Yagi or Omni...

[Bluenoser337]

I am working on a system that has 407 MHz system that has a Dataradio and Omni antenna on each end. The sites are about .6 miles apart, with no obstructions between. Just starting to investigate communication problems. Would a Yagi be a better choice for one of the stations, or should the Omni be fine? What's the rule of thumb? Sorry, details are sketchy.

 

[biff44]

There are means of testing the link's "bit error rate". Get set up to do that, and some day when it is raining heavily do the bit error rate (BER) test and see what is happening. If you are getting 10^-12 bit errors, forgettaboutit.

 

[VEBill]

When looking into any communications problems, one of the first things to do is LISTEN to the receive audio. Learn what the good signal sounds like, and then you might be able to aurally detect (with your ears) if there is some sort of interference, or noise burst, or weak signal, or whatever.

You certainly don't want to be hunched over a BER instrument for three or four weeks only to later discover that it is simple interfernce from some defective taxi radio (or whatever...).

This trick doesn't work as well for wide bandwidth signals.

 

[Bluenoser337]

VE1BLL....I like your idea. Thanks!!

 

[Higgler]

If you get the omni, you can increase it's gain towards any direction by adding a flat grid of wires (or metal plate) 7.2 inches behind it to make it directional if you want to see the difference. Make the grid at least 16" tall and width can vary from an inch to many feet. If it's an inch wide, you've added a dipole reflector behind it. If it's much wider, you'll get some increased gain. You've essentially started to make your own Yagi.


At 407 Mhz, that's a wavelength of 29 inches. this is essentially a 2 element yagi.

Lot's of other options to make your increase in gain 5 or mor dB.

kch

 

[MikeSundstrom]

Also, a simple site survey with a portable spectrum analizer will go a long way towards eliminating any adjacent signals / EMI RX type problems. Use max hold and check the screen every few hours.