Date: Thu, 8 Dec 2016 04:02:18 -0800
From: Catherine James <catherine.james@att.net>
To: Amps Group <amps@contesting.com>
Subject: [Amps] S-units
Could the modern ham community please stop pretending that 1 S-unit = 6 db?
It may have been true decades ago, but it is far from true in the large
majority of modem ham transceivers.
When I installed my hexbeam, I saw about 1 - 2 S-units improvement on my
TS-590S. This antenna is well-known to deliver about 3-4 db.
Let's talk db, a unit that is clearly defined and when which everyone agrees on
the definition. S-units are just for a casual meter check during QSOs.
73,
Cathy
N5WVR
### Very true. Just switch on the typ 6db attenuator on RX....and watch the S
meter drop a helluva lot more than 1 S unit.
Some of the yaesu xcvrs are close to 5 db per S unit between S7 to S9. Below
S7, its more like 3-4 db per S unit. Below
S4, they are typ .5 to 1 db per S unit. Switch in 12 db of padding on
RX....and watch your S meter drop through the floor.
## Try this some time. Shut off the AGC, then back the RF gain way down..and
crank the audio gain up a bit. Then get the
other guy to shut off his amp. Then you will actually hear the audio drop off
XXX db. I had a buddy start at 1500w, then
every few minutes cut the power in half....and every time he did that, I could
easily hear the 3 db drop in audio. The ear can easily
discern a 1 db difference in audio levels, provided they are barely perceptable
in the 1st place. Buddy started at 1500 watts, then 750, then 375,
and so on, till he was down to just 11.72 watts.
## Collins gear was touted as 6 db per s unit..... but that only worked for
whichever band you calibrated it on. On my old drake
R4C receivers, they had 3 x calibration pots for the S meter. 1 uv was S3.
30uv was S9. 30,000 UV was 60db over S9. It worked
out to aprx 5 db per S unit.
## Then my FT-1000D is 60 uv for S9. The FT-1000MP-MKV is slightly more....
and way more, like 190 uv, when pre-amp shut off.
## then we have the goofy xcvrs like Icom, with all pre-amps on.... is just 7
uv for S9. S meters are completely meaningless. If I switch from
100w to 1000w, and the other fellow doesnt see exactly 10 db difference, then
his S meter is out to lunch..and they all are for the most part.
Some are stingy on the upper bands vs lower bands..and also vice- versa.
## Be careful with ants though. A Hygain 204BA is rated for 6 db. You will
typ see double that when pointed to EU..at least here from the
west coast. Wire dipoles dont rotate. Even a rotary dipole will show 14-18
db between the ends and broadside. Low dipole, oriented in the
wrong direction, vs high yagi pointed in the correct direction, is like night
and day.
## measuring audio levels with agc off, etc, is easy to do..and accurate.
This works good when somebody else is switching between 2 x ants.
Or the same thing with urself switching the ants.
Jim VE7RF
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