotropic, since no such thing exists), since the gain comes out 1.7 dB higher than compared to dipole.

03-12-2002

LOL

After I posted that last post of mine, it dawned on me that you can never receive more power then what you put out barring external amplification.

In any case, my question was stupid and there is no EDIT/DELETE option!

In any case, I never responded hoping this thread would die! Guess Not!

DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE

Tron Of Borg

03-13-2002

I can actually think of one isotropic radiator, but it's rather impractical... That would be the Sun (or any normal star for that matter) It radiates in ALL directions. A standard dipole reference has a doughnut shape radiation pattern (or is it a bagel shaped radiation pattern?).

<da.nyet>

01-11-2002	#1 (permalink)
Posts: n/a	Suggestions ppl... Ok... I'm sure some of you have seen my van. I now have a RangeLan 7400 card that has a really nice "Poor Man's" spectrum analyzer site surveying tool. So, my radio could is up to 5 and I want to connect all of these to external antennas. However, a van with 5 plus antennas draws attentiona and it gets costly at about $80 per 6dbd antenna. My solution, in theory, is to buy a 5 port splitter / combiner. This way, I can drive 5 radios off my existing antenna. MY QUESTION: Do you think the radios will interfer with each other to the point that nothing will work? Of course I don't have to run each radio's tools at the same time. But with NS tossing out beacons and my RangeLan listening for traffic, if they are both on the same antenna, do you forsee problems? My initial thoughts are that there won't be a problem. After all, what is the REAL difference in running 2 antenna's 1 or 2 feet apart and running 2 radios on the same antenna? Also, do you think I'll loose too much db??? Thanks ppl, Tron Of Borg

01-11-2002	#2 (permalink)
Posts: n/a	Carefull... Not a good idea... At least not if your talking about 2 way Radio's? (vs. reciever only). 1.) Antenna are designed to produce a radio signal based on a voltage supplied to the antenna coil by the transmitter, inversely a radio wave picked up by the antenna is converted to a voltage by the antenna coil. 2.) Connecting multiple 2 way radio's to the same antenna will cause the transmitter to burn out ALL of the connected receivers that are powered on the minute you key up the mike on the transmitter, that is if they are of any decent quality. This is because the signal sent out the antenna cable would be sent into the others and is actually voltage (power) that drives the antenna coil which produces the radio wave output from the antenna. 3.) Antenna have different designs based on transmitter/receiver thus different transmitters/receivers require different antenna designs so feeding any old tranmitter/receiver signal to any old antenna will at best degrade the quality and performance and in a lot of cases may not work at all, in some cases could even damage the transmitter/receiver! In the end, you need an antenna for each... Hope This Helps... ~GeekDude

01-11-2002	#3 (permalink)
Posts: n/a	Ummm... Then again your probably not talking about 2 way radios huh...

01-12-2002	#5 (permalink)
Posts: n/a	Repeater antennas.... Tron, In most repeater installations I've seen, a phasing harness (aka combiner or splitter) is used to be able to connect both TX and RX sections to the same antenna. Basically, this box detects RF from a transmitter, and instantaneously isolates the other rigs antennas (or is it antennae?) from it - otherwise you're talking bye-bye. Cavities are used most often when the TX and RX frequencies are very close - one local repeater used 159.250MHz for TX and 158.750MHz for RX. Most amateur repeaters in VHF use 600kHz shift. In the commercial band, at least where I live, the spacing is 4.6MHz in VHF and 10MHz in UHF. In any case, I've seen eight transmitters (from a TETRA BTS) wired to a single antenna, working very happily. The problem you'll find is that at high frequencies, the cavities need to be VERY high quality, for example the ones used in TETRA digital radio cells can cost a few thousand $$. Otherwise you run into losses. I personally have 8 antennas in my van (2 for GPS, one more active GPS receiver+antenna, 2 for GSM, 2 for TETRA, 1 for PMR VHF+UHF) and one more is coming for stumbling :-). I'll send you some pics if U want, it's true it grabs attention, but most people will just think you're a telco, or a MiB hehehe. Cheers, Mother

01-12-2002	#6 (permalink)
Posts: n/a	Inside the "wiredvan" Just curious. Have you ever had a cop stop you for traffic or possibly a fender bender? I'm curious what the reaction to all the gear is? I have some in my suv but it doesn't look like a 911 comm center.

01-11-2002	#4 (permalink)
Posts: n/a	GeekDude, Of course the cards are two way radios! You were right in your first analysis. They are low-powered, to be sure, but you are still talking about putting directly transmitted RF down the RX side of the card. Ouch! Tron, I'm not sure it would help, but some high powered commercial and ham gear solve similar types of problems using "resonant cavities." No, I'm not talking about picking up the local AM station in your teeth! These things are big cans, with tuned RF elements, that let rcvrs and xmitrs play nice together. I've seen some in the 450 MHz range that are about 6" in diameter and 2' long. Many times they are used to seperate the TX and RX sides on car-to-car repeaters. In this freq range, I bet you could build some out of juice or coffee cans. It might require that you set each of the cards on one channel each. I'd suggest starting with an ARRL manual. Cheers, Thorn

01-12-2002	#7 (permalink)
Posts: n/a	Antennas. At one point in time, I had 6 antennas on my Tracker (which since burnt to a crisp). Radio, CB, Scanner, Mobile Phone, Work Cell Phone, 2m Ham. I never got pulled over for it...but it did make my vehicle a target to theft, which I sorely found out one morning when all my equipment, except the stereo were gone. More antennas suggests nice, expensive equipment. -A.G.-

