Mobile Co-Phasing

[jonny290]

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.

holy


my mind has been blown

 

[Raccon]

And that point was?

Just read his post again to which you responded that. I believe what he is saying that it's overkill to perform a complex and time-consuming, perhaps costly, measurement exercise when he thinks the result can be determined by other means.

 

[N_Jay]

Just read his post again to which you responded that. I believe what he is saying that it's overkill to perform a complex and time-consuming, perhaps costly, measurement exercise when he thinks the result can be determined by other means.

That is the problem; "he thinks".

That is the center-point of the whole discussion.

 

[ohiodesperado]

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:

I am not questioning this. I do agree, but what I am talking about is the effect is going to be more pronuouced in receive than in transmit.

The reason that a semi truck experiences the side null is that the signal coming from either side reaches the oppsite side 1/4 wave later at 27 Mhz (about 9 feet) I properly setup co-phasing harness is 1/2 wave electrically. So the signal gets the the center point out of phase of each other and attenuates the side signal. The signal that is coming from the front or back reaches the antennas ath the same time and not attenuation occurs.

Now this is for a radio that operates in a sepcific frequency range that is very narrow from 26.965 to 27.405 Mhz.
Now we enter the scanner into the mix. We are no longer talking about a few Khz of band we are talkinig aobut a receiver that reasonably receives from 25 Mhz to at minimum 512 Mhz and realistically to 900 Mhz. As the frequency changes the phasing is going to change as well. On a semi truck that 9 feet is a 1/4 wave length, but at 150 Mhz it's now over two full wavelengths and 400 Mhz it's even greater. The signal attenuation in the two cables is going to change, there will be slight differences in the signal levels received at the two antenna's due to atmospheric losses (yes it's slight, but all this is additive). Bottom line is that the antenna system is going to perform ALOT differrently depending on the frequency that it's receiving. Hence the odd analogy of the two cars. Think of the cars as the radiowaves being received, one into each antenna. As long as the speed (frequency) doesn't vary from what the cars can handle (antenna system tuned frequency) everything is just ducky. Once that changes due to the speed changing (frequency changing) things begin to go wrong.

Yeah, it was a bad analogy, but it made sense at the time.

If someone wahted to spend the money to try it, then they should. All I am saying is it may have other effects that they were not counting on.

 

[ohiodesperado]

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?"

You know, once I re-read this, I believe I have a better answer for you. That being that police cars don't typically ahve phased arrays on them, buut rather multiple radios that may be operating on a similar band.


This is more prevalant on the 400 Mhz band than on 150. In fact Motorola sells 3 different 400 Mhz banded antennas.406 to 420, 420 to 450 and 450 to 470 if you are talking about those small little steel whips with the ball on the toop that are NMO mount.
400 is typically a 5 Mhz split on the repeaters, but not always. There are wide split systems that are 12 Mhz apart and there is a good possibility that there is a receive antenna seperate of the transmit. The other possibility is that if it's a local city car, they may have a city radio and a county radio that are completely seperate but run on a similar band. State patrol cars in Ohio, before the APCO -25 system had low band, 150 400, 800 on some and even a GPS (1.5Ghz) antenna on them. They looked like a porcupine running down the road.

The idea of a phased array on a police car wouldn't make alot of sense because they would need to 'point' the car and the array towards the receive site in a fringe area and it would actually reduce coverage from the side in that fringe area.
Or at least that would be one possible explanation.

 

[Don_Burke]

The reason that a semi truck experiences the side null is that the signal coming from either side reaches the oppsite side 1/4 wave later at 27 Mhz (about 9 feet) I properly setup co-phasing harness is 1/2 wave electrically. So the signal gets the the center point out of phase of each other and attenuates the side signal. The signal that is coming from the front or back reaches the antennas ath the same time and not attenuation occurs.

This is so screwed up it is making my hair hurt.

