Quote:
Originally Posted by James Duncan
I feel that you are getting too much conflicting info
|
Therein lies the problem. There are as many recommendations as there are people. All of them will work, to different extents. All are affected by your location.
But which is best?
The measurement of any antenna, with enough precision to make comparisons valid, is a major undertaking and is famously expensive. Such undertakings are inevitably done only for military, broadcast, etc. applications where the money is available. This means users with however much clear land it takes.
The evaluation of HF antennae in cluttered domestic environments has been left to the amateur community, which seems appropriate, because we are the people who actually use such things.
Unfortunately we can't afford open area test sites and tons of equipment. We form our opinions of antennae from using them. S meters have various sensitivities, differing by much more than the gains of most antennae. Band conditions vary be even more. Some people are more careful than others, using relible beacons rather than whatever distant stations they come across. Beacons are fixed power and fixed antenna pattern so received strength variations are left to propagation and your antenna.
No-one else has quite the same location as you, so you really are on your own, I'm afraid.
There are pages and pages of articles on antennae in the likes of QST, all based on finite element analysis by programmes like MININEC. They can be interesting, but don't model your surroundings.
So that leaves generalisations:
If you live in a housing area, there is going to be terrible levels of RF noise across the lower HF/MF bands through all waking hours. Loops and balanced antennae in general, are less susceptible to this noise, and if the noise is a few dB lower from an antenna, then you can read signals a few dB lower. Insensitive antennae are OK on receive if they make the noise go down more than they reduce the signals. Verticals and asymmetric antennae are moresensitive to enviromnental noise.
Verticals can give better low-angle radiation than too-low dipoles. A popular DXers delight is the Four-Square array of verticals with a phasing box to steer it.
There is no best antenna. It's all just compromises.
There are a few things which are dependable.
Open wire feeders are much lower loss than coax cable. Coax is more convenient, though.
If you use an antenna which is not naturally resonant on your chosen frequency, you can fix this with an ATU. But this meens your feeder is running mis-matched and that multiplies the effect of feeder losses. So low loss feeder comes into its own - If you have a clear route into the ATU in the shack. Or you could build a remotely operated ATU and mount it at the antenna feedpoint. Then, coax is a great choice.
It's quite easy to lose more than half your transmitter power in an ATU and feeder. Running a balun on the antenna side of an unbalanced ATU can be even worse.
Coax cable works best in a controlled-impedance environment. Use it between a radio and an ATU or between a radio and a matched antenna. Avoid it between an ATU and an unmatched antenna.
Open-wire feeder is the least-bad choice for unmatched operation. It doesn't need screening from things away from it, but it you don't want things too close to it. Routing it can be a pain.
Expect to try a number of different antennae. Set things up so you can change things around. Use temporary lash ups. Only invest real effort or money when you've found what works for you.
Of course, we'd all like you to duplicate whatever we have 'cos it gives a nice boost to the ego
I had access to a nice, large, anechoic screened room along with calibrated measurement antennae and spectrum analysers. It was fun to make a few scale model antennae and try them out. But I didn't learn as much about the antennae as I did about modelling their environments!
Have a play, have fun.
David