Tony & Alberto
What about paralleling the unused switches in the '3126, since you are only using to in the new configuration?
Cecil - WA6RDY
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----- Original Message -----
From: "Alberto I2PHD" <i2phd@...>
To: <softrock40@...>
Sent: Monday, October 17, 2005 10:11 AM
Subject: Re: [softrock40] Two switch QSD test
Tony Parks wrote:
Hi Alberto,
The switches used are two of the switches in a FST3126. I am needing to
stay with this part for the v5.0 SoftRock to use a large supply of the
parts
I had to buy as part of a minimum order.
Would a lower on resistance improve the performance of a QSD circuit?
Hi Tony,
the RdsOn is practically in series with the 50 ohm of the antenna or
the output impedance of a preceding preamplifier. So for the maximum of
efficiency you want to keep the switch resistance as low as possible.
The FST3125 is rated for an RdsOn of 4 ohm, while the ADG704 (or the
ADG711 if you prefer 4 separate switches instead of a mux) is rated
for 2.5 ohm. Of course if you design your preamplifier with a somewhat
higher output impedance, then the issue is much less relevant...
73 Alberto I2PHD
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