Slant Right

Many of you new to 2M SSB will find the antenna that you have been using for FM operation (usually vertically polarized) is just not cutting it on SSB especially when checking into our local Rocky Mountain VHF+ Net held on Monday evenings at 8:00 local time every week. Two things happen: you probably become discouraged by not being able to hear 90% of the other net members and secondly, the Net Control Station will have a difficult time checking you in, if you are heard at all. The general rule of thumb is to use a horizontally polarized Yagi or Omni Directional antennas when operating 2M SSB.

A vertically polarized antenna is going to be more susceptible to ‘man-made’ noise than a horizontally polarized antenna. This is not going to help your ‘signal to noise ratio’ and may negate you hearing any sort of DX stations. Your vertical antenna being used for FM operation is great as noise is not a problem when talking to a ‘box on a hill’. The FM radio has limiters that cut out noise in general prior to the signal reaching the discriminator type detector. This is not the case in the detection of SSB signals where a product or reciprocating detector is employed.

If the situation is such that only one antenna can be used at a location, attention might be paid to having that single antenna work for you in a slight compromise to both modes of operation. If you are using a Yagi to access some ‘box on a hill’ you probably have too much gain in the first place. Unless you really live in a hole a simple quarter wave whip (semi radiating dummy load) should be sufficient to access most of the ‘boxes’ in the area. However; if ‘box DX’ing’ is your aim, plus you’d like to try 2M SSB the answer is called “Slant Right”. Generally placing a Yagi antenna (or any other antenna for that matter) at a 45 degree angle will allow you to operate both modes with only a 3 dB decrease in the stated gain of your Yagi antenna to a vertical or horizontal receiving antenna and of course the reciprocal.

Mathematically we prove this axiom my looking at the Sine or Cosine of Theta, which is going to be 45 degrees when Slant Right is employed (it could just as easily be Slant Left). This is the displacement from vertical or the horizontal. To convert the Sine or Cosine of an angle to decibels (dB), we have to take the Log to base ten of that number and then multiply it by a factor of 20, or in equation form,

dB = 20 log Theta (Sine or Cosine there of).
The situation becomes a little different if the angle is other than 45 degrees. To find the attenuation factor of an antenna at some angle out of the horizontal or the vertical check the following. Example; using a vertical antenna to receive a horizontally polarized signal, as Theta approaches 90 degrees, 20 times the Log of the Cosine of Theta is on the order of –20 dB or a factor of 100 times. No wonder you can’t hear Net Control, right? (or visa versa). A word of caution when using “Slant Right”. If you try and work another station that has “Slant Right “ employed you will be cross-polarized.

Dave W6OAL –

Olde Antenna Laboratory 41541 Dublin Drive Parker, CO 80138