home brewing a gain master ???

[Needle Bender]

What's going on? If you need advice as to what to do, then tell us what you have in mind to do, so we won't just be just guessing in the dark. Asking for advice on your plan of attack around here can be risky business, and in particular if you're going to give us your final results beyond all doubt for how the Sigma4 works.

NB, I have no idea what you're about to do here, and I don't intended to suggest you expand your work unnecessarily. If it was me, and based on the limited reports that Bob85 and maybe others have given us...regarding steering the maximum angle of radiation by tuning, and that the Vector will only produce maximum results, at a distance, if tuned like Bob did his and made it longer, I would do the following.

A simple approach, might be to build a setup as close to a stock antenna as possible...just like what the manual suggests. I would suggest using a New Vector 4000, since that one is available and it has some instructions on setup.


I only thought you were just going to prove to us, beyond all doubt, that the Vector/Sigma4 didn't radiate from the bottom 1/4 wave cone element?


For me and to do that, it don't matter which antenna you use, as long as it is similar.

Well, I just didn't want to leave the door open for controversy based upon my not using the specific exact correct configuration of the on-going evolution of the Vector-Sigma4 style antenna, but I agree, it should perform as close as can be expected to any or all extension/size/tuning mods since they are all based upon the same basic basket design.

A family member has recently passed away here and the cost of burial has fallen upon me so I'm not sure if I'll be affording a new Vector anytime soon, but if I can beg/borrow one from a local friend who has one I might have this video finished sooner than I imagine and yes, I believe it will conclusively show exactly where RF is being radiated from the Vector.

But I won't put it past those best at word-smithing to reinterpret my findings in some way to make it seem as if black is white.
We'll see.

 

[northern35s]

Shockwave, I sure wished you had some visual evidence for what you're suggesting here. I can't argue with your words, and frankly -------------

---------- I could be wrong in how I perceive these current phase matters, and thus continue down a path with no logic, but one day I will get the help I request.

Sigma4 vs. .75 wave with slanted-up radials and no hoop. - YouTube

Interesting video, thanks for sharing your findings, that goes some way to explain what is going on with the Sigma 4, now all we need to find out is why the hoop has the effect it does op:

 

[Marconi]

Well, I just didn't want to leave the door open for controversy based upon my not using the specific exact correct configuration of the on-going evolution of the Vector-Sigma4 style antenna, but I agree, it should perform as close as can be expected to any or all extension/size/tuning mods since they are all based upon the same basic basket design.

A family member has recently passed away here and the cost of burial has fallen upon me so I'm not sure if I'll be affording a new Vector anytime soon, but if I can beg/borrow one from a local friend who has one I might have this video finished sooner than I imagine and yes, I believe it will conclusively show exactly where RF is being radiated from the Vector.

But I won't put it past those best at word-smithing to reinterpret my findings in some way to make it seem as if black is white.
We'll see.

NB, you can bet your "sweet bippy," what you predict might happen will happen, and you'll hear claims "out of whole sackcloth" with nothing to support any real work...even if you video everything.

I agree with you that a New Vector 4000 would likely be the best choice to start, but under the circumstances you have, any of the models should work as well as the next to prove your point. I think if you go further into trying to duplicate Bob85's finding, you will likely have to be using an Old Vector 4000 to get past the egnima for that one.

I base my idea for a choice simply on what I think is probably true of this model comparing my experience building the Sirio New Top One. In my opinion, these kits are unique, in that if you follow Sirio's instructions to a "T", you probably can't go wrong getting it to work fine, right out of the box...if it's well into the clear. This one is somewhat similar in the kit design and elements...which I find assemble to be sort of like "plug and play," with minimal dimensions to consider.

Just get it right, get it tight, and go:

"I DON'T THINK ONE CAN HARDLY GO WRONG FOLLOWING THE INSTRUCTIONS."​

 

[Marconi]

Interesting video, thanks for sharing your findings, that goes some way to explain what is going on with the Sigma 4, now all we need to find out is why the hoop has the effect it does op:

In looking back at the video 35, it could have been better and I should have done a couple of other comparison efforts between the two antennas.

Regarding my idea for what might be going on with the Sigma4/Vector.

Personally, I think the hoop is creating a high impedance voltage field that is sort of like the phasing stub in the BH 5/8 collinear I posted below, but it is not as complete in its function.

Thus we don't see the full affects of phasing for what a true collinear design can perform. This may be why Cebik told Bob, that the Sigma4 design has an "non-apparent collinear affect" going on, which is probably a very good description. That said, however, I'm sure to get objections to such an idea regarding what Cebik may have meant.

