Cophasing any 50 ohm antennas(beating a dead horse again)!!!!

[bob85]

lol@CK

 

[Captain Kilowatt]

And the resulting pattern can be further refined by changing power to each antenna. It doesn't have to be split 50/50...

EXACTLY! Phase angles and power ratios do it all. Basically the phase angles determine the rough shape of the pattern while the power ratios determine the size or depth of the lobes and nulls.

Jeeze....I just had a flashback to CKAD. 110 degree towers spaced 180 degrees apart. North tower leading by 55 degrees as referenced to the center tower, South tower lagging by 55 degrees and a power ratio of 1:2:1
Not a hugely complicated system but it was touchy as hell to get the power ratios and phase angles to line up all at the same time. :headbang

 

[Needle Bender]

First I just want to say that it is 100% possible to achieve good gain, up to about 4 dB when using 1/8 wave spacing but the pattern is NOT omnidirectional.

Most everywhere I read on CB forums people say it is impossible to achieve gain at less than 1/4 wavelength spacing and trying to do so is fruitless. They are so wrong and the reason they are wrong is they do not understand phase angles. They assume that both antennas are fed in phase.

Let's take two vertical antennas that are identical and mount them 1/8 wavelength apart on a vehicle. Lets assume they are on either side of the vehicle. With both antennas fed in phase the gain is a miniscule 0.3 dB and the pattern is almost completely omnidirectional with a slight flattening toward the sides and a slight bulge out the front and rear. Now if we do something radical like feed the antennas with unequal lengths of coax we end up changing the phase angle between the antennas and this is where we start to see big differences in patterns and gains. If we feed one antenna with an extra half wavelength of cable then the antennas are 180 degrees out of phase and the pattern becomes like a figure eight with the main lobes out the sides and the nulls towards the front and rear. The gain is near 3.8 dB. If we use an extra 3/8 wavelength of cable the gain is 4.2 dB with the pattern unidirectional towards one side, the side that has the extra cable. This can all be seen and explained better on page 8-6 of the Radio Amateurs Antenna Book 17'th edition if anyone has one. Omnidirectional gain can only be achieved by vertical stacking of antennas HOWEVER gain can be developed with as little as 1/8 wave spacing if one can live with the resulting pattern.

I just wanted to say this because I am tired of hearing that YOU CANNOT GET GAIN FROM LESS THAN 1/4 WAVE SPACING. You can. You just need to know what you are doing and be aware of what the end result will actually be.

Good info!

So, setting up a little metal project box with a multi-position switch, a few relays and a few switchable coax lengths, you could make the vehicle's antenna system somewhat directional, which I can see being helpful at times when interference is in the wrong direction compared to your QSO station, or when gain (1-1.5 S-units on most meters) is required due to the limitations of a mobile antenna system.

 

[Captain Kilowatt]

Yeah that would work. You would want lengths of 1/4, 3/8, and 1/2 wavelengths of cable (90, 135, and 180 degrees respectively) and be able to insert them into either side of the system to make the most of the capabilities. The greatest benefit comes from the deep nulls to reject interference rather than the small peaks of increased signal strength.

 

[jazzsinger]

Rarely do i agree with Jazz when he goes off on a tirade but this time I have to agree with everything he has said.

Oh Lord Jesus it hurt to say that.

I'm deeply moved Ck,lol, but it pains me to know your hurting, a bit of advice from an old friend that feels your pain:

 

[Needle Bender]

Yeah that would work. You would want lengths of 1/4, 3/8, and 1/2 wavelengths of cable (90, 135, and 180 degrees respectively) and be able to insert them into either side of the system to make the most of the capabilities. The greatest benefit comes from the deep nulls to reject interference rather than the small peaks of increased signal strength.

Back in the '90s When I ran two 102" spaced a little over 1/8 wave apart, one on each side of the truck, I used enough extra length of 50Ω coax (only to one) to phase them 90° as in 1/4 wave spacing front to rear, and in doing so, removed the picket fencing effect when heading toward or away from the station.

Though it didn't offer any noticeable gain nor loss in any direction, it did help stabilize signals away from rapid fluttering & fading, which I had experienced earlier with only one antenna in the center of the cab.

 

[bob85]

remember whenever the two antennas are not the same impedance with zero reactance the phase angles shift, voltage will lead or lag current depending on the kind of reactance which throws your phasing line lengths off,

its what sets smart keydown guys apart from the also-ran's.

 

[jazzsinger]

Yeah that would work. You would want lengths of 1/4, 3/8, and 1/2 wavelengths of cable (90, 135, and 180 degrees respectively) and be able to insert them into either side of the system to make the most of the capabilities. The greatest benefit comes from the deep nulls to reject interference rather than the small peaks of increased signal strength.

