New Sirio 1/2 wave Gain Master

[bob85]

Eddie,
The wide vswr curve of the original gainmaster is one of the few things i do like about them,
If it turns out that it's a regular 1/2wave coaxial dipole stuffed in the original gainmaster tubes with the top section removed @ a similar price, that will be disappointing.

 

[Marconi]

GM 24' at 36' ISO at 27 mhz

Eddie,
The wide vswr curve of the original gainmaster is one of the few things i do like about them,
If it turns out that it's a regular 1/2wave coaxial dipole stuffed in the original gainmaster tubes with the top section removed @ a similar price, that will be disappointing.

Sure it will Bob, price matters. I don't think it will out perform an A99 or the knockoff made over there by enough to make a difference. I don't see it being more convenient for mobile use either.

I think all it is, is similar to an old two piece Big Stick that used a shield folded back on the bottom 1/4 wave section. The Sirio HF might show less losses however, but I don't think it will ever have an SWR band width curve like the Original 5/8 wave Gain Master.

I was not aware that DB's model was 24' feet long. I must have missed that. I believe the only thing that is making his model show a similar SWR bandwidth curve is the added length and being close to a center fed 5/8 wave.

 

[Marconi]

The wide vswr curve of the original gainmaster is one of the few things i do like about them,

I don't know for sure, but I have heard ham guys claim the GM bandwidth is not as functional as one might expect and something about using a tuner. It may have been BS however.

I also recall doing some testing up high and down low on my GM, but all I remember is it didn't seem right to me at the time. I don't have any more details however.

I think the GM has a heat problem in the matching area even if it doesn't pop the matching device somewhere. I've seen mine give me some erratic SWR readings under low power and sometimes get really quite on receive. I could switch antennas and signals were there, but not on the GM.

I had the thought once that the top wire came loose from the brass hub in the top, but the pictures of my lightening damage I posted above shows it is fully intact. I like the antenna, but it is wispy.

 

[The DB]

Lets clarify a few things.

DB, I don't understand any of the matching and design modeling you have posted here. I also missed seeing where you made your T2LT model 24' feet long like Bob suggested.

Bob asked to add a capacitor to a T2LT model to see if it had any effect on bandwidth. When I did it screwed up the tuning to the point of it being over a thousand to one SWR. In an effort to get this high SWR down I made some changes in small increments to the model. First I moved where the feed point was on the antenna, and the capacitor with it. When I found the optimal spot for this I slowly added length to the antenna. To be clear, I started with a near 18 foot antenna, but when SWR settled to its lowest point it was near 24 foot long. That 24 foot length was not a goal or a starting point but a result in itself. At that point SWR was between 5 and 6 to 1.

IMO, this longer radiator is probably what is producing the SWR bandwidth curve that looks similar to the Gain Master. Click here: http://hittman.us/pictures/3-9-16/testswr.jpg
Many of us have likely seen this BW curve shape somewhere on the Sirio Website for their original Gain Master.

If I made my New HF Gain Master 24' feet long instead it being a 1/2 wave at about 17' feet...it would produce a similar antenna pattern to the GM too, and my model does not include the matching device you're showing us.

The radiator length, in and of itself, is not enough to cause this bandwidth, and without some form of matching isn't even enough to get any part of it down to a 2 to 1 SWR match. There has to be something else in play here. That something else is the combination of the added capacitor and a stub match, a stub match that was not simply tuned to get the lowest SWR at one point, but manipulated to put what is essentially an anomaly created by the combination of the capacitor and the stub match in the low SWR region.

So lets see your 24 foot antenna with this bandwith without any form of matching, hell lets see your 24 foot antenna model with any point under 2:1 SWR without any matching.

Your model also shows us a unusual image of the current distribution. Click here: http://hittman.us/pictures/3-9-16/dist.jpg
and I'm guessing this is simply due to your adding the matching device. I've made models before that showed similar current distributions and I found out later the model was broken.

There was no matching added to that model, at that point I have not yet used any form of matching on this project. That came later, and was the last step I did. I have not shown any current distribution of any antenna after a matching system was added in this thread.

Try removing the device temporally and see it the current distribution pattern doesn't look more normal like a GM. You won't have a good match to produce a nice SWR curve, but I don't think that makes much difference in the performance results.

OK, then see for yourself. Here is that antenna's SWR curve before any form of matching network was added.

Whereas the model with the matching system has a very "Gainmaster" like SWR curve that covers almost the entire bandwidth shown with 2:1 or less SWR, you can see that without the matching network added the curve is much more standard looking, and it doesn't give nearly as much bandwidth, in this case, over the same frequency range the difference is SWR is huge, going from near 5 to one at its lowest point to near 15 to one at its highest point.

I know you will probably say that I don't have a clue as to what you are trying to do, and you are correct, but I don't think a matching device is going to broadband this antenna appreciably without physically making the radiator longer.

Just my opinions.

What I was trying to do was see if I could fulfill Bob's request of a half wavelength model with a reasonable capacitance created by a coaxial capacitor, and see if that would affect the overall bandwidth. In trying to accomplish that, following logical steps, that led me to the 24 foot length to make such a design workable. I will say again, I did not start with the 24 foot design, that is a result of trying to make Bob's suggestion work. It is the addition of the capacitor that required this change in length.

The matching device is only a part of the reason why this model sees this bandwidth. The capacitor is another part. I understand why this bandwidth is happening, but it is not an easy thing to explain. Do you understand smith charts? If you do I can easily explain why this is happening, but if you don't understand smith charts the explanation will be over your head.

