Base Should I stick it?

[JAF0]

If you look up at post 18, that is 3/8 wavelength radials to the ring, and the central vertical element was tuned for peak gain. It is longer than 3/4 wavelengths in length, but that should give an idea of such an antenna's performance.


The DB

Well I went back and read it again but I see current below the top 1/2 wave length that's not captured by the basket. If the entire antenna were 7/8 wave length and the basket 3/8 wavelength, wouldn't the ring be right at the bottom of the upper 1/2 wave of current instead of a little below it?

 

[Marconi]

Sorry to be late in my added response to this thread.

Maybe it is the matching system that I have added, but my results differ.

Both of these have an AGT of 1, are set the same height above the earth, are over the same earth, ect. The original model I used was created by ghz24, then modified by me, and in this case was set to the dimensions that HomerBB got his best results with this antenna design. The only difference between these models are one has horizontal radials and the other does not. With this result, you won't notice a difference.

DB, below are two model overlays I posted for my New V4K vs. Antenna Specialists version of the Sigma 4. Both models are set to the specs I have based on my real S4 antenna and the NV4K specs are as posted by Bob85 some time back on this forum. Early in this thread I posted my model of the Vector 4k with and without radials using the mount noted in Bob's specs. You are correct I placed the radials at the bottom of the V4K mount noted as 13.75" inches long and below the hub.

When you posted above that you placed your radials on the Vector at or close to the base of the hub, I had the thought this difference might make a noticeable difference, so I modified my radials as close to the hub as I could get. 1" inch will work with a slight difference to be noted, but I decided to make the mount 4" inches below the hub instead. Again, I noticed only a slight difference in the results...with no difference in gain/angle but a small difference in the match.

I read the whole thread again and saw where Bob mentioned Henry's published report on "The Avanti Sigma 4.

http://cb-antennas.com/?page_id=780

This gave me the idea that maybe the S4 and the NV4K, having different dimensions primarily in the cones radial length, might also account for the difference that Bob mentions regarding Henry's information on page 41, "Room for Improvement?"

So, I modified my models and posted the overlays below.

If my model overlays are close, and it is questionable for sure, then maybe Henry's results were accurate but only for the Sigma 4 with radials added.

My models do not include the gamma match, albeit the matches are fair and suggest the antennas are safe for radio operations. That said DB, I cannot add more to your ideas about the gamma match effects that you included in your models.

All my models show Average Gain results in Free Space no worse than 0.998 - 1.002.

You will notice in the overlays that the S4 with 3 horizontal 89" inch radials close to the hub shows the best gain of 5.58 dbi at 9* degrees TOA. The V4K without horizontal radials added is a close second with its gain of 5.44 dbi at 8* degree TOA. The angle difference maybe worth noting however.

I tuned the S4 horizontal radials I added to the best length for maximum gain, but I forgot to do the same on the NV4K. I will follow up if such a fix for the NV4K makes a notable difference.

I am aware that Eddie is getting a different result than I am, even if I put the radials lower down like he did, and I have come up with two possibilities as to why.

1) My model includes a gamma match, which may or may not have an effect. In the past I have shown that adding in a matching network can change the current flow on the antenna to some extent, so it isn't beyond reason that we are seeing some difference because of this.
2) The dimensions of our models are likely at least a little bit different. My model, for example, is built based on HomerBB's dimensions. I do not know what dimensions Eddie used, but if he used the stock Vector dimensions, they are different. It is very likely that the dimensions I used as a starting point are simply more stable to this addition than the dimensions Eddie used.

The DB

As you note DB, there are just too many difference in the dimensions to be sure about our trying to compare these results. I can only guess that maybe the added length of the cone elements is possibly making some difference.

I used a Sigma 4 with 3 x 90.5" inch elements in the cone and then added 3 x 89" inch horizontal radials 4" inches below the hub for my modified model of the S4.

I also added 4 x 108" inch horizontal radials 4" inches below the hub on my NV4K with 4 x 107" inch elements in the cone. I forgot to check the radial lengths for best gain on the Vector model however.

do you know why Henry's models show a different result for signal with radials than your model, you have the same trend but nothing like as much difference,

Well Bob, my Sigma 4 model with 3 x 89" inch horizontal radials added...shows the maximum gain for this group. My NV4K with 4 x 9' foot horizontal radials added came in last among the group. My S4 model with 3 horizontal radials added shows the best far field results. If this is close to accurate then maybe this is indicative of Henry's surface wave model results...and maybe DB's model of the Vector is less effected by adding horizontal radials like I think he has suggested.

The use of the (*) beside the models in the PDF file below is the active model. This shows the gain and angle results to the right of the page below the pattern.

