Hi Andrei,
I am not quite sure what you would like, so let me see if I understand you. It would seem that you would like the PA-100D to be capable of being controlled from the Elad FDM-DUO both for transmit/receive switching, as well as automatic band selection. That being the case there are two possibilities here. (Fortunately I have an Elad FDM-DUO, so I can experiment.)
1. HARDWARE
To switch the amplifier into transmit, it is only necessary to ground the T/R line on the rear panel. On the rear panel of the Elad FDM-DUO there is a 3.5mm PTT-OUT socket. By connecting a 3.5mm to 3.5mm lead between the ELAD PTT-OUT socket and the PA-100D T/R socket will cause the PA-100D to go into TRANSMIT whenever the ELAD FDM-DUO goes into TRANSMIT.
IMPORTANT NOTE The PA-100D repeats the PTT input signal on the ring connection of the stereo plug, and as the ELAD FDM-DUO uses the ring connection internally, you will need to make a special lead that uses a 3.5mm stereo plug at each end but only connects the tip to tip connection and the screen to screen connection. Failure to heed this warning might damage either the ELAD or the PA-100D. Also, DO NOT USE A MONO PLUG AND LEAD! This will damage the amplifier and the Elad FDM-DUO! Note also that in order to ensure that the amplifier has completed switching, to give time for the relays in the PA-100D to settle, you will need to set the PTT Delay in the ELAD FDM-DUO to something other than the default of 0mSec, and I would start with 50mSec, and work downward.
2. AUTOMATIC BAND SELECTION
The PA-100D can be set to use the Frequency Sense mode of operation whereby it measures the frequency of the RF drive signal, and selects the appropriate band. Alternatively, if you connect the accessory Elad SERIAl I/O adaptor you can use the Yaesu-compatible band voltage available on this adaptor, or you can use the RS-232 port and communicate via the ASCII protocol. In this case, set the PA-100D mode to the KX3 setting, and this uses exactly the same command sequences for band selection as the ELAD FDM-DUO.
3. FIRMWARE
The PA-100D already uses the ASCII command protocol, and as the ELAD FDM-DUO responds to this, the standard frequency query command ( FA; ) from the PA-100D will cause the ELAD FDM-DUO to respond with its VFO-A frequency in the format: FA00012345678; for example to indicate a frequency of 12345678Hz, or 12.345678MHz. This is exactly the same as many other transceivers including the Elecraft KX3, so setting the RS-232 mode of the PA-100D to the KX3 mode will allow correct operation.
Consequently, even as it stands, without any hardware or firmware modifications, and without using the ELAD Serial Interface, the PA-100D will work perfectly well with the ELAD FDM-DUO. If you wish to use the serial port to communicate with the amplifier then you can do this one of two ways. The first is via the ELAD Serial I/O adaptor which gives you a RS-232 serial port but only operating at 38.4KBaud, nevertheless the PA-100D firmware can accommodate this speed. The second way, with which I have been experimenting lately, is to build a 'reverse USB Host' interface, and connect this to the rear panel B CAT socket on the ELAD FDM-DUO. This will then allow you to operate at any serial speed. If you contact me via my email address I can give you further details. My email is:
adrian04@cytanet.com.cyHopefully I have answered your query.
Regards,
Adrian, 5B4AIY