To 7/8 or NOT to 7/8, that is the equastion

[222DBFL]

Understood The DB. I'm still am learning and reading, and also learning by trial and error. I do appreciate all the input and it is duely noted sir. I am certain I can resolve my issue but there is a lot to be learned from just this install alone!! So the more input the better!!

 

[Galaxy 959]

Reading all this Coax length stuff. So if I upgrade to Times Microwave LMR 400 and the shortest the coax and can be is 50'. I go 492x.85/27.405 for 11 meter band? Which is 15.26. So to go by 1/2 wave lengths my coax needs to be 76.3'? Is that correct or am I way off?

 

[The DB]

Galaxy 959, what are you using that you need to be worried about coax length? If it is just a radio/amp and SWR meter, quit wasting your time and energy on this and get just enough coax to get from point A to point B, and a little extra for some wiggle room as that is all you will need. That, again, is the one and only correct length of coax to use. There is absolutely no benefit to operating a radio/amplifier through an electrical half wavelength multiple of coax.


The DB

 

[Galaxy 959]

Galaxy 959, what are you using that you need to be worried about coax length? If it is just a radio/amp and SWR meter, quit wasting your time and energy on this and get just enough coax to get from point A to point B, and a little extra for some wiggle room as that is all you will need. That, again, is the one and only correct length of coax to use. There is absolutely no benefit to operating a radio/amplifier through an electrical half wavelength multiple of coax.


The DB

I just see a lot of this coax length hype all over the net. I'm not using anything special. Cb radio with sideband hooked to a antron 99 right now. I didn't know if it made much of a difference or not. I'm still kinda new to this cb thing but learning.

 

[The DB]

There is really only one time that said length would be of use, and that requires a device which I doubt you, as someone who is "kinda new", has. Don't worry about it. As I said above, your radio/amplifier won't notice any difference, and for that matter neither will your SWR meter. If they do then you have other problems you need to deal with.

With many things in CB radio, something that has a minor effect, and in some cases only affects a very limited number of situations, gets blown out of proportion. This length of coax myth is but one of them. It comes from people who see differences with different lengths of coax, but don't understand why they see these differences, or the problems that actually cause them. They also notice that when such problems that they are unaware of exist, that some seemingly magical lengths of coax seem to make the problem go away, when in reality it only hides the problem, not fixes it. A hidden problem is still a problem.

There is a lot of this in the radio hobby. Unfortunately it is something that we all have to sift our way through at some point.


The DB

 

[Galaxy 959]

There is really only one time that said length would be of use, and that requires a device which I doubt you, as someone who is "kinda new", has. Don't worry about it. As I said above, your radio/amplifier won't notice any difference, and for that matter neither will your SWR meter. If they do then you have other problems you need to deal with.

With many things in CB radio, something that has a minor effect, and in some cases only affects a very limited number of situations, gets blown out of proportion. This length of coax myth is but one of them. It comes from people who see differences with different lengths of coax, but don't understand why they see these differences, or the problems that actually cause them. They also notice that when such problems that they are unaware of exist, that some seemingly magical lengths of coax ?seem to make the problem go away, when in reality it only hides the problem, not fixes it. A hidden problem is still a problem.

There is a lot of this in the radio hobby. Unfortunately it is something that we all have to sift our way through at some point.


The DB

So would lmr400 be a noticeable difference if I upgraded from my rg8u foam?50' length.

 

[Road Squawker]

So would lmr400 be a noticeable difference if I upgraded from my rg8u foam?50' length.

perhaps I missed it, is this a fixed antenna or a rotatable one?

you are not going to see any real performance difference between RG8/, or LMR-400.

RG8 and RG213 can be used in applications where the cable needs to be "flexed" (i.e. to go around a rotor) whereas LMR-400 has a solid aluminum (flashed with copper) center conductor and therefore will break in a VERY short period of time if used in an application where the cable is "flexed".

TIMES LMR 400 is made in several different versions. The plain (cheapest) version has a solid aluminum center conductor that is copper clad. Works great for all but an installation that needs constant flexing. (Like around a rotor).
TIMES LMR 400 "Ultra Flex" has a stranded copper center conductor, (And costs more).

The LMR type coax should last much longer than the RG8 type, but , other than that, for your application it is overkill.

 

[Needle Bender]

Sorry, been swamped, but here's an interesting thingaroo I just realized:

When I first rec'd my Gainmaster I tested it against the Imax on the same pole & using the same radio/coax, 60' of 9913 (84% VF) working out to 1.98 wavelengths - call it 2 even.
The Gainmaster destroyed the Imax by: S8 - Imax, S9+3dB Gainmaster.
That was at 40.5' (1 & 1/8 WL) above ground and fed right at 2 WL.

