how is the sirio tornado 27 matched

[davev8]

how is the sirio tornado 27 matched ??? the coil dont have a tap...its just a coil ...there must be something else...maybe the rod from the feed point to the coil is a capacitor? a tube with a rod up the center ...bit like a non adjustable gammer match ...or am i missing something

i dont no if this photo link will work
photo not work a good shot in this vid at 30 sec in

 

[The DB]

how is the sirio tornado 27 matched ??? the coil dont have a tap...its just a coil

Here is a link to the installation manual.

Looking at it, it appears that it is a coil loaded antenna like a mobile antenna, essentially shortening an electrical 3/4 wavelength antenna to a physical 5/8 wavelength. To tune the antenna, they give you an antenna length starting point of 1120mm, and they say to adjust this length to lowest SWR with an SWR meter.

...there must be something else...maybe the rod from the feed point to the coil is a capacitor?

Good thought, but not necessarily. The capacitor and the coil in this configuration would create something called a parallel resonant circuit, which would, in and of itself, present a high impedance to the feed line, which would be counter productive. The Maco v5/8 antenna is like that which is why you need to tap the ring to find a low impedance point to match that antenna. Not all 5/8 wavelength antennas are designed that way. The fact that their is no tapped coil rules out that possibility for this antenna.


The DB

 

[undertaker]

Mine works great swr 1.1

 

[davev8]

i am very interested in how different antennas matching systems work and how it affects things like bandwidth etc ..so if i am reading what you say correctly ..it must mean a 3/4 wave will match up with no matching device like a 1/4 wave ...if so i did not know that .....obversely if i did i would realize how it worked thanks

 

[The DB]

i am very interested in how different antennas matching systems work and how it affects things like bandwidth etc

Most matching systems will narrow the bandwidth by nature, although their are exceptions. The reason for this is the antenna has a bandwidth, and the matching circuit also has a bandwidth. When both are in tune you have a match, however, as you move away from that tuned point both systems are working against having a good bandwidth.

Their are some electrical lengths the provide better natural bandwidths than others, for various reasons. These lengths are easily found, namely, any electrical length that is a multiple of 1/4 wavelength. In the case of this antenna, we have a 3/4 electrical wavelength element that is physically shortened to the 5/8 wavelength length with a loading coil. Some people will tell you that all 5/8 wavelength antennas are this way, however that is not a true statement, and is actually mostly false. Most 5/8 wavelength antennas, instead of shortening a longer electrical length, simply use a matching circuit to correct the phase (some people will call in an impedance) mismatch that is naturally present with a 5/8 wavelength antenna. This is not the same as electrically shortening an antenna.

Their is actually an antenna out their that is an electrically lengthened 1/2 wavelength antenna to a physical 5/8 wavelength. That is the imax 2000, and they do that to essentially use the same matching system as their half wavelength a99 antenna.

Back to matching systems and bandwidths. As I said, their are exceptions to the normal matching system lessening the bandwidth, but these are few and far between. The Gainmaster, for example, uses an anomaly in the impedance curve to create a large bandwidth. However, most other antennas with a wide bandwidth essentially use losses to achieve their wide bandwidths.

it must mean a 3/4 wave will match up with no matching device like a 1/4 wave

The 3/4 wavelength element will create a higher impedance than a 1/4 wavelength section, however, this antenna also has several devices that lower that impedance back down to compensate built in as well. For example, the loading coil will lower the impedance of the antenna. The four elevated radials will also, by nature, lower the antenna's impedance as well. Essentially, when it comes to antennas like this, it is all a balancing act.


The DB

 

[davev8]

Thanks DB for taking time to answer my enquiry