[TowerTalk] dx blaster antenna

Dan Zimmerman N3OX n3ox at n3ox.net
Thu Mar 5 08:28:46 PST 2009

> Anyway Im curious as to db gain vs s-unit. As I understant one S unit =
> aproximately 6 db however on my local repeater one gentleman is adimant that
> it's 3 db = 1 sunit. Im 95% sure it is 6=1s unit but when in slight doubt I
> confer with the wizards on tower talk.  :--}

There is no standard conversion from dB to S-unit.

On my FT-857D, I measured with a step attenuator and signal generator and
found something like this:

barely audible to S1 : lots of dB, don't remember how many, but way more
than 6dB
S1 - S2: 1dB
S2 - S3: 1dB
S3 - S4: 2dB
S4 - S5: 3dB
S5 - S6: 4dB
S6 - S7: 5dB
S7 - S8: 6dB
S8 - S9: 6dB
S9 - +10: actually 10dB, same for +20 and +30

Just on my rig, 1 S-unit can be anything from 1dB to 6dB.  It just doesn't
mean anything.

Measuring the rig's audio output voltage with the AGC off and the RF gain
turned down so the audio doesn't distort is a better way to compare

Another good method , but takes practice to do on the air is using a step
attenuator to check signal levels by attenuating everything to the SAME
S-unit reading (say, just barely S5), and comparing the difference in
required attenuation between the two things you're trying to measure.

S-units can be useful for quick checks, but you do need to actually know
what a S unit is on your particular radio.


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