I feel indebted so must repay the compliment Ckn just like so many people focus on cable loss figures and totally ignore shielding and jacketing/weatherproofing,the most important qualities,not much point having a good signal if ye canny hear shit for noise pickup or it falls tae fuck after a few months up.

as you rightly say far too many are hung up on marginal forward gains overlooking the obvious advantage of 15,20,25,30 db designs offering reducing crap,sometimes willing to give up double figure side or back rejection figures to gain less than 1db forward gain no-one will notice,its crazy,give me a 5.4db forward gain beam with 30db rear rejection anyday over a 6.5db forward gain beam with 15db rear rejection anyday.

There's so much bullshit out there its scary.in an age where so many are willing to share knowledge like never before and most answers only one google click away it puzzles me how this crap still propagates better than any rf signal ever did.

That's my ultimate goal in life, to make an rf signal out propagate a bullshit newsflash,

I have a dream.M.L.K. (Speech made on my sons birthday ironically) but still as relevent today.

 

[Grim Reaper]

you can state the arrl hand book i like that book,but its written by ham operarators alot of then in fact geniuses but when the nu tronics corperation,antenna specailist and the beam antennas manufactures went to get antennas designed and then state gains,they didnt reort to the book,they hired engineers who were far more trained than the books authors and the lot of cb forums all put together,that document came from antenna specailists,its dated 1983 unless the law of nature changed.all their info came from their engineers and we can debate this for 5000 yrs and you can say it divides all day.i wont argue the division,im stating that there is enough loss in a single antenna that when dbl it get a 3 db gain,and kilowatt look at the doc close you get a near 36o close enough it helps a mobile talk all dirctions better,and aas far as off setting and talking better?listen to a semi going away from you,ground on and this is mobiles of all kinds affects the radiation pattern of atennas,and if i move so i have more ground to any direction i gain that direction over others,but my effenicy is increased so much with duals, i can hear and out talk singles.ask youir truckers on here,real world,do you hear and talk better duals or singles?any and all dirctions?now if left mirror mount,ex here.you should talk forward equally if right mirror was used instead,now what happened when you went duals?

 

[The DB]

you can state the arrl hand book i like that book,but its written by ham operarators alot of then in fact geniuses but when the nu tronics corperation,antenna specailist and the beam antennas manufactures went to get antennas designed and then state gains,they didnt reort to the book,they hired engineers who were far more trained than the books authors and the lot of cb forums all put together,that document came from antenna specailists,its dated 1983 unless the law of nature changed.

I am still waiting for you to post a link to a full article that you are referring to. I am also still waiting on the full text of your first attachment in your first post (not just a single page), the documentation of the military's findings, and so on. Making references doesn't do anyone any good without the complete articles/papers to put them in context. As of yet you seem to be using them to prop up your rather extreme statements, however, I have yet to see them. Some people will back off at the mere mention of such sources, I am not one of them, and when such a source is mentioned I want to see what you are referring to for myself. The lack of producing or quoting those sources in full context does not help your argument with me (and you will fine many others on this site that feel the same).

all their info came from their engineers and we can debate this for 5000 yrs and you can say it divides all day.i wont argue the division,im stating that there is enough loss in a single antenna that when dbl it get a 3 db gain,

Just one problem with this is that with very rare exception, when you add a second antenna losses increase, not decrease. For example, on a car you have what is already a very inefficient setup at least partially due to the inadequate ground plane the vehicle body provides. You are suggesting that using that same inefficient ground plane for two antennas instead of one makes the whole system more efficient? While adding a second antenna may help tuning in *some* cases (when your limited to an SWR meter anyway), logically speaking, if the ground plane it isn't large enough to make one antenna efficient, what makes you think the same ground plane would be any better when it is being shared between two separate antennas?

and kilowatt look at the doc close you get a near 36o close enough it helps a mobile talk all dirctions better,and aas far as off setting and talking better?listen to a semi going away from you,ground on and this is mobiles of all kinds affects the radiation pattern of atennas,and if i move so i have more ground to any direction i gain that direction over others,but my effenicy is increased so much with duals, i can hear and out talk singles.ask youir truckers on here,real world,do you hear and talk better duals or singles?any and all dirctions?now if left mirror mount,ex here.you should talk forward equally if right mirror was used instead,now what happened when you went duals?

Grim Reaper, I think you are making two misconceptions here.

1) Duel antennas typically do ***NOT*** increase efficiency. This is especially true when mounted on any vehicle that does not present a large enough ground plane to make one antenna efficient to begin with, much less two. Actually, the best thing you can do to increase efficiency in a cophased setup is have separate ground planes for each antenna, good luck with that on a vehicle...