As an example to consider: check out the currents log for the Big Hair collinear 5/8 wave vertical below. Compared to those results to the Sigma4 you can see similarities. The current distribution on the Sigma4 appears to work as a collinear, but IMO it probably isn't quite as effective at doing the work, thus we just don't see the gain noted with the Big Hair collinear at a similar height. BTW, I have the phase feature turned on in the first model, and it is turned off in the second model. Check out the differences.

View attachment Collinear .625 w vertical 36'.pdf

 

[bob85]

Hi Bob, I know you're a proponent of the Vector 4000 and have read your comments about the same before now, I'd like to get my head around why it works as you, and Marconi, say it does

hello 35s, its good to see you on here,

have a look at what Cebik says about wider spaced j-poles

interesting note on relative phase with changes to element length, note what he says about radiation angle when the upper 1/2wave is extended, the arrl says the same thing about the open sleeve antenna,

http://www.cebik.com/content/a10/vhf/jp3.html.

all 4 parts are worth reading,


another antenna worth a look at is the skeleton sleeve fed monopole
[FONT=Arial, Helvetica, sans-serif]Antenna Projects and Notes
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[Marconi]

Marconi, ......................................

Your Sigma model without the loop behaved differently because you didn't extend the radials to compensate for the loss in electrical length once the loop was removed. Extend them some and the antenna will perform more like the loop but the pattern is less even and the mechanical strength is reduced.

Shockwave, you were right in you comment above. When I did the model project to test your idea, I built a new model with the radials slanted up, instead of removing the hoop from the Sigma4 model and comparing results. I also mistakenly made the radials only 98" long. I also found the radial angles were notably wider than the original S4 and all of the affected the phase and pattern badly.

I redid the original project this morning, and below are the results I should have posted. So, like you said, when I extended the radials out to about 106" from 90.5" for the stock S4, the model returned to a similar pattern as you note above. The current phase also returned to normal similar to the original S4 model. The phase issue, however, might have been partly due to the fact the radial spacing was notable wider for the model I built earlier, all mistakes.

Hopefully the following examples better represent more better what maybe going on in the bottom of the S4. With that said, I don't think I can still claim the hoop is somehow creating a high impedance field a 1/4 up the 3/4 wave radiator that justifies some collinear affect...like I earlier had in mind, albeit the tips of the radials should also show high impedance and maybe produce a less robust high impedance field.

Somehow these radials alone still mitigate all the bad nature of a 3/4 wavelength radiator with horizontal radials, and in addition produce a RF wave-front at broad and great working angles for CB, and with minimal high angle lobes, and nulls that only waste power generated into the sky.

View attachment Re-do of the Sigma4 with_without hoop.pdf

I forgot to scan the antenna view for the .75 wave with 105" radials, but the pattern is there.

 

[northern35s]

hello 35s, its good to see you on here,

have a look at what Cebik says about wider spaced j-poles

interesting note on relative phase with changes to element length, note what he says about radiation angle when the upper 1/2wave is extended, the arrl says the same thing about the open sleeve antenna,

http://www.cebik.com/content/a10/vhf/jp3.html.

all 4 parts are worth reading,


another antenna worth a look at is the skeleton sleeve fed monopole
[FONT=Arial, Helvetica, sans-serif]Antenna Projects and Notes
[/FONT]

From the second linked article I found the following comment of interest

However, the J-Pole does not produce a true omni-directional pattern due to radiation from the 1/4WL stub

I can see where the 'gain' comes from in the NEC plots, but question whether the same would be the case for the SSFM, one other question is why the Sirio/Vector is gamma matched, would there not be a 50ohm point between basket and and the main radiator?

It's certainly been interesting reading Marconi's findings with regards to the Vector and his up turned ground plane model, and the Cebik investigation into non standard J-Poles, I think I might wait until I'm on nightshift at work to take it all in and make sense of it (assuming I get a quiet shift ) too many distractions at home, and when I do get time to myself I'm too busy DXing

Thanks for your time chaps

 

[PhilipB]

very interesting from your article above philip

"If the radiation pattern of a vertical monopole over a perfectly conducting ground is studied, at a little over λ/2, the main lobe divides. This point is often taken as 5/8λ (0.625λ), but it is just a little less. So, in practice, a radiator of 0.6λ is quite sufficient."

From the measurements on the pic/plans you posted, i came up with a total length of 22.31 feet which ends up being .62 wl.

best of luck, work has me tied up pretty good and I will be on the road starting tomorrow evening until next week,,,but I will check in today and tomorrow before leaving.

