Sunday, July 26, 2009

TX gate

I was visiting the Flex Edge site this morning. The Flex Edge site is a new discussion board over at the Flex web site devoted to cutting edge discussion about new features. Here was one post I was greeted with from W2RF.

W2RF is one of the unstoppable innovators and one of the drivers of the ever improving Flex CW experience so I was pleasantly surprised with his newly modified gate function in the audio chain

Here is his post

I've modified the TX gate in PowerSDR so that is
more like a downward expander, instead of a hard gate.
There is a new "Amplitude" control on the Setup
Transmit tab that sets how deep the gate will close.
It should produce a more natural sound when gating
out room noises such as air conditioners
and fans.

It is in branch w2rf/downexpand/bin/release

Let me know of questions or comments.

73 Ed W2RF

And here is Tim's W4TME's reply

Thanks Ed for this new feature. A downward expander
(DE) is something that I have been wanting for a
loooooong time as part of the TX audio processing
chain in PowerSDR. I never have liked the way
gates sound for voice applications due to the
"binary" nature of the way they operate.

I just finished some initial tests of this new
feature from Ed and I like it. Some will ask,
what is a downward expander?

The function of a good downward expander
is to increase the apparent dynamic range
of the system by decreasing the gain during
the relatively quiet times thereby moving
the apparent noise floor downward. It does
this by comparing the signal level to a
threshold. When the signal level drops
below this threshold, the downward expander
*decreases* the system gain by some ratio.
A noise gate (GATE) on the other hand does
not decrease the gain but switches it
completely off below the threshold level.
A noise gate is a DE at it's most extreme
setting where the slope (ratio) is infinite.

With the old GATE function, it worked best
if there was not a lot of strong ambient
background noise or the intensity of the
background noise was mostly constant. If
the background sound levels were close to
your voice level or the intensity of the
background noise was not constant, you
could not achieve "good gating" between
words or worse, your threshold setting
would be so sensitive that you would
experience a "pumping" effect of the gate
opening and closing in rapid succession
while you were talking.

The DE provides what is known as a
"soft knee" where the transition from
closed to open isn't so abrupt (off/on)
so that the "pumping" is no longer a problem.

So how do you use it?

For those who have used hardware based DEs
previously, this one works a bit differently
but the end result is the same. The DE
implementation uses a fixed slope or ratio
for determining the gain reduction after
threshold point (the place where the gate
closes and gain is reduced to zero). Now
there is an Attenuate percentage value
being applied to the "gate" function.

If the attenuate percentage is set for 100%
you have the classic GATE function
(all off/all on). Any percentage between
99 and 1 results in the gating action being
more like a downward expander. A attenuate
percentage value of 0% there is no gate or
DE function at all. Essentially the
Gate/DE is turned off.

My preliminary testing using the monitor
shows that the Attenuate percentage value
will be dependent on the back ground noise.
I have found that rather than setting the
threshold exactly at the point where the
background noise closes the gate, that
I can set the threshold at a more positive
value (smaller negative number on the PowerSDR
console) and use an attenuation percentage of
about 80% to provide that "soft knee" transition
(YMMV). So now if I open the "gate" with a
breath sound, the pumping effect is mitigated
by the DE. I really like this new capability.

I'll be doing some over the air testing shortly.

Please others out there try this out and provide
feedback to Ed. Hopefully this can get incorporated
into the SVN test branch.

All we need now is a de-esser" to go with the DE,
Compander, Leveler and EQ and we will have all
of the capabilities of a high-end audio channel
strip in PowerSDR making it THE premier phone rig


TMF (too much fun)


Saturday, July 18, 2009

2 RX's and power

There has been a recent thread on one of the lists I frequent. Every one is all worried if they run full duplex are they going to burn out their receivers.

I run this all the time with no problem, but that's not good enough. So I took the following shot

The setup for this shot is RX1 is connected to a 1/2 wave end fed vertical tuned for 40M. The TX chain is through a AL80B to this 1/2 wave antenna.

The second RX is connected to a full size 1/4 wave vertical on 40M. The antennas are located about 100ft apart in my back yard. Both antennas have good radial systems under them and are very efficient antennas.

In the picture you can see my power output in the WATT screen of DDUTIL at the bottom. I am running 1089.3 watts into my transmit antenna. The watt meter is a LP-100 that has been calibrated to a NTS standard. The above picture is what is seen in the second RX during transmission.

This second shot is of a picture of the radio immediately following transmission. The wattmeter has some persistence so this shot is in the RX mode just after my transmission. As you can clearly see both RX's are working just fine. I happen to have this particular amp in line tonight which gives me 10db of gain. I have other amps that can supply 15dB of gain on these same antennas and my experience is the same.

If I take the second RX antenna and run it through a second LP-100 into a 50 ohm dummy load, using the field strength setting in the LP-100 I measure 20.5 dBm for the 1100W. I have previously measured 22+ dBm using this setup at 1500W. That means RX 2 is experiencing +20.5 dBm on its antenna from all sources. Notice the S meter on RX 2 clamps at +9 dBm, which is where the elements protecting the front end kick on and do their protection. I reach +9 dBm at about 15W, and the radio stays at +9 dBm as I increase my power out on the transmitter.

Here is a shot I made of the radio just before it starts to distort

If the input goes to +8 dBm you will see distortion products start to form in the second RX

I'm basically using the transmitter as a high gain signal generator for the second RX. +7 dBm for a signal that is in the pass band of the receiver IS A PRETTY FRIGGIN STRONG RADIO, in case any one is keeping score. Note most tests are done with the offending signal OUTSIDE the pass band of the radio. blocked by roofing filters and all that crap. This +7 dBm is on the exact frequency the transmitter is set to not a KHZ or two down the band

I am publishing this just to document my experience. I am not suggesting any one else run their radio like I do. I have no fear that with the power I can generate of burning out my radio. If I was running 408 three phase at the primary of the amp power supply and 3 1/8 inch heliax I might feel differently

As one can see from the above data the radio is well designed for full duplex operation up through legal limit power.

If others have an interest and can take some screen shots, I would be willing to publish other experiences running full duplex at high power to further document this aspect of the radio.


Friday, July 10, 2009

More Diversity

Things have been a little quiet on the SDR front and the bands have been lousy. Behind the scenes WIBR is being fine tuned in the "test" branch of the SVN, and diversity is moving ahead.

Above is the latest "polar" control for the diversity project. The control allows you to adjust phase and gain between 2 antennas and 2 receivers in the F5K. Here is a shot of the F5K with diversity active

This morning I was on early playing with the diversity feature. I used the controls to null the band noise. Below is a recording of a very weak CW station. As I click the diversity off and on, you can hear the band noise reduced in a way that takes the station from about a R-3 to R-5. I didn't have a lot of time to explore this as I was transcoding the file and loading it up to my server before I had to scoot, but I thought the demonstration dramatic enough to warrant a little display.

Noise Reduction

Sorry for the low audio you will probably need some cans to truly hear the difference. This station was at the noise about -119 on 40M. My diversity set up on 40 is a 65 ft end fed half wave antenna and a 45 ft vertical that is tuned remotely at its base. Both antennas are very close in output and seperated by about 180ft or 3/2 wave on 40. The signals are pretty independent since you can see very different AGC action on the panadapter of the 2 receivers.

Eventually tuning this feature will be automated. Its an interesting evolution to witness.