Below is the text of the description of the approach I use.
The block diagram is here:
https://groups.yahoo.com/neo/groups/apa ... 1997804010I have an ANAN-10E, which I use in conjunction with a 100W Elecraft KXPA100 solid state linear amplifier.
I have posted information on the Yahoo Groups Apache Labs web site regarding how I use Pure Signal without having to make any modifications to the ANAN-10E.
When transmitting, the "RX" SMA connector on the back of the ANAN-10E provides an input to the ANAN-10E's receiver...
even though the ANAN-10E's schematic shows that there is a relay (k19) that places a short to ground across the input of the ANAN-10E's receiver... on transmit. The reason is that, inside the ANAN-10E, there is a short length of 50 ohm coaxial mini cable between the input of the ANAN-10E's receiver and relay k19. The impedance... looking into the receiver end of this coaxial mini cable... is not 0 ohms when k19 is in the transmit position. It is actually (using a Smith chart to calculate the impedance of a shorted length of coaxial cable) about j5 ohms on 40 meters, j2.5 ohms on 75 meters, j10 ohms on 20 meters, etc.
I place an external 2 watt, non-inductive, 50-ohm resistor, located adjacent to the ANAN-10E's RX SMA connector, in series with the RX SMA input connector.
The result is, for example, on 40 meters: the impedance... looking into the added resistor that is connected in series with the SMA RX port... is very close to 50 ohms (resistive). I.e. 50 ohms + j5 ohms is approximately 50 ohms. In addition, the combination of the added 50 ohms of series resistance and the impedance looking directly into RX the SMA port (i.e. j5 ohms) forms a 20dB voltage divider [i.e. j5/(50+j5)] feeding into the receiver of the ANAN-10E on transmit.
In the case of my setup, I drive the input side of the added 50-ohm series resistor (located adjacent the ANAN10's RX SMA connector), using 50-ohm coaxial cable... with a 10:1 current transformer that is sampling the output of my 100W amplifier. The secondary of the current transformer has a fixed, 5W, 150 ohm, non-inductive resistor directly across it (for safety). Therefore, the parallel combination of that 150 ohm resistive load, and the 50 ohm resistive load looking into the coaxial cable that feeds the RX SMA input of the ANAN-10E, produces a total load across the secondary of the current transformer of 37.5 ohms. The voltage reduction between the output of the amplifier and the output of the current transformer is, therefore, (1/10) x 37.5 ohms/50 ohms = .075 = (approximately) 22.5dB.
The net voltage attenuation between the output of the amplifier and the input of the ANAN's receiver is (approximately) 22.5dB + 20dB = 42.5dB. That works fine with my 100W amplifier, for providing a proper feedback signal for Pure Signal. I.e. with this level of external feedback, Pure Signal sets the ANAN's internal adjustable receiver input attenuator to 17dB. The total voltage attenuation between the 100V peak RF output voltage of the amplifier, and the input to the ANAN receiver's RF preamplifier (including the attenuation of the ANAN's internal adjustable receiver input attenuator) is 42.5dB + 17dB = ~60dB. Therefore, the Pure Signal input voltage, to the receiver's RF preamplifier, has amplitude: 100mV peak. The ANAN receiver's RF preamplifier has a gain of 20dB... so the Pure Signal input voltage to the A/D converter = 10 X 100mV peak = 1V peak.
If you have a 1000 watt output amplifier chain, then you need an additional 10dB of attenuation in the feedback path. You might implement this by using 30 turns on the current transformer’s secondary, instead of 10 turns.
Also, if you are going to operate the transceiver + amplifier at frequencies above 14.3MHz (i.e. on 17m, 15, 12m, 10, and/or 6m), you will need to increase the attenuation between the amplifier’s output and the ANAN-10E’s RX SMA input… by adding an additional 10dB attenuator between the output from the current transformer’s secondary winding (which still has a 150 ohm resistor directly across the secondary winding, inside the box) and the 50 ohm resistor that has been added in series with the ANAN-10E’s RX SMA input. This can be accomplished with a symmetrical 50-ohm impedance, 10dB, pi-shaped resistive attenuator. [I.e. a 100-ohm non-inductive resistor for each leg of the pi, plus a 68-ohm non-inductive resistor for the top of the pi]
Stu