However, when compared at 54' (1.5WL above ground) and with 2.5 WL of 3/8" hardline the SAME Imax beat the SAME Gainmaster by a comfortable 1 S unit.

Again, at 41' at a friend's home, using 4.5 WL of LMR400 HIS Imax comfortably beat HIS Gainmaster by about an S unit.

Now, not a very scientific test at all, I know, but in both instances when fed at the X.5 WL, the Imax beats the GM, but when fed at the X.0 WL, the GM comfortably beat the Imax, at the same height at which a different Imax beat a different GM when fed at an X.5 WL length of coax.

- Maybe relevant, maybe not, but definitely one of those things that makes me go, "Hmmmmmm".

 

[Needle Bender]

Below are the same model overlays with various radiator lengths I did earlier in Free Space. This time I did them over Real Earth.

Here I compare the various length antenna radiators with no mast, with an isolated (ISO) mast, and with a mast directly connected to the antenna.

You will note the similar trends in the patterns, gain, and angle results that my previous Free Space models indicated. Click here; is a link to the Free Space models: http://www.worldwidedx.com/threads/...at-is-the-equastion.189729/page-3#post-529597

Again all of the models with shorter radiators show better patterns, and a bit better performance at low angles to the horizon, however notice the overlays with the mast directly connected to the antennas show less differences in gain and angle for all the various length models. This surprises me that the antenna models with mast attached directly to the antenna did not show as much difference in maximum gain or angle for my other Vector models reported in this thread with various lengths. However, these are just models and these findings need to be tested in a real world situation to be sure.

In my real world testing however...I don't think I was ever convinced with as much difference as others report...just using my radio. Click Real Earth models noted below.

Marconi What length mast did you program in on these plots?

 

[Marconi]

Marconi What length mast did you program in on these plots?

If you tell me the title of the model...maybe I can answer your question.

Typically I model over real Earth at 32' and 36' feet unless there is a specific height for a reason.

 

[Needle Bender]

If you tell me the title of the model...maybe I can answer your question.

Typically I model over real Earth at 32' and 36' feet unless there is a specific height for a reason.

Well, I'm wondering what length mast you tend to prefer when laying out your plots?
I'm looking at several of your plots in this thread and others.

My curiosity is based on wondering how the mast loads an antenna like the NV4K and how the pattern is affected if set with different mast lengths such as (edited from "with") 1/4, 1/2, 5/8, 3/4 & a full wave masts.

It would seem to be a good idea to completely RF isolate the mast on a (edited from no 'a') fiberglass rod & by using a current choke so the cone will load with ALL the supporting currents.
Seems to me that if the mast loads with any current it would be a continuation of the inverted current contained by the cone, causing perhaps a skewed pattern &/or dBs lost.

(ADDITIONAL EDIT)
OK, this is really frustrating me so I'm going to risk saying something.

It's a new year and I'm making some personal changes which should provide me with less frustration in my life (one of which is having my posts look like I'm figuring it out as I go or don't really know what the hell I'm thinking, - which is what it looks like to me when I see "EDITED") and the frustration lies in having to run full-speed and try to squeeze in all my corrections in typing, spelling, phrasing etc. before the 4 minute 59 second clock times out and then my post carries the irritating tag "EDITED".

I'd like it if that were changed to a reasonable amount of time, such as 20m.

In the future I'll simply be deleting my post and leaving the word "EDITED" where the post would've been.

Certain other forums don't provide any time for editing, if you edit at all it carries the "EDITED" tag.
- I don't frequent those forums.

I like this forum but would seriously enjoy enough time to make my posts as readable and well-phrased as possible and that simply isn't possible in a word document before posting because it always looks different once posted, and I'm far from perfect in typing, spellnig and phrasing so I NEED a bit of time to "kerrect amd purphekt" without feeling I'm being persecuted for taking the requisite time to do so.

And NO, I'm not in a bad mood due to having had too much New Years cheer last night. I had a coffee milkshake, no alcohol.
I'm just tired of feeling the pressure to "HURRY!!" when thinking I'm going to enjoy a few minutes of reading & posting on a forum related to one of my hobbies.

I've heard it said, "The squeaky wheel gets the grease!", but everyone knows the screeching wheel gets tossed out.
I hope I'm not being too 'screechy'.

Good morning & happy new year.

 

[Marconi]

I totally agree with every thing you are thinking from the (ADDITIONAL EDIT) on down, but I also suspect these forums were intended for short chats and casting comments.

I guess keeping these posts open for editing...must be some sort of burden on the staff, because sometimes I see the edit feature remaining open for quite a while, and other times the edit feature seems to shut down in just a few minutes.

