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.