Aussichten zu einem neuem Hermes Board, New Hermes 2M Board
Wie könnte das neue Hermes-Board aussehen?
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As Apache Labs has decided to stop the production of the Hermes board, we have discussed to see if it is possible to get it produced by others.
I have for a long time thought of the possibility to improve the construction and include some long wanted features. I am going to describe the modifications I am thinking on. And of course we are open for other ideas!
We have got all the original layout files for Hermes from Abhi and that is a good starting point.
Endre Kiss, YO6OGJ is going to do the layout job. The first he is going to do is to draw completely new schematics in Altium Designer. The physical layout of the new board will follow the original as near as possible to be sure that the good performance of Hermes is kept or even improved.
The preliminary list of modifications follows:
1: New PA giving 5W PEP output. By increasing the power output it can be used to drive a LDMOS PA directly to >1KW output. I have tested 2 of the newest 14V LDMOS transistors from NXP (Freescale) and they can give >5W linear output, also on 50 MHz. With Pure Signal, the IM3 is >70 dBc at 5W.
Even at 145 MHz, the power out is >1W with good linearity.
2: After a suggestion by Leif Aasbrink, SM5BSZ the DAC is going to give full output all the time and the drive regulation to the PA is done by using a step attenuator after the first low noise amplifier. This will keep the phase noise as low as possible in the TX signal. The same solution is going to be used in Metis.
3:Use the newest SMPSU chips for the power supply. The latest chips are much more „silent“ than the old and it is easier to suppress the spurs. By using one for the 5V bus and one for 3,3V and run synchronously, we need only 2 or 3 linear regulators in addition for the most critical systems so the total power consumption can be reduced. It might also be possible to use only one switcher delivering 3,3V. There are only a few circuits that use 5V so just a small linear regulator is needed.
4: Remove the ON/OFF switch from the board. In most systems the switch is on another board or installed on the front separately. And we can use the space for other parts.
- Add 2 meter operation on Hermes 2M by using under sampling. By installing
the 145 MHz BP filters on the bottom side of the board, the switching from HF to VHF should not introduce any extra spurs.
Including 70 MHz has been asked for but the restricted space forbids this.
And the chances to get extra spurs would increase.
As the new PA can give >1W even on 145 MHz, also TX is included.
6 New FPGA. Phil, VK6PH is looking for a more modern FPGA to replace the Cyclone III that is used today.
7: There is a need for some more I/O´s. For ex. control output for use with EER-PWM Power Amplifiers, interface to control an external ATU (compatible with ICOM ATU)and so on.
We are open for other ideas so please give feedback.
The decision to start a production will be taken after the schematics are completed and the cost is calculated.
A few prototype boards has to be produced and tested and eventually modified.
When the construction is tested and found OK, we can make a list and produce fully populated and tested boards. Also bare boards will be offered for the brave ones.
We also plan to make prototypes of a new Apollo board with 30W PEP out, also on 50 MHz and offer ready made boards without the inductors installed.
At the moment there are no plans to make complete transceivers. But combining Hermes 2M with Apollo and the PiHPSDR controller, a complete transceiver like the one I showed at Friedrichshafen last summer is possible.
We hope there are enough people that are interested in this. When I read the reflectors, my impression is that there still are a lot of people interesting in building their own equipment.