I can't add any more ideas in response to your question Bob.

 

[Marconi]

My models do not include the gamma match, albeit the matches are fair and suggest the antennas are safe for radio operations. That said DB, I cannot add more to your ideas about the gamma match effects that you included in your models.

All my models show Average Gain results in Free Space no worse than 0.998 - 1.002.

Earlier in my post #32, I did not try an match the models and I noted the models showed fair matches with near perfect Average Gain results. IMO it likely would matter little if I got them to match. However, DB made a point that his models were all matched and also showed very good AG results. Thus I matched my two Sigma4 and two NV4K...both with and without horizontal radials added in my attempt to respond to JAF0 question about adding radials to his Vector...in light of the discussion.

I mentioned earlier that my models showed the Sigma4 responded nicely when adding radials, but my New Vector 4K just showed mediocre gain. My V4k model without radials showed better gain results and about matched the S4.

Since Henry's report came up in discussion on the Avanti Sigma 4, I decided to consider both designs per the dimensions I had available.

File 1. shows an overlay of the pattern for the 4 models in the order of maximum gain. The models are at 36' feet to the feed point and set with Ground Description set to medium (0.001, 5), or very poor: cities, industrial per Eznec software.

My model was set a 27.205 MHz. When I attached the mast to the antenna mount the model went a little capacitive...showing a reactance -5.757 ohms at the feed point. This made the radiator short and thus raised the resonant frequency to 27.30 MHz. I did not tune this out of the model. The model shows a bandwidth of 1.30 MHz at the feed point. When I tuned the reactance out of the model the BW did not change, but the antenna was resonant at 27.205 MHz as a result.

File 2. is a model of my Sigma 4 with my idea of a gamma match in Free Space. It shows the Average Gain results and all models show near perfect AG at or near = 1.

File 3. is a model of the Sigma 4 noted in File 2, however it is over Real Earth. It too has three horizontal radials mounted at the base of the 16.5" mounting bracket. I added the mast to the antenna, but it is isolated (ISO) 4" inches at the base of the mounting bracket.

File 4. is the same model as #3 above, but the antenna is not ISO from the mast. This model shows no indications of Common Mode Currents on the mast as does the other model that is ISO. The gain with the no ISO did drop a little however. The match changed very little.

To check if the length of the mounting bracket made a difference in the gain and/or match, I set the 3 horizontal radials 1.00" inch below the hub and the gain dropped from 5.44 dbi at 8* degrees to 4.84 dbi at 8* degrees. The SWR match with the horizontal radials set 16.5" inches below the hub dropped from 1.116 ohms to 1.147 ohms when set at 1" inch instead.

Thus, I think W8JI and Henry might arguably be correct in suggesting that radials will help the gain a little when added to the Sigma 4, but according to my models here...this does not seem to apply to the New Vector 4K with its larger radial cone. Only some real good real-world testing will prove one way or the other. That said, Henry reported on the Sigma4 and I'm not sure about the source of information given by W8JI on this design.

 

[Marconi]

i know w8ji said it needs radials, i will find out when i try it,

Bob I have a vague recollection of w8ji writing something about the claim you mentioned. My memory is he posted and showed an image or two as an updated part buried somewhere in an older article.

Do you have any clue as to where he said this.

I also recall w8ji posting on eHam in Booty Monster's home brew article on his Sigma 4 clone and he mentioned there, in general, the need for radials on all end fed 1/2 wave antennas.

 

[bob85]

i think it was in booty monsters thread on eham Ediie
http://www.eham.net/ehamforum/smf/index.php?topic=75921.0

 

[Marconi]

Thanks, I had a thought that I saw an article where w8ji posted an image of the Sigma4 design and he was writing about this one needing radials. I also recall it was about the same time that BM was posting on eham.

It surprised me that he would post a CB antenna on his Website, but he did it for the Imax and he did post on BM's thread on eHam.

Thanks,

 

[bob85]

Eddie

The only time i saw w8ji model a sigma style antenna is the j-pole article on his site ,
i only recall him saying the antenna would benefit from radials,
https://www.w8ji.com/end-fed_vertical.htm

Henry is not saying adding radials increases the gain of the sigma style antennas,
he's talking about radials increasing signal strength at the receiver 30km from the sigma with & without radials at various heights above ground.

 

[Marconi]

Bob, I see what you are talking about with w8ji's info in the link you posted.

Maybe that was what I remembered seeing and just forgot the details. However, I was thinking somewhere he showed us a model a S4 with horizontal radials added. I know Henry did on page #41 of his report that you posted in 2014.

If this is not the case, then were did the idea to add several horizontal radials to a S4/NV4K originate?

Thanks for the help.