Hi Gamegetter, on my quest to find out if it is possible to homebrew a cheaper low power version of the GM I have been directed to this similar antenna build link, it is a very interesting read and has answered some of my questions regarding the bandwith and the capacitor.
Hope you enjoy it.
http://www.antennex.com/preview/Sep09/the_x-pole.pdf

Phil

 

[PhilipB]

Hello again, I got so fed up trying to homebrew a GM and not getting it right (or anywhere near) that I have just purchased one, it is up on the short test pole in the garden at the moment but even down low it is working quite well, swr plots are spot on and it even performs reasonably on 15m with the little MFJ tuner hearing and being heard by stations that cant be heard on my 10m fishing pole vertical wire with unun and CP, after having a close look at the internals of the GM and taking measurments I noticed that the plans given to me are not quite correct, the top element wire (heavy stranded that looks like 15 to 20A rated wire) runs all the way down to the base of the coax capacitor within the heatshrink thus needing to be 10cm longer than the plans as that is the length of the coax capacitor, the red coax below the stub match is 1.72m and 1.50m above the stub match, stub match of the mysterious coax is 62cm and the coil/balun is 16 turns on a 2 and half inch former.

I have to say it seems to be very flimsy and springy in the light breeze we have here in the NE UK at the moment so I hope that they do take the big winds that they are reported to have survived, this is compared to my 10m roach pole antenna and my old A99.
Hope this information helps anybody trying to build one (and good luck if you are!)


Phil
M6MRP
26CT867

 

[PsiDOC]

Hi Guys.
I dunno if this is any use to anyone. Finished construction of a home brew Gainmaster yesterday. It's quite a straightforward antenna to build to be honest. Hardest thing to find was the matching stub connection point. Although I found this using the test, adjust and repeat method. The difficult part of the antenna is how to derive the matching stub connection point. This is now clear and is included in the thread linked in the next paragraph. Also may I add it was nowhere near where I posted earlier and I do apologise for that blatant error.

I have started a thread on transmission1.co.uk about it that includes pictures, construction details, the theory of the antenna and a little explaination about the matching stub connection point and how to use different coax cables and how they affect the matching stub connection point.

73.

PsiDOC

 

[Shockwave]

If you're going to homebrew a GainMaster, don't use RG-58 for the tuning stub. Shorted tuning stubs are made from silver plated Teflon insulated coax for a reason. Low loss. It's not the same line of thinking that just a couple feet can't have significant loss. Because it's a shorted stub, there are higher than normal currents on this cable and the loss of RG-58 will impact performance.

 

[PsiDOC]

Shockwave: Thanks for that gem if info. At the moment i am indeed using RG58 for the stub. I'll get a bit of RG303 and swap it. Be interesting to see the comparison.

Psi

 

[Marconi]

Shockwave: Thanks for that gem if info. At the moment i am indeed using RG58 for the stub. I'll get a bit of RG303 and swap it. Be interesting to see the comparison.

Psi

PsiDOC, I think you were trying to be very precise in duplicating your homebrew, right? Were you really able to use the dimensions you requested on the forum, to build this project?

Before you modified your homebrew using Shockwaves stub coax idea, do you think the matching results, resonance, and bandwidth compared similarly to the published Gain Master results?

My VA1 analyzer bandwidth using the feed line shows to be 5.0+ mhz wide. Do you see an SWR bump in your bandwidth curve between 27.5 and 28 mhz?

Have you recorded any contact results to compare if and when you modify the stub?

I notice you have your antenna low, do you sense any problems with the building obstructions around your install? Your other antenna looks to be mounted above local obstructions by a little bit.

Is the wire inside or attached to the outside in the images we see?

When you get this homebrew all setup and checked out...will you be able to mount it higher like your other antenna?

I own a GM, and I'm really impressed with its nice features, lack of any TVI issues with my install at my location, and a very wide bandwidth while maintaining very good performance.

How is your choke design working out for you with the antenna set so low?

Overall performance is pretty much on par and maybe a little better, if I compare it to my other CB vertical antennas at or near the same current maximum, and for me that is not unexpected in my experience. However, the GM does show some superiority when installed and compared with these antennas at the same feed point height. IMO this is due to the GM being very tall in addition to the way it uses the full 5/8 wave radiator...working all the radiator in phase.

In my checking of my bandwidth curve on my GM it show a sharp rise at both ends of the <2.0:1 curve, but may be right it may be a little sharper at the high frequency end.

Welcome to the forum. Be sure and keep us posted on you stub modification.

 

[PsiDOC]

Hi Marconi. If you don't mind I'll take each question one at a time and reply below it. Any more questions please do fire away and I'll do my best to answer them

PsiDOC, I think you were trying to be very precise in duplicating your homebrew, right? Were you really able to use the dimensions you requested on the forum, to build this project?

