Mobile Co-Phasing

[Don_Burke]

It ain't necessarily so, null value equals zero in any math book.

That is true enough, but since achieving a partial null was the whole point of the array, considering a null to be a disadvantage is indeed missing the point.

"Open road CB is not like two meters and treating it the same can take you down the wrong path."

Who said I was treating it like 2M?

I did.

When you stated that the purpose of the array was to fill in the sides of the pattern, it was the only conclusion that I could see.

Here is what you said:

The CB "Twin Truckers" approach is the worst hoax ever perpetrated and is sheer fallacy, no way can an end fire array counteract the asymmetrical ground plane effect of a vehicle body. No way can proper spacing be achieved on 11M and in any case although it can on VHF still it's pretty stupid considering the fact it's MOBILE. Turn the vehicle and you rotate the pattern, DUH!

Since the twin trucker antenna array is a broadside array, there would seem to be some confusion.

It makes fighting it out on channel 19 look like the waste of time it is although it has certain advantages, like more truckers. That's why I can't put down CB entirely, my friend Jim W2RXR being a trucker has his HF/VHF/UHF ham rig and a CB in the cab.

There are quite a few of those. Out on the road there really is no substitute for a CB rig, assuming you can wade through the noise.

 

[N_Jay]

OK, little industry semantics lesson.

No working RF engineer would interpret an antenna "null" as a perfect null (0).

They are RELATIVE NULLS, with gains (negative gain figures) significantly lower than the average gain of the antenna.

Anyone who argues you are WRONG using the term by either implying they are not truly 0 is just showing HIS LACK OF KNOWLEDGE!:roll: :evil:

 

[k9rzz]

"Personally, I think it would be a fun experiment."

Personally I think reinventing the square wheel is a gross waste of time..

I don't know what a 'square wheel' is, but certainly building an antenna system and playing around with the dimensions to get a personal "feel" for antenna performance.

How do you know how bake cookies unless you do it?, how do you know how to phase antennas and see what they can or can't do for you unless you do it?

There is a BIG difference between hands on experience and 'book knowledge', I think it's good to have BOTH.

John K9RZZ

 

[N_Jay]

I don't know what a 'square wheel' is, but certainly building an antenna system and playing around with the dimensions to get a personal "feel" for antenna performance.

How do you know how bake cookies unless you do it?, how do you know how to phase antennas and see what they can or can't do for you unless you do it?

There is a BIG difference between hands on experience and 'book knowledge', I think it's good to have BOTH.

John K9RZZ

The issue is;
. . . . . .
Without a good, valid method to test your results you are as likely (or even more likely) to build myths and superstitions rather than knowledge.

It would be like baking cookies and then feeding them to a hungry dog to see which are better.

 

[fmulder13]

Not as much as you might think, but the message that I get is that co-phasing is not at all sensical for what I want to accomplish. From what I'd observed on police cruisers it seemed as though they might be using co-phasing for better radio performance, but it looks as though that is not the case.

I do remember someone pointing out that the police radios are "considerably better" at receiving then scanners. Why is that? Is there any way to "bridge the gap?"

 

[w0fg]

Police (commercial business band) radios are made to do one thing and do it very well. Scanners are made to do many things reasonably well. Such design criteria are usually mutually exclusive.

 

[SLWilson]

Pro2096

If his Pro2096 is like mine, it isn't worth a darn on VHF Hi RX. No matter how many antennas he uses on it.

On 800Mhz trunked, it the RX is OK, but, VHF Hi and Low just aren't there. So, I use my Uniden to hear the local Hi & low band stuff. Just use the OVER-PRICED 2096 for trunked radio.

Steve/KB8FAR

 

[k9rzz]

The issue is;
. . . . . .
Without a good, valid method to test your results you are as likely (or even more likely) to build myths and superstitions rather than knowledge.

It would be like baking cookies and then feeding them to a hungry dog to see which are better.

C'mon ... you don't have to measure sig strength to 0.1 db to get a feel if something is better or worse than it was before. A keen ear is priceless. You'll know if a signal has less noise on it or not, which is what the end goad is, isn't it?

Knowing how to bake cookies is fine, but if you can't actually make them, even if to just feed the dogs, then everybody stays hungry.

John K9RZZ

 

[N_Jay]

C'mon ... you don't have to measure sig strength to 0.1 db to get a feel if something is better or worse than it was before. A keen ear is priceless. You'll know if a signal has less noise on it or not, which is what the end goad is, isn't it?

