In message , Jerry Stuckle
writes
On 1/7/2014 2:29 AM, gregz wrote:
Jeff Liebermann wrote:
On Mon, 06 Jan 2014 23:23:56 -0500, Jerry Stuckle
wrote:

On 1/6/2014 11:04 PM, Jeff Liebermann wrote:
On Tue, 7 Jan 2014 03:19:54 +0000 (UTC), gregz
wrote:

Jerry Stuckle wrote:
On 1/6/2014 1:28 AM, gregz wrote:
wrote:
"only 3 db", but that's twice the signal. I have mine stacked 12 feet,
but I believe Winegard says either 8 or 10 feet. Mine work
swell. +:^] I
got mine just after they were discontinued in 2005/6. Had to email a
number of suppliers until I found the second one. I bet there are some
still in storage somewhere, email different places that sell Winegard,
you may still find one.
John K9RZZ

Twice the signal means twice the voltage, for me.
Greg

Twice the voltage is a 6 db gain. Twice the power is a 3db gain.

Exactly. If I got 1 microvolt, 2 microvolts will be twice the signal.
Greg

Sorta. If you got 1 microvolt, 2 microvolts will be twice the signal
voltage but only 1.414 times the signal power. That's why we have
units of measure to avoid such ambiguities. Just to be difficult,
working with antennas, the "signal" is the field strength measured in
dBuV/M. If you define what you're measuring and specify your units of
measure, you wouldn't be having such problems.

You've got it backwards, Jeff. Twice the voltage is 4 times the power.
1.414 times the voltage would be twice the power.

Very embarrassing. Temporary loss of IQ from working on my broken car
with a cold or flu this afternoon. It should be:
If you got 1 microvolt, 2 microvolts will be twice the signal
voltage but 4 times the signal power.

Thanks for the correction (grumble)... Maybe if I go to sleep early,
when I wake up tomorrow, this didn't happen.


I have not really been specifying units. I was just going over the
situation in my mind, and I straightened out in rf terms.

I got this going out terminology. IF, in audio, I got two speakers
transmitting equal energy, with two amps or channels, and I receive that
totally in phase, I got twice the signal or 6 dB power increase. I've
measured it. It's true. Same thing would happen with two antennas with two
transmitters. Two antennas, one transmitter, with one splitter would only
give 3 dB power increase at the receiver. I'm just thinking out loud. I had
to ease my mind. I think I'm ok now. Almost bedtime.

Greg


No, two in-phase speakers provide 3db increase, not 6db.

If you could double the signal and get 4x the power you could make
gazillions! Of course, you'd be creating energy out of nothing, but
who cares about the laws of physics?

Two identical receiving antennas would provide twice the signal voltage
if their RF outputs were connected in series.

One way of doing this would be for coax feed from each antenna to be
connected to the primary of a 1:1 RF transformer, and the secondaries of
the two transformers were connected in series. So if each antenna
delivered 1V from a resistive source impedance (R) of 1 ohm into a
matched resistive load of 1 ohm, the two secondaries in series would
provide 2V. However, the output impedance of the two secondaries would
be twice that of each antenna, ie 2R. To preserve matching, the load
would also have to be 2R.

However, the snag is.....
The matched power from each antenna is 1V squared divided by 1 ohm
(=1W), but the matched power from the combined antennas is 2V squared
divided by 2 ohms (=2W) - which is an increase of 3dB (and not 6dB).

Of course, if the receiver input was not matched, and its impedance was
much higher than R or 2R, it might be possible to benefit from adding
the two antenna signals in this way. Has anybody tried this?
--
Ian