01-13-2002	#8 (permalink)
Posts: n/a	Burglar's honeypot Hmmmm...it is true that such setup attracts the attention of thieves, but there are workarounds. I have a few small CO2 cylinders which can be discharged by electrical trigger, soon to be remotely controlled via GSM (I'm currently building a GSM alarm system, which will let you know when your car is disturbed via call and SMS). It's not a deadly deterrent, but it gives a hell of a scare! I'm sure most thieves would just run away... Regarding being pulled over, I have been asked once about all the gear, which was quickly excused by being a member of my local volunteer fire dept. I even gave the cop a demo of the new TETRA digital rigs we have :-) Anyways, I think that if you have some other program running in the background, like AutoRoute or whatever, you can claim to be using THAT. I don't believe that having a laptop on your passenger seat is 'probable cause' for a search or seizure. Alt+F4 gets rid of NS in a second. Ah, an extra Enter to save changes. Cheers, Mother

01-24-2002	#9 (permalink)
Posts: n/a	this might help... ...but it'll be <ahem> a bit more expensive than your $80 6dbd antennas. A six antenna mount, using our SI 5015 antennas, giving you a azimuth -3dbd of 50 degrees, 15 dbi of gain with 30 to 40 db of seperation between antennas. You can do tx and rx on each antenna but you'll need a good duplexer per antenna. http://www.swedcom.com/files click on si5015b.pdf Now just cut a hole in the roof of your van and put the whole thing on a hydraulic lift so that you're a little bit less suspicious looking...

01-25-2002	#10 (permalink)
Posts: n/a	Heck, I want me one of those news vans with a pneumatic 40-foot mast! Plenty of room for all sorts of goodies! My vehicle already looks like a porcupine...

01-25-2002	#11 (permalink)
Posts: n/a	Ok..I understand about the voltage... ...but look at it this way. For the math, lets say that 1db is a multiplier of 1 and 10db is a multiplier of 10, etc. Lets say I have 10V worth of signal running out the radio into a 10bd antenna. That means that that 10V worth of signal is amplified by 10db which would render a signal of 100V worth of signal. This is much more then 10V worth of signal would produce with a 1db gain (10V worth of signal). Of course, I'm tossing out signal loss, etc. Now, that is the transmit side. How about reversing it for the receive antenna. (I say receive antenna because I'd have to have these antennas somewhat close together and the TX sig of one antenna will be the RX of a neighboring antenna.) We have a 100V worth of signal being picked up by an antenna with 10db worth of gain. Thats now 1000V worth of signal going to that radio. If the antenna was just a 1db antenna, then you still have 100V worth of signal hitting the radio. My point is, with the gain in the antennas, wouldn't that just increase the signal above that which the radio would be getting if they were on the same cable? Also, what about the sensitivity of the radios, this would seem to make it worse if the radios were really sensitive. NOW FOR MY ARGUMENT AGAINST MYSELF. How can you end up with a stronger signal then the one you TX without adding energy? My assumption is that the db gain is linear when I know it is a log-scale (or inverse log??). I just don't know for sure how much impact this has over it. But then again, I think every 3db is a doubling of power. (someone...stop me please!) Tron Of Borg(XPlog)

01-25-2002	#12 (permalink)
Posts: n/a	Tron, There is an inverse square (or log, I forget) to the signal here, which results in a major drop in the air gap between the antennae. If you have two high gain antennae, set up close, say in the same room for testing, you have to attenuate the signal to prevent overloading and possibly causing damage to the reviever. Rob Flickenger, he of the infamous Pringle's Can Antenna, has got some of the computations for this on oreilly.net. Look for the article on Long Distance 802.11 Links. Cheers, Thorn

03-12-2002	#13 (permalink)
Posts: n/a	antenna gain Antenna gain (expressed in dB) does not mean that an antenna is adding energy to a signal. It does mean that one design might direct more energy in a particular direction than another design. Of course, it will also direct less energy in other directions. So, if you are looking for a single number to express gain, you always measure antenna gain on beam. A complete characterization of an antenna measures gain in all directions. for a directional antenna, gain is positive (=stronger signal) in some directions, but negative (=weaker signal) in other directions. Antenna gain is in comparison to some sort of a reference antenna. There are two common references: an isotropic antenna (a theoretical animal that sprays energy equally in all directions), and a simple quarter wave dipole. When antennas are designed and tested, they are compared to dipoles (which are some directional on their own). Typically, manufacturers state antenna gain relative to isotropic (even though they never tested relative to isotropic, since no such thing exists), since the gain comes out 1.7 dB higher than compared to dipole.

03-12-2002	#14 (permalink)
Posts: n/a	Dam..someone brought this back up! LOL After I posted that last post of mine, it dawned on me that you can never receive more power then what you put out barring external amplification. In any case, my question was stupid and there is no EDIT/DELETE option! In any case, I never responded hoping this thread would die! Guess Not! DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE DIE Tron Of Borg

03-13-2002	#15 (permalink)
Posts: n/a	I can actually think of one isotropic radiator, but it's rather impractical... That would be the Sun (or any normal star for that matter) It radiates in ALL directions. A standard dipole reference has a doughnut shape radiation pattern (or is it a bagel shaped radiation pattern?). <da.nyet>

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