Yes I built the antenna initially as per the dimensions off the forum. However before I put a matching stub anywhere near the antenna I put it up on the test pole and checked it was exhibiting the expected impedance of a 5/8 wave antenna which as we both know is about 200 ohms. At 28.0 mhz it was 180+84J which works out at about 203 ohms.
So with that as a base point I went about the unknown factor of finding the correct point to attach the matching stub. I guestimated it to be closer to the centre as the original uses a foam dielectic with a higher VF so I made the coax choke with an extra 6ft tail to the pl259 connector. That way when I was chasing the matching stub point up the antenna, to maintain the correct length I simply rolled coax off the top of the choke and added it to the bottom from the tail as I shortened the top coax section.
Only when the matching point was found did I tweak anything else. You will notice I have the bottom section 10cm longer than the initial dimensions I started with. This was done to hit the 1:1 VSWR

Before you modified your homebrew using Shockwaves stub coax idea, do you think the matching results, resonance, and bandwidth compared similarly to the published Gain Master results?

I haven't actually got any teflon dielectric coax here to try as of yet, will see what's about in work tomorrow and failing that will order some. I will however post the results.

My VA1 analyzer bandwidth using the feed line shows to be 5.0+ mhz wide. Do you see an SWR bump in your bandwidth curve between 27.5 and 28 mhz?

I am seeing 1.9:1 at 25.5 mhz and 1.9:1 at 30 mhz. That's 4.5 Mhz bandwidth.
Actually here's the results on the meter at 0.5 mhz intervals at 100 watts into the antenna:
25.5: 1.9:1
26.0: 1.3:1
26.5: 1:1
27.0: 1.1:1
27.5: 1.4:1
28.0: 1.4:1
28.5: 1.1:1
29.0: 1:1
29.5: 1.4:1
30.0: 1.9:1
As you can see I am getting the bump in the middle at 27.5 & 28. Interestingly I didn't see this at the feed point wiht the MFJ analyser as I was watching for it as per the original swr curve from the manufacturer.

Have you recorded any contact results to compare if and when you modify the stub?

I have my logs here however on the day when I change the stub it'll be better to do before and after tests. Changing the stub will take 20 mins or so.

I notice you have your antenna low, do you sense any problems with the building obstructions around your install? Your other antenna looks to be mounted above local obstructions by a little bit.

Sadly I live close to the bottom of a big hill with the garden running west up the hill also the hill climbs to the south as well along with the row of houses in my street.. Hence why where the antenna is mounted is about 10ft up from the house on the garden level. The hill carries on for about 300ft or so upwards at an approx 8 degree angle. So local obstructions are a row of houses raising upwards to the south and hill to the west.

Is the wire inside or attached to the outside in the images we see?

Outside. Weatherproofed with heat shrink and silicone grease.

When you get this homebrew all setup and checked out...will you be able to mount it higher like your other antenna?

Already on the case. Have procured a 6m aluminium pole today.

I own a GM, and I'm really impressed with its nice features, lack of any TVI issues with my install at my location, and a very wide bandwidth while maintaining very good performance.

I must admit I like it's simplicity. With no tuning coils to be mucking about with and made out of coax and wire it can be made light weight and portable. I have made 1/2 wave sleeve dipoles before, however never a 5/8 that needed a matching circuit. Also having read about widebanding with a capacitor I had to have a go at building one to understand how it ticks.

How is your choke design working out for you with the antenna set so low?

100 watts into the antenna and zero common mode on the feedline. There's many and lengthy arguments about what dictates a good coax choke so I won't even enter into this one. It works and works well.

Overall performance is pretty much on par and maybe a little better, if I compare it to my other CB vertical antennas at or near the same current maximum, and for me that is not unexpected in my experience. However, the GM does show some superiority when installed and compared with these antennas at the same feed point height. IMO this is due to the GM being very tall in addition to the way it uses the full 5/8 wave radiator...working all the radiator in phase.

I agree with you about the way it works. Also remember as you come up through the frequencies the antenna lengthens up to .64 wl and beyond. This is supposed to be the magic number however again I have no personal experience with this (another reason why I built this antenna)

In my checking of my bandwidth curve on my GM it show a sharp rise at both ends of the <2.0:1 curve, but may be right it may be a little sharper at the high frequency end.

Mine does the same. Upper end is a sharper swing upwards to the 2.0:1 point.

Thanks for the welcome. It's appreciated. I haven't finished playing with this bad boy yet - not by a long chalk, so please, anyone, any suggestions or ideas at all no matter how crazy they may sound. Throw them on the table let's see if they'll work.

73 all.

PsiDOC

 

[HomerBB]

Well Done, PsiDOC.

I broke my own rule and paid attention to the speculations that this antenna could not be properly duplicated until the exact same type coax was employed. It appears you have done it otherwise, and beat me to it in the process.

Perhaps the one imperative question to be answered is whether this one puts the same gain on the horizon the original is said to be doing.

Thanks for posting up. Now I guess I'll have it to do.

Homer