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1-7 of 7 messages
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Steppir Relative Gain / 350Khz to 25Khz in DB?
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by NN2X on November 4, 2005
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We all know that antennas have trade offs, for example, if building a Yagi Antenna, you have a choice to optimize the forward gain, Back to Front isolation, and bandwidth (To name a few)
Here is my questioned for the Antenna experts.
The Steppir Manufacturer, as you might be all aware has the ability to adjust the elements, and therefore optimize the antenna to either Forward Gain or the Back to Front.
Here is the interesting point, the bandwidth can be adjusted to 25KHZ, meaning as you go up and down 20 meters the elements are changing and the Bandwidth is only 25Khz, besides the great ability lower the overall noise one would think, since you give the up on the Bandwidth, you could optimize the forward gain (Or Back to Front).
There is one constant on the Steppir antenna, which is the spacing we know from practice and theory that there is not much loss in forward gain or Back to front, especially in the Steppir configuration (10 through 20). One thing that is nice you can calculate the difference in db, based on math.
Where I am at in a loss, is if the Steppir can give up the bandwidth at 25Khz, (Let say 350Khz is Normal) what is that gain in the forward direction when compared to 350Khz
I know there is a formula called DB = 10*LOG (BW / BW) = Equals 11DB or so.
We know that the antenna can not achieve 11DB of gain, (I think this has to do with the Noise Floor), but nothing to do with the gain.
What I am curious about is what is the calculated gain and the associated formula, if the bandwidth is less, I know there has to be some forward gain!
What I am thinking is that the none optimized spacing on the Steppir is made up on the narrow bandwidth that it work under (25Khz), but I would like to calculate both the loss on the none optimized spacing and the gain that would be achieved by lowering the bandwidth from 350Khz to 25Khz.
If my assumptions are correct, this would be a great selling tool for Steppir
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RE: Steppir Relative Gain / 350Khz to 25Khz in DB?
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by K4SAV on November 4, 2005
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The bandwidth of the SteppIR at any particular setting is not 25KHz. If you have the rig interface, it automatically re-adjusts the element lengths every 25 KHz, but that says nothing about the bandwidth at each setting. If you set the controller to manual, then you can move the frequency without the antenna changing. Then you can observe the bandwidth for a particular setting. This will be different on each band.
The SteppIR's design is a compromise (as are all antennas) for gain, F/B, element spacing, and bandwidth. In this design process, it was possible to treat bandwidth as a minor consideration, since the elements are adjustable. This allows increased performance for the other parameters. You can't easily calculate all the other parameters in a simple formula, when changing one parameter such as bandwidth. You have to model and simulate the whole antenna at all frequencies of interest to determine all the parameters.
Jerry, K4SAV
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RE: Steppir Relative Gain / 350Khz to 25Khz in DB?
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by NN2X on November 4, 2005
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Jerry, Thanks for the reply...
The only point here for me, is the bandwidth of the antenna,
I have an email from Steppir, that indicates 25Khz of Bandwidth (I am assuming at the 3 DB Points).
Let say, we have a constant number for F /B, a constant a compromise on optimize spacing of 0.5 DB loss, however the antenna is normally designed to support 350Khz, and now is 25Khz, the trade of on bandwidth should be able to give to either the F/B or forward gain.
The 5 million dollar questioned, is what is being compromised by the spacing (Lets say 0.5DB) can one make up for with the 25Khz? (Because most antennas are designed to support 350Khz on lets say 20 METERS)
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RE: Steppir Relative Gain / 350Khz to 25Khz in DB?
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by K4SAV on November 4, 2005
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As I said, the bandwidth of the SteppIR is not 25 KHz. If they gave you an answer like that, they must have misunderstood your question. I just made a few measurements on mine (4 element SteppIR, 250ft of coax). The controller was set to manual, so the antenna is not changing length as I change frequency.
MHz____SWR
14.0___1.18
14.1___1.25
14.15__1.3
14.2___1.4
14.3___1.5
As you can see the bandwidth is much wider than 25 KHz. The bandwidth does change on different bands.
Jerry, K4SAV
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RE: Steppir Relative Gain / 350Khz to 25Khz in DB?
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by NN2X on November 4, 2005
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Jerry; Yes indeed they must have misunderstood the questioned.
My next questioned, is it possible than to manually tune the antenna to meet a narrower Bandwidth, so one can trade off the Bandwidth to forward gain?
Again thanks for responding, and I am very pleased I am talking with a person who actually owns the Steppir Antenna and provide real time results!
You can't ask any more than that!
I am in Kuwait, I should be able to send a few CQ calls, in a month, I would like to catch you on the air!
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RE: Steppir Relative Gain / 350Khz to 25Khz in DB?
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by K4SAV on November 5, 2005
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A minor correction to an earlier comment, the SteppIR in manual control mode has 25 KHz segment steps, but in automatic mode it adjusts elements lengths every 50 KHz, not 25 KHz.
Yes, the SteppIR is fully programmable. You can design your own antenna, feed this data into the controller which will store it.
In order to do that, you need to simulate the SteppIR in some kind of antenna analysis software, in order to determine what you want the antenna to do. You can't change element spacings, but you can change all element lengths. There are some limitations. Although you can reprogram all the segments dedicated to the ham bands, if you reprogram frequencies outside the ham bands, you have to use up some of the memory slots allocated to ham frequencies. Within the hams bands, there are three seperate antennas loaded into the controller, one for forward direction, one for 180 degree mode, and one for bi-directional. These three antennas are selectable at the push of a button. That allows the antenna to reverse direction in 3 seconds or less.
Although designing antennas and reprogramming the SteppIR is possible, only a handful of hams will ever do this. A useful feature that does not require any software analysis is to readjust only the driven element length to reduce SWR caused by other objects close to the antenna. This is a simple procedure.
Jerry, K4SAV
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RE: Steppir Relative Gain / 350Khz to 25Khz in DB?
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by WB6BYU on November 7, 2005
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A useful yagi modelling applet available online is:
http://fermi.la.asu.edu/w9cf/yagipub/index.html
With this you can experiment with element lengths to
your heart's content.
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