Knowing how to bake cookies is fine, but if you can't actually make them, even if to just feed the dogs, then everybody stays hungry.

John K9RZZ

Where did I sat 0.1 dB.

I challenge most scanners to resolve even 3dB.

Absolute signal strength is only one aspect.

Lets assume you can get better than 3dB with the squelch knob or the S-meter.

How are you going to resolve directionality (A major effect of multiple element antennas)??
How are you going to resolve anomalies in gain over frequency (Another major expected effect of a complex RF network)???

If you don't know how to see whet you are looking for how are you going to know when you have it.

Back to the rain dance analogy. Myths and superstitions!

 

[w0fg]

N Jay is right. A 3db loss in received signal in squelched FM mode is going to be imperceptible.

 

[k9rzz]

"How are you going to resolve directionality (A major effect of multiple element antennas)??"

-> I thought that was the goal. "I want to see if I can't pick up my local PD when they're not using the repeater on their portables." If he's already got one antenna (omni directional assumed), and he's trying to hear weaker stations, he's either got to go higher or get some gain. He NEEDS directionality.

"How are you going to resolve anomalies in gain over frequency (Another major expected effect of a complex RF network)???"

-> His question was regarding his local police department. He wasn't specific on what frequency/frequencies they run (unless that got lost in the jumble of posts after). As long as they run on the same band (VHF or UHF), the setup will work. If he's got 10 side lobes on one frequency and a dozen on another ... WHO CARES !

"If you don't know how to see whet you are looking for how are you going to know when you have it."

-> If he can HEAR some of the mobiles without the repeater ... goal accomplished, no matter what signal strength they are. Your ears will do the measuring.

"N Jay is right. A 3db loss in received signal in squelched FM mode is going to be imperceptible."

-> If 3db brings you out of the noise and be copied, that's not imperceptible.

John K9RZZ

 

[N_Jay]

With very little additional effort I could have my quotes formatted properly.
(But why bother since you will not even both to use the quote feature to make it easier for others.)

"How are you going to resolve directionality (A major effect of multiple element antennas)??"

-> I thought that was the goal. "I want to see if I can't pick up my local PD when they're not using the repeater on their portables." If he's already got one antenna (omni directional assumed), and he's trying to hear weaker stations, he's either got to go higher or get some gain. He NEEDS directionality.
John K9RZZ

1) to get any idea if you are getting directional gain, you have to rotate the whole assembly, or are you just going to guess where the peaks and nulls are?

2) The peaks and nulls are likely to be in different places for different frequencies

"How are you going to resolve anomalies in gain over frequency (Another major expected effect of a complex RF network)???"

-> His question was regarding his local police department. He wasn't specific on what frequency/frequencies they run (unless that got lost in the jumble of posts after). As long as they run on the same band (VHF or UHF), the setup will work. If he's got 10 side lobes on one frequency and a dozen on another ... WHO CARES !
John K9RZZ

I guess you can test every frequency you are interested in, and then retest next time you add a frequency.:roll:

"If you don't know how to see whet you are looking for how are you going to know when you have it."

-> If he can HEAR some of the mobiles without the repeater ... goal accomplished, no matter what signal strength they are. Your ears will do the measuring.
John K9RZZ

The problem is with FM you rarely know how much above full quieting or below threshold a signal is.
You ears are REALLY bad instruments for these measurements.

"N Jay is right. A 3db loss in received signal in squelched FM mode is going to be imperceptible."

-> If 3db brings you out of the noise and be copied, that's not imperceptible.

John K9RZZ

As I have said, 3 dB will not make bring a signal up enough to turn a unusable signal into an acceptable one.

But you seems to believe otherwise. Maybe you have a step attenuator so you can listen to the difference, or maybe you are guessing!

(I'm guessing, you are guessing)

Go have fun. In the end, I bet you will have learned little and further strengthened misconceptions that get in the way of real learning.

 

[jonny290]

FM is specifically engineered to separate signal intelligibility from signal strength.

i have to sometimes correct the newer local hams that come from the CB or sideband side and think that signal is just modulation * power * antenna. It doesn't work like that on 2 meters.

 

[Raccon]

Where did I sat 0.1 dB.

I challenge most scanners to resolve even 3dB.

He never said you did say that - it was a (made-up) hyperbole to stress his point.

 

[N_Jay]

He never said you did say that - it was a (made-up) hyperbole to stress his point.

And that point was?

