Helical or paddle antenna for both IEM and WL mics

Paul Johnson

Freshman
Oct 27, 2012
89
6
8
I'm sorry but that is completely wrong. Antenna design is not linked to transmit or receive it is 100% related to polar pattern and gain. A wonderful antenna that has just the performance you want is not special or unique to receive or transmit. If you look at cellular antennas you will not find them in two sections. There is some confusion in some quarters because for efficient transmission the antenna must be matched to the feeder cable and transmitter for optimal signal transfer- something well understood VSWR. Antennas on comms towers are normally designed for omni-directional coverage - as in they are vertical radiators and their polar pattern from above is a nearly perfect circle - equal signal strength in all directions. This is the typical vertical antennas on radio mic receiver units - these may be helical, but usually nowadays are just a ¼ wavelength of wire inside a sheath. There is no helical winding as you would find on bands lower than 200MHz or so, where antennas ¼ wavelength long are a bit big. They can also be directional with beam antennas if needed.

Directional antennas have radiation patterns very similar to cardioid or hyper-cardioid mics - and longer shotgun mics look very similar to yagi antennas of 8 or more elements.

Transmitter sites use separate antennas to get additional separation, or where they may wish to have different polar patterns - or they can use combiners and filters to use one antenna connected to a transmitter AND a receiver, as long as the frequencies are different.

Receive antennas are often poorer designs - it really doesn't matter of they are 50 Ohms, or 40 or 60 - on receive the different has a very small impact. On transmit, the transmitter may detect the poor match and throttle back a little to prevent damage to the output stage.

Active antennas are the exception - they will be for receive use only - electronics doesn't;t like RF going the wrong way. The preamp is the issue NOT the antenna, which is totally uninterested in the 'direction'. Indeed - consider a walkie-talkie. That single antenna does both jobs perfectly well. This post to a long dead topic is just poor information, sorry Frank
 
Check out the RF venue CP Beam. Helical. Folds flat into a 2u Rack draw. That thing is awesome. I bought one to take out on gigs when touring as what is usually supplyed is Fins. what a difference it made for me. Bigger stages it reached the guitar tech on the other side with no issues. The null behind was a slight problem that I had to go to a whip for my antenne but it was worth the trade off.
 

Paul Johnson

Freshman
Oct 27, 2012
89
6
8
The reality of on stage radio use is that the distance from stage left to stage right is so small that a full signal strength reading from even a low power wireless unit is not a feat of any kind. 1W can get you up to the space stations in orbit. Line-of-sight is exactly what it says. If you can see it, it will work. The issue is things in the way, and reflections. Those dead spots we all have noticed. Antennas can have gain, but usually at the expense of coverage. If you tour a show, then your system that works in one venue should work in another, unless things make you move your gear and people in relation to each other.

We also did not cover polarisation changes - very tricky when you look at hand-held's being waved around. A vertical antenna on the receiver can be totally solid, but rotate it through 90 degrees and the signal strength can drop to almost nothing. We spoke about helical antennas - usually a way to produce a functional antenna in a smaller package by coiling the wire. We can also have another helical antenna where a spiral is used to produce an antenna that works effectively on any polarisation - so rotating the transmit antenna doesn't do anything. We can add reflectors, creating a more cardioid pattern, with a distinct 'rear'. We often think of the paddle antennas as 'beams' - but most are log-periodic designs capable of operating over a wider frequency range. They do have a directivity - but not as much as you'd imagine. With diversity operation, the idea really is to make sure that there are no zero level dead spots, not that there is maximum signal. The plan is just to create coverage where the signal strength remains good, everywhere people will be working, and not waste it on areas that don't matter.

There is NO single antenna that does this. Simple dipoles, small yagis, log-periodics, helicals and other designs are just tools for different jobs. It is NOT magic and it is NOT something where any of them at any cost will solve a problem.