[HCARC] Antenna Questions Of The Day

[Gary and Arlene Johnson]

Thank you Kerry - you just saved me about $50.00 for the book which is on 
"sale" until midnight tonight.  That surely is worth a ticket at the next 
meeting (from me, not Marylin).  Of all the books other than the study 
guides the best books I have purchased have been the Operating Manual, Low 
Band DXing, and the Antenna Book.  The Handbook is way too technical to be 
of much use - I guess there are good nuggets of info in it, but for antennas 
they just referrence the Antenna Book.  I have multiple copies of the 
Handbook ( the older ones are available for less than a dollar on 
Amazon.com) and each has some good ideas about how to operate which is where 
I need to spend a lot of time once I get the K3 together.  Not only that,b 
ut they are fun reading (get a life Gary).

73's

Gary J
N5"BAA"

Gary J
N5"BAA"
----- Original Message ----- 
From: "Kerry Sandstrom" <kerryk5ks at hughes.net>
To: "Gary and Arlene Johnson" <qltfnish at omniglobal.net>; 
<hcarc at mailman.qth.net>
Sent: Sunday, September 23, 2012 3:33 PM
Subject: Re: [HCARC] Antenna Questions Of The Day


> Hi Gary,
>
> The diameter does make a difference.  Larger diameter tubing will have a 
> wider SWR bandwidth and the antenna will be a little shorter.  There are 
> formulas for calculating the length for different diameters and they may 
> even be in the antenna book or ARRL Handbook.  For reasonable tubing, its 
> just a couple percent.  If you use the standard length formula and 
> calculate the length for the high end of the band, that will probably be 
> good enough except on 80 meters.  The dimensions should be in wavelengths 
> which should dramatize the fact that for HF any sensible tubing is very 
> small.
>
> What its made of doesn't really matter within reason.  Poor conductors 
> will have some additional loss but I don't you can notice it.  The wire 
> will be narrower SWR bandwidth but if you use an antenna tuner it wont 
> matter. Copperweld, copper, and aluminum wire are all used successfully.
>
> Yes tapered sections will have a length that is in between the length of 
> the biggest tubing and the length of the smallest tubing, but again the 
> difference is great.
>
> The point of the roller inductor is to add inductance so the effect is 
> actually a lot bigger than just the length of the wire.  When you are 
> matching a load like an antenna to a transmitter, there are two goals: 
> first, you want to cancel out the reactive component and, second, you want 
> to transform the load impedance to the output impedance of the 
> transmitter. It doesn't matter which order you do it in.  Depending on its 
> length, an antenna impedance can look inductive, capacitive or resistive. 
> Usually its got some reactance and some resistance.  If the antenna is 
> capacitive, you need to use inductance to cancel it out so you have a pure 
> resistance.  An antenna tuner does both the cancel the reactance and 
> transform the impedance.  It typically has 3 variable components, two 
> capacitors and an inductor.  There are several possible configurations, 
> however, they all will work.
>
> Adding or removing 2 foot sections might be good at 80 m but is probably 
> to big a step for the higher bands.  Personally I would make the antenna 
> as long as I could and then rely on an antenna tuner to adjust it to the 
> transmitter.
>
> I'm sure you've heard me talk about "magic" before.  The 43 foot vertical 
> falls into that category!  Arguably the best ham radio HF vertical is and 
> has been for decades the Hy-Gain 18-HT  Hy-tower.  It is over 50 feet tall 
> and has a couple sections of triangulatr tower at the base.  It covers 
> 80 -10 primarily the old bands although I think you can use it on 30 and 
> 17 m also.  The only reason I don't use one is they cost ~$1000.  A couple 
> years ago people started pitching 43 feet as the optimum length for a 
> vertical.  You have to use some kind of a tuner with this length.  A 66 
> foot vertical would be a better choice but is difficult to support!  In 
> any event, the bigger the better, size does matter.  If its not an odd 
> multiple of quarter wavelengths long, its going to need a matching device 
> such as an antenna tuner.  Even if it is an odd multiple of quarter waves 
> it is still going to need some kind of matching since its impedance is 
> about 35 Ohms. A 33 foot vertical is resonant for 40 and 15 m but is too 
> short for 80 unless you use somekind of loading and/or matching.  You also 
> need a matching system or loading to make it work on the other bands.  A 
> 43 foot vertical would work better than a 33 foot vertical because it is 
> bigger but it may not be as easy to match.  You probably would have a 
> difficult time seeing the difference.
>
> As I've said before, you can make anything work and with a tuner, it 
> probably won't make much difference what you use.
>
> Yes, I just saw your latest e-mail.  Remember the league is out to make 
> money.  They have two ways, accepting donations or selling books and 
> magazines.  I believe they produce books and magazines to make money and 
> not to make a better life for hams.  Excellent antenna modeling software 
> is available free from our government!  It is not and never will be simple 
> to use however it is well documented.  A good model is simply a starting 
> point. It will get you into the ballpark but even if you follow the design 
> dimensions exactly it will still take some playing around to make it work. 
> I haven't seen the book but I can't believe it will really make it any 
> easier.  In order to do an accurate model of a real antenna you have to 
> know what the ground parameters are, what conductive or lossy objects are 
> near your antenna, The dimensions and configuration of everything 
> conductive on your antenna, the characteristic of your ground system and 
> transmission line, etc.  Beyond a point, modeling is counterproductive. 
> It will let you look at them impact of changes on performance, but the 
> actual performance and the match in particular are something you best do 
> experimentally.
>
> Have fun,
>
> Kerry
>
>
>
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