 

[k9rzz]

Found this interesting site that has the radiation pattern of _CB_ antennas plotted - single vs phased.

http://signalengineering.com/ultimate/mobile_antennas.html

vs

It would be interesting to see how this plays out on VHF. Hmmmm ... that would be an interesting experiment, don't 'cha think?

I understand what 'yall are saying, but radio is for fun, and personally, I find it fun experimenting with various antennas. Am I wasting my time, I don't think so, but as long as I'm enjoying myself, that's what it's all about.

73!

John K9RZZ

 

[Don_Burke]

Found this interesting site that has the radiation pattern of _CB_ antennas plotted - single vs phased.

http://signalengineering.com/ultimate/mobile_antennas.html

vs

It would be interesting to see how this plays out on VHF. Hmmmm ... that would be an interesting experiment, don't 'cha think?

I understand what 'yall are saying, but radio is for fun, and personally, I find it fun experimenting with various antennas. Am I wasting my time, I don't think so, but as long as I'm enjoying myself, that's what it's all about.

The thing that is missing is the distance between the antennas.

There are plenty of patterns for various vertical systems on http://www.fccinfo.com and one that shows two verticals fed in phase with the towers a bit over one half wave apart can be found at WRVA in Richmond.

I have not found a station with the same phasing and the towers about 70 degrees apart. That would be pretty close to what twin trucker antennas are trying to do.

KD4OSP

 

[ohiodesperado]

The other thing not discussed above is this is a CAR and not a semi tractor tailor.

There is a bit of difference between a 12 by 7 vehicle that you are mounting antennas on in the center of the long axis and a vehicle that it 8 by 80 and the antennas are mounted on the front 8 feet of the long axis.

Point is this, co-phased arrays are about transmitting not receiving.

It's hard enough to get a phased array going on a vehicle to begin with on the transmit side and have it do any good.

The idea of trying to get it to work in the same manner on receive where you are dealing with microvolts of electricity that if the phasing is not absolutely correct can cancel it's self out.

Here's what I mean. If a received signal come in on two antenna's that are spaced apart. The signal will travel down the coax at two different points on the same time line. Unless the cable lengths and the direction that you are listening from is perfect and all the timing is corrected, that different in the time that the signal reaches that TEE connector, the two signals, being out of phase of each other ever so slightly can cause them to attenuate each other and you end up with LESS received signal and not more.

Trying to get into this too far is pointless. Look at like two cars that are side by side on a curvy road that are going to same direction. Then chain the cars together. As long as they are both going the right speed, hitting the corners at exactly the right time they can help each other along and go really fast. The minute that either of them varies from it's optimium course and speed it slows them BOTH up and things get slow quick.

 

[Don_Burke]

Point is this, co-phased arrays are about transmitting not receiving.

In the CB world, I strongly disagree with this statement. The forward gain of a two antenna array fed in phase is marginal at best. The side rejection, on the other hand, can be significant.

It's hard enough to get a phased array going on a vehicle to begin with on the transmit side and have it do any good.

The idea of trying to get it to work in the same manner on receive where you are dealing with microvolts of electricity that if the phasing is not absolutely correct can cancel it's self out.

With microvolts or megavolts the phasing is the same.

Here's what I mean. If a received signal come in on two antenna's that are spaced apart. The signal will travel down the coax at two different points on the same time line. Unless the cable lengths and the direction that you are listening from is perfect and all the timing is corrected, that different in the time that the signal reaches that TEE connector, the two signals, being out of phase of each other ever so slightly can cause them to attenuate each other and you end up with LESS received signal and not more.

The transmitted signal is subject to all of the same distance tolerances.

"Ever so slightly" just rotates the pattern. We are talking about feet of error to get massive problems.

Trying to get into this too far is pointless. Look at like two cars that are side by side on a curvy road that are going to same direction. Then chain the cars together. As long as they are both going the right speed, hitting the corners at exactly the right time they can help each other along and go really fast. The minute that either of them varies from it's optimium course and speed it slows them BOTH up and things get slow quick.

This analogy has no application in antennas.

 

[N_Jay]

. . . . .
Point is this, co-phased arrays are about transmitting not receiving.

It's hard enough to get a phased array going on a vehicle to begin with on the transmit side and have it do any good.

The idea of trying to get it to work in the same manner on receive where you are dealing with microvolts of electricity that if the phasing is not absolutely correct can cancel it's self out.
. . . .. .

Why is it so hard for people to understand that with very few exceptions, antennas work EXACTLY the same in both transmit and receive.:roll: :roll: :roll: