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 external usenet poster First recorded activity by RadioBanter: Oct 2016 Posts: 73
[FOAR] How effective is your station?

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Posted: 07 Feb 2019 05:56 PM PST

Foundations of Amateur Radio 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...
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