Initially I set the output power on the power meter to 5mW (7dBm). I then hooked it up to the spectrum analyser At +7.8dBm at 28MHz from the XV port 2f was -24dBC, 3f was -20dBC. :-
I then backed off the output ~3dB to 5dBm and things improved dramatically. 2F was over -45dBC, 3F was -28dBC
The moral is; dont push the PA on the Hermes board and always use a 28Mhz LPF. To be safe the transverter was left set for 3dBm drive and an LPF will be built:-
2F is -48dBC, 3F is -32dBC. For the record PA gain is set for 43.0 in power SDR and the xverter output coupling was set to -19dB by choice of resistor values on the PCB (My hermes board came from TAPR which did not have the resistors or connector fitted for the transverter output). My setup was assembled shortly after ANAN-10 was launched. It used the Hermes board from TAPR and the PA board/Case from Apache-labs. The completely assembled version was on back order. The 3 antenna ports are left unterminated The TX port on the Hermes was terminated with 50 ohms as the board is still generating around 250mW when the transverter output is 2mW
I thought the Anan-10/Hermes transverter output was specified as 0dBm output? At that level what does 2fc and 3fc look like?
ReplyDeleteMike G8TIC mike@tubby.org
If you get the recent ANAN-10 version from Apache-labs it is 0dBm. Mine is a very early version where the Hermes board came from TAPR with no transverter components and the PA/Case came from Apache-labs. I chose -19dB coupling. No mention on Apache-Labs site as to what their coupling currently is. My 3dBm +19dB =+22dBm is below the Hermes output stage rated power.
ReplyDeleteFor the record I measured mine at 0dBm out 2F was -50dBc 3F was still -32dBc
It should be noted in the Hermes manual "Hermes_User_Manual_V1.17.pdf" by VK6APH. "Hermes is intended to be used with either a Power Amplifier, incorporating a Low Pass Filter (LPF), or an external LPF. The LPF should have 30 dB of attenuation at all harmonics of the transmit frequency. Do not connect Hermes to an antenna without incorporating a suitable LPF." This warning also applies to the XV output