ARLA/CLUSTER: Episódio 192 da série " Foundations of Amateur Radio ": Quão eficaz é a sua estação?

[João Costa > CT1FBF]

Foundations of Amateur Radio #192

How effective is your station?

We tend to spend most of our energy looking at antennas and power to
evaluate how well our station works. Based on a better antenna or more
power, you're likely to make more contacts is the general gist of the
process.

Being a QRP operator, power rarely comes into the conversation, 5
Watts is what you get, leaving antennas as the prime method of
discovering how effective we can be.

Recently I received an email from Layne AE1N, pointing me at an
article he wrote on the Nashua Area Radio Society website titled: It's
all about the decibels - factors in enhancing station effectiveness.

The article, goes into great detail in looking at an alternative way
of measuring how well you're doing and builds on the December 2013 QST
article - How Much Punch Can You Get from Different Modes?

In our hobby we measure using a thing called the decibel. I've spoken
about it at great length previously. The way to use it is to compare
something against something else. Using the metric used in the QST
article we take as a starting point a modern transceiver, using 100
Watts, CW into a half-wave dipole at 30m.

Everything we're discussing from here on in, is related to that
starting point, the zero point. I should also make clear that we're
talking about the ability of the receiver to decode your message, not
the strength of the signal.

If you were to use the same radio and instead of using CW, used AM,
you'd have a station that was 27 dB worse off. That is, your signal
would effectively become harder to hear by 27 decibel. On the other
hand, you if were to replace the half-wave dipole with a 4 element
Yagi, your station would be just under 7 dB better off, that is, it
would be easier to hear you by 7 dB.

Of course you can combine AM and the Yagi, adding the two measurements
together, coming out at minus 20 dB, which means that compared to a
100 Watt transmission on CW into a half-wave dipole, the same 100 Watt
transmission on AM into a 4 element Yagi would still be harder to hear
by 20 dB.

If you go from CW to SSB, you'd be 17 dB worse off, or SSB is 10 dB
better than AM.

Note that when I say better and worse, it's about how much your signal
can be decoded at the other end, using the same receiver, antenna,
etc.

The whole article includes comparisons between CW and FM, CW and RTTY
and so-on. RTTY is only 4 dB worse than CW, but most transceiver
manufacturers recommend that you reduce power to a quarter power, that
is, 25 Watt instead of 100 Watt when using RTTY or Digital modes, so
you end up losing 14 dB for that, making RTTY slightly worse than SSB
if you follow the manufacturer instructions to reduce power.

This isn't all doom and gloom however. Even though CW is very
effective, we can improve things in other ways. For example, using
PSK31 gives you a 7 dB head start, switching from CW to JT65 or FT8
gives you 25 dB. Even if you take into account the reduction from the
loss of full power, 14 dB, you still end up in front by 11 decibel,
which is more than you can get from upping power from 100 Watt to 400
Watt which only gets you 6 dB.

Adding an 11 element Yagi gives you a similar improvement as changing
from CW to FT8, just over 11 dB, and using 1500 Watts is only slightly
better at 12 dB.

The point I'm making is that you can use this idea to figure out how
to get your signal heard. More power or a bigger antenna is only part
of the conversation, picking the correct mode is just as important.

Of course, the 11 dB gain you get from moving from CW to FT8, even
when reducing power, is one of the main reasons that it's so popular,
much easier to change mode than to build a new fancy antenna.

One more thing, what of the 5 Watts vs. 100 Watts we started with, 13
dB. That's significant, but if you were to use 5 Watts FT8 into a
quarter-wave dipole, using 100% of the 5 Watts, you'll actually be 12
dB better off than the same station using 100 Watts CW.

Check out Layne's article for a reference to QST and a whole lot more.
It's a very useful way of looking at how your station can be very
effective, even if you're QRP.

I'm Onno VK6FLAB