On May 14, 2007, at 11:48 AM, Scott Manthe wrote:
One reason is called the inverse square law.
I'm familiar with that.
There's a HUGE difference in a rig being able to deal with a
kilowatt signal a couple blocks away and being able to deal with a
kilowatt signal in the same room.
I'm aware of that, too.
However, I wasn't talking about a kW a couple of blocks away. I was
talking about 100 watts in the same box, or 1.5 kW inside a 100m
circle (tops!).
At a M/M station with more than 6 rigs, you'll have two radios on the
SAME band, using antennas that are just a few dozen meters from each
other.
Another is that almost everyone who doesn't want to destroy their
rig's front-end uses giant bandpass filters in front of each rig in
a SO2R setup.
First, this isn't true. You don't need huge bandpass filters for an
SO2R setup. A typical 1.5 kW SO2R station will use a set of receive
filters or stubs to reject out-of-band signals. For 100w SO2R, you
don't need to have the filters.
Second, in the M/M comparison, you have two rigs on the SAME band, so
bandpass filters don't do you any good.
At NQ4I's M/M many of the second rigs don't use a bandpass filter at
all (although he has them available -- I know, I built one set for
him). They won't help with the in-band signals from the primary rig,
although they are useful for getting rid of mixing products from the
other five transmitting stations on the other bands....
Including eleven of these filters to cover all the bands the K3
will cover would make it the size of a broadcast transmitter.
You don't need it.
For reference for the HF challenged, take a look at a good set of
repeater duplexers. Now, multiply that by eleven bands.
You don't need filters the size of repeater duplexers to do this.
It's one thing for a 2 meter/440 rig to be able to transmit and RX
at the same time- they're running maybe 50 watts at 300 mHz
spacing. It's not so easy with a rig running 100 watts, a kilowatt,
or at some stations, several kilowatts at 2 or 3 mHz spacing.
At NQ4I, with antenna separation of just a few dozen meters, we can
often receive effectively within 10 kHz of the primary station.
--
Let's put it this way -- many SO2R stations use the Top-Ten A/B
switches to separate their antennas for two rigs: http://www.qth.com/
topten/abss.htm
These switches only offer 80 dB of isolation.
The Array Solutions SixPac has similar specifications: http://
www.arraysolutions.com/Products/sixpak.htm
About 80 dB of isolation below 30 MHz. The web page indicates you
should worry more about the coupling between antennas than the
isolation of the switch.
So, if 80 dB of isolation is sufficient for 1.5 kW signals, then 100
W signals would need 12 dB less, or only 68 dB to achieve the same
level of received signal in the second receiver. Call it only 70 dB.
That seems achievable. I don't understand why that couldn't be
achieved in a box the size of the K3.
Bill Coleman, AA4LR, PP-ASEL Mail: [EMAIL PROTECTED]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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