[Elecraft] OT: qrp - antenna is everything?

[Vic Rosenthal]

Tim wrote:
> Hi folks -
>>From you pros - I'm curious. At the bottom of an 11 year cycle is it likely
> that a 5 watt or less qrp rig will still reach anywhere in the world if you
> assume the station can have ANY antenna it wants? In short, is it ALL about
> antennas? 

It's all about db.  You need to get a certain amount of power (usually 
expressed in dbM, db over 1 milliwatt) at the antenna terminals of a 
receiver to support communication.  You start with a certain amount of 
power (say 1 watt or 30 dbM), add the antenna gain on both ends, and 
subtract the path loss.  If you have enough dbM at the other guy's 
receiver, he will hear you.

So if you need another 10 db, you can increase power to 10 watts or 
install an antenna with 10 db gain compared to your original antenna.

At the peak of the sunspot cycle, the muf (maximum usable frequency -- 
the frequency at which the ionosphere reflects radio signals) goes up, 
so the higher bands become usable.  The path loss on the higher bands -- 
when they are open -- tends to be less than on the lower bands, so it's 
usually easier to make worldwide contacts with low power and simple 
antennas.

At the low part of the cycle, the muf may never rise high enough to open 
the high bands at all; the path loss is almost infinite and even the 100 
KW shortwave BC transmitters with their huge antennas don't get through.

During the low part of the cycle, the low bands tend to be quieter and 
so are actually better for DX than they were during the high part.  But 
the path loss is generally higher than it would be on the high bands, so 
you need to get more ERP (effective radiated power) out of your antenna.

When considering how to increase your ERP, it's generally considered 
advantageous to improve your antenna, since that improves your ability 
to receive signals as well as to transmit.  Although it's quite 
difficult to build an HF antenna that will give you 10 db gain over a 
good high dipole, it's not hard to get 20 db over a Hamstick!  And 20 db 
makes 1 watt sound like 100 watts.

Personally, I put up the best antennas that I can from a standpoint of 
cost and practicality, and then increase power as needed for reliable 
communication.

Vic K2VCO