DB, Eznec warns us in the Manual...that if an object is irrelevant, it can and should be removed.

I agree with this, however, nothing I added to the above models is irrelevant.

The only thing I mentioned that was irrelevant was a result in the image of the gain chart posted when Bob asked about gain over the bandwidth of the antenna. On that same image is a front to back ratio chart, which shows a front to back ratio of 0.02 dB. That 0.02 dB of front to back ratio is what is irrelevant.


The DB

 

[The DB]

I don't know for sure, but I have heard ham guys claim the GM bandwidth is not as functional as one might expect and something about using a tuner. It may have been BS however.

This is not BS. The a99, for example, has a wide bandwidth that can be extended by tuning. The Gainmaster has a wide bandwidth that is difficult to expand with tuning. The difference between these antennas tunability is in how their bandwidths were achieved. They were not achieved the same way.

The a99, for example, has a much gentler sloping SWR curve as you pass out of the useable bandwidth. The gainmaster has a much steeper slope to its SWR curve outside of its useable bandwidth, or in other words, as you move away from its bandwidth in frequency SWR gets very high very quick. It is simply easier to tune the not as high out of bandwidth SWR on an a99 antenna than it is to tune the very high out of bandwidth SWR of the Gainmaster...

From people who have actually tried, the a99 is easy to tune well beyond its designed bandwidth with a tuner, and the Gainmaster doesn't tune well at all.


The DB

 

[The DB]

OK, I think I am going to try and explain what is causing the Gainmaster type bandwidth, at least in my model above. This does involve smith charts, and while I am not going to give a full primer on smith charts, I am going to include a few here for a comparison, and give some information on them.

Pulling one up to start with, this is a center fed dipole with resonance tuned to 27.18 MHz.

There is a lot of information on here, some of which you can ignore. The green line and the pink circle for example, the modeling software would not let me remove them, or at least as of yet I haven't figured out how to remove them.

There is a horizontal center line in the chart. This line represents resonance, or X=0. It is the only perfectly straight line in the chart.

Where some lines cross that line you see some numbers. One of those number is 50. In this case it is in the exact middle of the chart. If you have trouble reading those numbers, look where the green line ends, that is the same point. I guess that unused extra information is good for something here...

The next thing to look at is the red line with the black dots on it. This represents the range of frequencies being scanned by the software and their X and R values plotted on the chart. All of these charts are using the same range of frequencies, and this is the exact same range of the bandwidth in the Gainmater like model I have above.

The last bit of information to look for here is the black circle. This information is not normally present, but I added to these for reference. The black circle represents 2:1 SWR. Everyting inside of this circle is under 2:1 SWR, with the center point I pointed out above being a perfect match.

As you can see in the chart above, the bandwidth of a center fed dipole (in this case in freespace) has a curve, part of which is inside the 2:1 SWR circle. The area within the circle represents the 2:1 SWR bandwidth of the antenna.

This next example is a 1/4 wavelength vertical antenna with four 1/4 wavelength radials.

In this case, we see a curve, again, but none of the bandwidth shown is in the 2:1 SWR or less region.

These lines show typical SWR curves for most antennas. However, as I will now show you, my "Gainmaster" model has a well placed anomaly in its curve that has a certain benefit.

In this case, see how the line that represents bandwidth enters the 2:1 SWR region, then instead of simply curving through the region like the more standard antenna models above, it makes a loop contained within the region, before curving back out of the 2:1 SWR region. This "loop" as I will call it allows the antenna to have more bandwidth in the 2:1 SWR region, thus increasing its frequency bandwidth. If you remove the matching network, this loop does not exist. If you remove the capacitor this loop does not exist. This loop only exists in the model if both are present.

I know this will only confuse some people more, but I hope for some others it helps give an idea of what is happening, and exactly how my model, and possibly Sirio as well, achieved such a wide bandwidth.


The DB

 

[Marconi]

DB.

Sorry, I should not have entered into your conversation with Bob and the T2LT ideas you modeled. I looked your posts over with interest and said I did not understand the modeling, but then I interjected my thoughts anyway, and that was not informative for anybody.

Thanks for the heads-up on the Smith Chart too.

 

[The DB]

No problem.


The DB

 

[Marconi]

DB or Bob, I'm not familiar with the T2LT antenna or its design. Do either of you have a good link to the build or construction.

I've seen a few videos, but none were very good.

 

[camaro1]

made a couple of these for friends to deploy up in trees

 

[The DB]

It's a half wavelength dipole made out of coax. Essentially, the outside of the coax shield is the bottom half of the antenna, and a choke marks the bottom part of it blocking the RF from continuing down the coax after the area you want it to stop. The center conductor either extends past said shield making up the other half, or sometimes another wire is soldered in.

The DB

 

[Marconi]

Thanks guys.

I checked out this video:
and it showed different dimensions for resonance at about 27.405. If you know, what is the frequency for the version you guys did?

 

[The DB]

Ha, he got it in first... LOL found the same pic even, what are the odds...


The DB

 

[Henry HPSD]

http://www.sirioantenne.it/pdf/Id-442-26-02-2016.pdf

 

[Needle Bender]

The only thing that comes to mind every time I see anything about this antenna is, "Why?".

I would've much preferred Sirio invest time & $$ into offering an high power version of the GM instead of this redo of an old Shakesphere Super Big Stick. Well, at least they got it right with the choke. Looks like it's enough turns to provide isolation at the high voltage node where most place a simple current choke.

But they already have a similar antenna which offers 25% more antenna so again my mind flows in the direction of the obvious question, "Why?".