Antenna Query

civdef

I was messing around with APRS this afternoon, using AGW Tracker and AGW Packet Engine, using an MV-3300 with standard rubber duck antenna as receiver, anyway I was having difficulties receiving a clear signal on 144.8, lots of interference - and I was messing around with the receiver trying to alter its height, direction etc, until I noticed that I was getting the best reception by holding the antenna in my hand.

I know very little about antennas, and always understood having anything touching them was a bad idea, so what gives?

watty

"rubber ducks" on small radio behave strangely.

Also if the problem was RF stage overloading, by another signal, then reducing it will help.

I've no idea what a MV-3300 is. I use a dual band watson "skinny" rubber duck on my Alinco DJ-V5 which did work on Packet in Limerick before it was turned off.

The Yaesu 817ND has a larger rubber duck for 2M, 6M and 70cm. Both aerials are very very poor compared with the mag mount dual band whip on car.

civdef

Sorry, one of these (got the name wrong)

http://www.javiation.co.uk/mvt3300.html

The_Conductor

The MVT3300 (and indeed the tuner in all the handheld Yupiterus) are incredibly sensetive. As per what Watty said- sometimes effectively cutting the efficacy of the antenna can have the effect of removing a stronger signal that may be causing overloading from an adjacent frequency.

I've had fun playing with a few different Yupiterus (I've 4 different ones- thanks to an ebay auction from Israel I won about 2 years ago) and a range of antenna for them (sourced them both on the net, but also through CQ Communications on the quays). Even on handsets of the same make and model- the sensitivity of the tuner can vary to a very surprising degree. Its well worth while investing in a proper antenna for your handset- the rubber thing does not showcase the potential of the handsets to any extent at all. A decent whip- will really open new horizons for you.

experimenter

Get an external antenna and you're be hearing fine.

I have used APRS both in the car and shack but since the novelty has disappeared.

civdef

Hi, to update things, I got hold of a discone antenna, and things are perfect now - thanks for the help.

Experimenter, I've been looking at APRS for a while as a tool for SAR ground teams, both for coordination and record keeping - I think the Mountain Rescue people are doing something similar (but with better sponsorship and nicer equipment )


I'll throw a frequency question at ye - the experimenters use 144.8 or similar for APRS, with seemingly excellent results in terms of range (i.e. several miles with handhelds). I did some experiments using handhelds on 456-462Mhz and obviously the standard rubber duck antenna. The results were disappointing, typically less than 1/2 mile in any sort of realistic terrain, which isn't enough for operational tracking. I also have access to frequencies in the 66-88Mhz range, should these perform better or is it likely to depend more on suitable antennas?

watty

66MHz to 88Mhz is much better.
But you need at least real 1/4 wave whip, not rubber duck.

The other solution is a Packet repeater on a high site. Unlike a voice repeater it doesn't need 2 radios and Duplex filter.
It can have 68MHz and 460Mhz radios and store/Forward a message received on either on both. I set up such a system on 70MHz and 144.600 on a Tipperary hill top a few years ago and worked fine with 500mW rubber duck handhelds over 30kms range. I think it may be offline now.


But even the 460Mhz ish band you can get much better. Depends on power and aerial. Rubber Ducks often have no or negative gain. A flexible 5/8ths or 1/4wave isn't so big at 460MHz.