 

[N_Jay]

I am not questioning this. I do agree, but what I am talking about is the effect is going to be more pronuouced in receive than in transmit.

Hu????

No, the effect is EXACTLY that same receive or transmit!!!!!


Different frequencies will make a difference.

 

[fmulder13]

Wow! I know I'm dealing with some people who know what they're doing. Let me clarify a few things. First, my original plan was to take two vhf-hi 5/8 wave antennas that were cut the same way and were identical down to the make and model, mount them with the same exact hole mounts, and run the exact same type and length of coax to a RadioShack t-connector which would be directly connected to my pro-2096. The non-repeater portables and the state police agency that I'm trying to hear better are both in the VHF-hi range, 154.xxxx and 155.xxxx. I also want to monitor other bands, but mostly the vhf is what i'm interested in. I thought I might have seen this scheme done on state police vehicles in my state, but someone suggested that the second antenna is connected to a second radio, which does indeed make sense. I thought phased arrays were fairly common on some patrol cars, and ohiodesparado I thank you for your advice on the subject. It looks like the general consensus is that it wouldn't be an experiment worthy of the extra dough and the risk that i'd have drilled two holes in my car for nothing. Looks like I'm going to go with just the one 5/8 cut to some compromise between the state and local guys, and go ahead and drill that hole! We'll see what happens...

 

[Don_Burke]

It looks like the general consensus is that it wouldn't be an experiment worthy of the extra dough and the risk that i'd have drilled two holes in my car for nothing. Looks like I'm going to go with just the one 5/8 cut to some compromise between the state and local guys, and go ahead and drill that hole! We'll see what happens...

I expect you will do okay. If you have trouble picking up the simplex traffic, see if you can borrow a two meter rig for a little while. (All of the two meter rigs I have owned have outperformed all of the scanners I have owned.) If that helps, try to scrounge up a commercial radio and get it programmed to just receive those 154.??? and 155.??? channels.

 

[ohiodesperado]

I expect you will do okay. If you have trouble picking up the simplex traffic, see if you can borrow a two meter rig for a little while. (All of the two meter rigs I have owned have outperformed all of the scanners I have owned.) If that helps, try to scrounge up a commercial radio and get it programmed to just receive those 154.??? and 155.??? channels.

Quoted for Truth! Commercial rigs will hear better and most will scan channels programmed into them. If you deside to get a ham license you can use it for ham as well.

As far as the comment about the extra holes and antennas on a car. I right now have 4 and I need to add two more as soon as I get the radio installed (800 Mhz Kenwood ) and I will be adding a second VHF antenna for the commercial VHF rig as soon as I find a Kenwood that is not priced out of reach like a TK-780 so it will match my 880.

I would sugest a Kenwood 880 for the 400 side of things.
I love mine. It's LTR ready and supports some silly 250 or so channels broken up into different banks. They refer to the banks as groups, because of the LTR trunking, but gives you tha ability to program different group entries as convential repeater and simplex channels. I would never advise you transmit on a public safety channel, but if a situation like a bad car wreck or something happened, you could summon help alot faster than even dialing 911.

 

[Raccon]

That is the problem; "he thinks".

That is the center-point of the whole discussion.

I figured that, so why comment on the 0.1dB issue when he didn't even claim that you said this?

If he "thinks" that he can find a satisfactory solution by taking shortcuts then it's fine by me, but feel free to differ.

 

[N_Jay]

I figured that, so why comment on the 0.1dB issue when he didn't even claim that you said this?

If he "thinks" that he can find a satisfactory solution by taking shortcuts then it's fine by me, but feel free to differ.

Only because he was stating it as "fact".

I hate to see others misinformed.