 

[bob85]

I have seen w8ji add radials to a j-pole but only say that a sigma would benefit,

i don't know what made Henry add radials nor do i know how he came up with the graphs for signals at 30 kilometers from the transmitter, i am pretty sure its not extra gain,

i do recall Henry saying something about the open sleeve article not been the same as the sigma because the open sleeve has a ground-plane where the sigma does not,

i have been wondering for many years if radials would benefit a sigma style antenna,

if they work you have to weigh up the pros & cons,
adding 4 x 1/4wave radials to a vector significantly increases the real estate for birds to shit from, 30" > 17+ foot,

That's not the extra coverage im looking for.

 

[Marconi]

i don't know what made Henry add radials nor do i know how he came up with the graphs for signals at 30 kilometers from the transmitter, i am pretty sure its not extra gain,

I agree. My thinking about what Henry did in that case went in one ear and out the other. I suspect it was a feature available with Eznec Pro+.

I know you are right about his results not being gain...he clearly says it is signal strength being measured. I read somewhere that this measurement was a much smaller increment type measurement than typical gain. I once asked DB or Henry if they could tell me how this measurement related to gain. I don't recall the response, I just heard Henry caution DB about the use of the feature.

I read on the Internet comments in reference to surface wave measurements and our trying to compare gain results among several antennas under test. Tests where the results showed very small but detectable differences that were hard to impossible to determine without some more detailed way to measure. I could be wrong however.

I think I and others have suggested an idea many times before...when gain results were different yet very close...saying we probably couldn't tell the difference just using our radio. Maybe that is the time to dig out the old slide rule and maybe that is why Henry used the idea in his very comprehensive work.

There might be very high frequency technical reasons for folks wanting to make such detailed measurements, but I don't see much value in the HF range and for sure for CB hobbyists.

 

[The DB]

I once asked DB or Henry if they could tell me how this measurement related to gain.

As I have stated more than once before, surface wave measurments are not directly related to gain. Seriously, the only thing that is even close to similar between the two is they both have some kind of result, however, even the nature of the results you get from these two methods are different. To try and compare the two directly is a fallacy, its like measuring an orange with scale meant for feet...


The DB

 

[Marconi]

DB, like I told Bob, what I've heard about surface wave measurements went in one ear and out the other.

 

[Marconi]

DB, like I told Bob, what I've heard about surface wave measurements went in one ear and out the other.

DB, just to be clear... I did not mean my comment in a disrespectable way either.

 

[JAF0]

Well! Good to see more interest here, thank you Marconi. I thought my thread was long gone, bound for the archives
So what about adding an a99 radial kit? I just came across one in the garage I forgot I kept when I got rid of the a99
Even if it does nothing more than help keep common mode RF off the shield I'd consider that an improvement

 

[Marconi]

Well! Good to see more interest here, thank you Marconi. I thought my thread was long gone, bound for the archives
So what about adding an a99 radial kit? I just came across one in the garage I forgot I kept when I got rid of the a99
Even if it does nothing more than help keep common mode RF off the shield I'd consider that an improvement

Glad to see you back JAF0. Sometimes there are lulls in these discussions, but sooner or late they get active again. All you have to do is check in from time to time and respond to kick start the thread again.

I think the drift of my models of the S4 vs. New Vector 4K on adding horizontal radials suggest the NV4K does not respond as well in such cases. I think DB suggested the same, saying he did not see much difference adding radials to his Vector or a model he made.

Even so, I don't know for sure if I considered all that is necessary when I modeled your idea and since the delay in the discussion...I have gone on to other projects.

However, only real world testing this idea can say for sure, and even then the location and the installation can show different results in many cases. The only thing I can advise is keep your attention on the possible common mode currents problems that might come up with this antenna design, and try and keep the installation in the clear above and all around the install, it is reported by some to potentially have CMC issues.

If you decide to add horizontal radials...I would set the antenna up without them and get the antenna working right first...and then make your modifications, one step at a time. It is a lot of work but it might just pay off if you really what answers to your questions.

Over the years I have tested and compared my Sigma 4, but I've never had a NV4K to work with.

I will also add that I've watched closely on this and other forums...and I seldom see anyone with one of these type of antennas that gives any comprehensive performance reports that I thought reliable. Just saying it is the best antenna I ever owned or it stomped a hole in my Imax...is not reliable.

If you do this project, adding horizontal radials, please give us some good performance reports at points around your location, and if you do some comparisons to another antenna you have working...let us know how they compare in signals, noise, and maybe match.

Keep us posted on your progress and modifications.

JAF0, there is usually someone around that might be interested in what is said about these two antenna designs. I encourage you not to give up hope.