2) Beam and Omni antennas have very different properties when cophased. All of the evidence based on beam antenna research piled up in the world doesn't mean squat when you take two omni-directional antennas and cophase them. You are correct in one aspect, the radiation pattern between two omni-directional antennas at 1/8 wavelength apart is near circular, but the gain is NOT anywhere close to 3 dB as the first attachment in your first post in this thread mistakenly claims.

A little tidbit or two you may find interesting, there are broadcast engineers that post on this forum, and one of them may well be posting in this very thread (nope, its not me)...

Also, many broadcast engineers that as you put it "they hired engineers who were far more trained than the books authors and the lot of cb forums all put together". Many of these engineers actually refer to the ARRL Antenna Books as a reference...


The DB

 

[jazzsinger]

you can state the arrl hand book i like that book,but its written by ham operarators alot of then in fact geniuses but when the nu tronics corperation,antenna specailist and the beam antennas manufactures went to get antennas designed and then state gains,they didnt reort to the book,they hired engineers who were far more trained than the books authors and the lot of cb forums all put together,that document came from antenna specailists,its dated 1983 unless the law of nature changed.all their info came from their engineers and we can debate this for 5000 yrs and you can say it divides all day.i wont argue the division,im stating that there is enough loss in a single antenna that when dbl it get a 3 db gain,and kilowatt look at the doc close you get a near 36o close enough it helps a mobile talk all dirctions better,and aas far as off setting and talking better?listen to a semi going away from you,ground on and this is mobiles of all kinds affects the radiation pattern of atennas,and if i move so i have more ground to any direction i gain that direction over others,but my effenicy is increased so much with duals, i can hear and out talk singles.ask youir truckers on here,real world,do you hear and talk better duals or singles?any and all dirctions?now if left mirror mount,ex here.you should talk forward equally if right mirror was used instead,now what happened when you went duals?

Yep, we all know antenna builders only tell the truth,like antron/solarcon's 9.9dbi gain,certain ones who achieve audio gain etc etc, firesticks advice page is a good laugh too,having owned antenna specialist's antennas,yeah they were good but far from the best and if I recall most of their claimed gain figures were bullshit,

sirio a huge antenna building company with more money invested in proper test gear, military standard modelling software and an anechoic chamber (look that one up on google as I doubt you'll know what it is or what its for) were known for telling porkies about gain figures too, and only relented the practice recently when taken to task by those dumbass hams/cb'ers you refer too.

If you don't believe me ask Shockwave who is one of their main dealers in your country with access to antenna information you and I could only dream of,

others have been laughed off this forum for their outrageous claims.
Yet you want us all to believe in a couple of papers/documents you've failed to provide and obviously misinterpreted, as the DB has just hinted to you there is broadcast engineers on here disputing your claims who have years of experience,yet you mock them in favour of ones you misinterpreted, yet these guys give it to you straight as they have NO PROFIT to gain here.

Sure the ARRL books might not be 100% correct all the time,but then I've never read ANY book that was.

Even in perfect situations which don't happen very often in the REAL world if anything the gains you claim would be very very difficult if not impossible to achieve.

You really need to work on paragraphs and punctuation to be taken seriously here,one long drawn out droll, will bore 95% of guys on here before they read what your trying to say.

 

[Shockwave]

Antenna Specialist did make some decent antennas. Several of the better antennas that made a name for them were actually designs they bought from Avanti when they closed. Antenna Specialist also have no reputation for being honest in marketing or gain figures.

Need proof? I purchased a Polecat antenna from them in the 1980's and the ad can still be found online. It's an end fed half wave that claimed a 6 db improvement!!! 6 db over what I ask? In actuality, any end fed 1/2 wave will have less than 0 db gain over the dipole reference since the end fed has extra loss in the matching network. In this case they stretched the gain figure by more than 6 db. Almost as bad as Solarcon.

 

[Marconi]

Henry sent me this mobile model. I changed it into three mobile models. A whip on the roof, cophased on the bumper, and cophased on the tail gate. The patterns are included as an overlay to show how these models suggest the patterns, gain and angle might look. The two cophase models include an Eznec virtual (V5) 75 ohm cophase harness.

I can't say how accurate they are for details, but all three configurations are on the same mobile model.

View attachment Mobile model.pdf

If we wish to be nit-picking with the gain and angle, both the cophase setups show a little advantage in gain and angle with the tailgate high model looking to be the best option. However, I don't think we could tell the difference just using our radio...at least in the forward direction.

 

[Grim Reaper]

I stated it openly when i posted this,my meds affected my thinking processes hard,thanks for the corrections about db gains it is 2x5 not 5x5 and several others that imputted on this posting,thank you,you helped alot of other folks get a clear idea of what actually goes on, you used and posted facts,instead of what 75% of what most so called tech shops or other ham and cb'ers do,just spout out this dont work,the whole point in my posting this to start with was to start and end up exactly with whats here,verifible information t benifit otherts,God Bless all Ken