 

[prcguy]

What you are proposing is a huge waste of time and effort if your goal is to increase signal strength. Co-phasing is simply not used in the commercial/public safety sector and other posts about multiple antennas for multiple radios are correct. The only deviation from this is the 4 whip VHF arrays for Lojack, which is an active direction finding system and the early 800MHz systems that had diversity receivers and a second antenna. This is not co-phasing but a complete separate receiver that would supplement the main receiver to avoid some signal blockage and picket fencing. There are some really sick looking antennas from Diamond or Comet that claim to be 1/2 wave over 1/2 wave or 5/8 over 5/8 and are nearly 4ft tall. This would be about the best “practical” antenna to use for VHF, especially if mounted on the roof.
prcguy

Wow! I know I'm dealing with some people who know what they're doing. Let me clarify a few things. First, my original plan was to take two vhf-hi 5/8 wave antennas that were cut the same way and were identical down to the make and model, mount them with the same exact hole mounts, and run the exact same type and length of coax to a RadioShack t-connector which would be directly connected to my pro-2096. The non-repeater portables and the state police agency that I'm trying to hear better are both in the VHF-hi range, 154.xxxx and 155.xxxx. I also want to monitor other bands, but mostly the vhf is what i'm interested in. I thought I might have seen this scheme done on state police vehicles in my state, but someone suggested that the second antenna is connected to a second radio, which does indeed make sense. I thought phased arrays were fairly common on some patrol cars, and ohiodesparado I thank you for your advice on the subject. It looks like the general consensus is that it wouldn't be an experiment worthy of the extra dough and the risk that i'd have drilled two holes in my car for nothing. Looks like I'm going to go with just the one 5/8 cut to some compromise between the state and local guys, and go ahead and drill that hole! We'll see what happens...

 

[ve3oqcMexico]

Phasing antennas

This is somewhat late in posting,but here it goes.
Well,there seems to be a lot of misinformation here.Yes you can successfully phase two antennas together,remember that at Vhf the spacing is quite forgiving especially at vhf.I use two 1/4 waves on the trunk of my car for 6 meters (50 Mhz) NMO mounts with 6 feet of cable from each mount to my Yaesu FT-897D mounted in the trunk going to a power divider at the radio.Now for my situation the two 1/4 wave antennas are set to about 0.2 wavelengths at 6 meters which gives me directional ability from front to back and suppressed side lobes of a few dB,not much but it is what I was going for when running mobile because most of the propagation here is from north/south and this does quite well.If at all possible use trunklip mounting instead of mm´s.
Now you really don´t need a power divider for your particular set up just a good quality ¨T¨connector.I have used this configuration for some time and on different vehicles and am quite pleased and no you won´t be wasting your time,if direction mobile ability is what you are looking for then try it.There may be a compromise at some frequencies with larger spacing and at uhf the nulls will be sharper.Spacing elements on your car is somewhat similar to a two element mono-pole antenna,find the right spacing for all the bands you would like to monitor,try this and find a parking lot and drive around in circles while listening to the received signal.On some installations the nulls are similar to AM loop antennas,again it all depends on your experiments.

Good luck,hope this helps you.

 

[N_Jay]

Back to the OP's question.
As stated several times; Don't bother.
One antenna, as centered on the car as possible is best.

 

[ve3oqcMexico]

Phasing antennas

One part of his question was whether or not he could do this to improve his ability in finding transmitters when they are using a simplex frequency.The answer is yes, by phasing two antennas you do have the ability to ¨move around¨to find the general direction within 180 degrees.I have used phased systems on 50 Mhz for about 20 years with good results each time,and constantly have a good mobile signal on 6 meters compared to a singal antenna that I have used.
And in the area of 150 Mhz a 1/4 or greater spacing would bring in deeper side lobes and more of a figure 8 pattern.
On 27 Mhz (using phased systems) there would be no forward gain as most short verticals already operate with -2 to -5 dB gain to begin with,due to inherent ground losses coupling losses etc.There would however be an enhancement in received signal strength but nothing on transmit.
The military uses it,aircraft use it,Naval and commercial use it,and I have installed many phased arrays.
Get the picture?!

Experiment,experiment, I believe that you will find that by doing this you may find a common ground.