In my thinking your other issue here is a lot more complicated. You raise some good points regarding the Earth ground, height or the actual length to ground, and how isolating or not can effect pattern and performance results in modeling and in the real world.

IMO these difference are generally small at 11 meters, but there is a valuable old saying..."every little bit helps...if you're not trying to fix something that ain't broke." I added a little bit to this old saying.

 

[Needle Bender]

I totally agree with every thing you are thinking from the (ADDITIONAL EDIT) on down, but I also suspect these forums were intended for short chats and casting comments.

I guess keeping these posts open for editing...must be some sort of burden on the staff, because sometimes I see the edit feature remaining open for quite a while, and other times the edit feature seems to shut down in just a few minutes.

In my thinking your other issue here is a lot more complicated. You raise some good points regarding the Earth ground, height or the actual length to ground, and how isolating or not can effect pattern and performance results in modeling and in the real world.

IMO these difference are generally small at 11 meters, but there is a valuable old saying..."every little bit helps...if you're not trying to fix something that ain't broke." I added a little bit to this old saying.

OK, to RE-re-clarify, my question points to the possibility of a non-isolated mast becoming part of the antenna/RF radiating surface and whether it does, and in doing so perhaps degrades performance.

Might be enlightening to offer a plot with an isolated NV4K as the reference then overlay the plots including those different mast lengths which I mentioned in my earlier post, all at, say, 45' to the antenna base, which I presume is a fairly typical installation height.

In case you have any doubts, I really enjoy your plots, Marconi.

 

[Marconi]

OK, to RE-re-clarify, my question points to the possibility of a non-isolated mast becoming part of the antenna/RF radiating surface and whether it does, and in doing so perhaps degrades performance.

NB, the first attachment below includes a NV4K with a non-isolated mast at 45' feet. I also made a model with a 4" inch isolated mast below the antenna mount (wire #1) for comparison.

I also attached a currents list of a partial print out for each model. Wire #179 is the top most segment for the mast, and it shows to be "OPEN". See the large black "X" as a marker in the antenna view. The X indicates a wire with an open end and thus it means the mast wire #61 is not connected at the top of the mast. Above this is a 4" isolation at the base of the antenna starting at wire #1.

As noted, this short list of the currents per segment is shown to demonstrate the very low current magnitudes on the mast for each antenna with a feed line 45' feet long. You can also see very little currents (red line) on the mast in the antenna view for both antennas. As a note I have this antenna set with 1 amp at the feed point and you can see the currents on the mast are just small fractions of am amp, and hardly worth noting.

I guess we could call this a lucky length, like W8JI does. IMO, he does this, because modeling currents is a complicated business, and he does not want to explain the ideas every time the subject comes up...and I don't either. So, he just refers to it as a lucky choice in length of feed line and I will too.

I also added an overlay of these two patterns, and here I see very little difference that matters in this situation. Just don't get the idea that you can place your antenna at 45' feet and see the same results. There is more to these currents...I suspect.

 

[Needle Bender]

NB, the first attachment below includes a NV4K with a non-isolated mast at 45' feet. I also made a model with a 4" inch isolated mast below the antenna mount (wire #1) for comparison.

I also attached a currents list of a partial print out for each model. Wire #179 is the top most segment for the mast, and it shows to be "OPEN". See the large black "X" as a marker in the antenna view. The X indicates a wire with an open end and thus it means the mast wire #61 is not connected at the top of the mast. Above this is a 4" isolation at the base of the antenna starting at wire #1.

As noted, this short list of the currents per segment is shown to demonstrate the very low current magnitudes on the mast for each antenna with a feed line 45' feet long. You can also see very little currents (red line) on the mast in the antenna view for both antennas. As a note I have this antenna set with 1 amp at the feed point and you can see the currents on the mast are just small fractions of am amp, and hardly worth noting.

I guess we could call this a lucky length, like W8JI does. IMO, he does this, because modeling currents is a complicated business, and he does not want to explain the ideas every time the subject comes up...and I don't either. So, he just refers to it as a lucky choice in length of feed line and I will too.

I also added an overlay of these two patterns, and here I see very little difference that matters in this situation. Just don't get the idea that you can place your antenna at 45' feet and see the same results. There is more to these currents...I suspect.

As always, thank you Marconi for your effort.

I'm wondering if masts of different lengths, (beneath the same 45' high NV4K) would change the amount of current in the mast in the non-isolated sim.
What if you told the sim that the 1/4 wave, 1/2 wave, 5/8 wave, 3/4 wave & full wave length mast lengths beneath it were PART OF THE ANTENNA? Would that possibly change it's view of the radiated mast current?