Re: RTrak-HAB antenna thoughts
- Hi Ben
Most people use either a simple upside down 1/4 ground plane, vertical dipole or wire J-pole on the balloon. All these give good radiation patterns sideways with varying degrees of a null directly below the balloon. I use a single vertical radiator with a single counterpoise which gives an odd shaped radiation pattern that doesn't have a null directly below it. For a mobile tracker my favorite is a simple 1/4 mag mount. A 5/8 will help receiving the signal once the payload is near or on the ground, but is has a strong null directly above it.
The worst situation for reception will be when you are directly below the payload. The null on the payload and the null on your car's antenna will tend to add together and you'll notice a significant reduction is signal strength. I've heard this referred to as the "cone of silence". Occasionally it's enough to make it difficult to receive the payload. One option are to stay out of this area below the balloon. A simpler solution is to slap your mag mount on the side of the car. Really! I did this on one flight and my weak signal from directly above returned back to full scale.
In short, you don't need any special antennas. Our balloon in mid Saskatchewan last weekend, running 300mW was heard in Manitoba, Alberta, Montana and North Dakota, all with no special antennas. I was also able to copy it about 80% of the time with my TH-D72 with a rubber duck at a range of about 40 miles.
In short, keep it simple, try to keep 10 miles or more away from directly below the balloon and get creative if you need to like moving your receive antenna around. You may also want to take an extra hand held along so you can play with different antennas.
73, Bruce - VE5BNC
SABRE - http://ve5aa.dyndns.org/balloon
--- In RTrak@yahoogroups.com, "airsix73" <ben.messinger@...> wrote:
> I'm preparing my first balloon launch and trying to decide on antennas for the mobile ground station as well as the balloon. I'm a new ham, and nervous about keeping a strong enough signal over 25-30 miles with just 350mw transmit power and random orientation. Suggestions?
> For best front-to-back ratio there are some really neat antenna designs (patch, bi-quad with reflector, yagi, 2 and 3 element quad) but they aren't very conducive to balloon work!
> For those of you who've done this before, what are your recommendations? I'm sure I'm over-thinking it, so I'd love to hear what others have done with success.
- Ben KF7VZR (got that from a June 22 message) wrote...
> My documentation says nothing about TX audio level...Deviation is important. If it's too high (within limits) nearby stations
> They've both been played with...
may still be able to decode the tones. Distant ones where your signal
is weaker may not be able to. You have probably heard this on a voice
repeater or even on simplex. A distant and noisy station can be copied
via a repeater if he backs off from the mic. If he starts shouting, the
deviation goes up. More energy is outside the passband of the receiver
and eventually the signal is too noisy to copy or the squelch might
even close. If you are simplex, you can try opening your squelch. If
you are on a repeater, you're out of luck. It's the same with packet.
You are better off having the deviation set properly. It can be done
by ear, but a deviation meter or service monitor would be better.
Lacking one, just crank the deviation all of the way up and then
start turning it down. When it starts to sound quieter, turn it down
some more. It will get you in the ballpark, but checking the actual
deviation would be better.
Perhaps you could check the actual deviation before you change
anything. So... could over-deviation explain why only one iGate
73 es cul - Keith VE7GDH
"I may be lost, but I know exactly where I am!"