IO board and Pure Signal

[Craig Honeyfield]

I have installed the IO board into my new Hermes Lite 2 and am wondering what is needed to get the pure signal jack operating correctly.  Is any PICO software needed?  If so, what particular software?  When I look at the GIT repo, I really just saw some software that tests the board, but nothing that I could see that controls pure signal.  I'm running Thetis.  I can write my own python script if needed to set the registers correctly, but I have a feeling most people installing this board would likely want at least Pure Signal to work with some type of default software install.

Thanks

Craig - N6MUD

[James Ahlstrom]

The Pico software in n2adr_basic/build/main.uf2 is a good start and you can use it for pure signal.

You don't need your own Python script. You can use software/n2adr_ioboard.pyw.

Thetis and other SDR software should have a setting for register REG_RF_INPUTS and the default zero is probably what you want.

Jim

N2ADR

[Craig Honeyfield]

Thanks Jim.  Reid, does Thetis HL2-Beta6 have any support for the new I/O Board?  

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[Reid Campbell]

Yes, Beta 6 supports the following I/O Board functionality:

External Rx input
Pure Signal input
Rx/Tx antenna selection - As far as I know, there is no support in the current Pico code to implement the switching of relays but support for the protocol register is in Beta 6.

Cheers

Reid
Gi8TME/Mi0BOT

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[Pez]

There was talk previously (before the IO board existed) in the group about improving PS on the HL2 by reducing crosstalk (to achieve 'close' to Anan levels of IMD performance) . It was suggested that by implementing an additional relay(s) to disable part of the RX input on TX, that the PS signal would be more pure, with less internal crosstalk, resulting in a much better PS result (lower IMD). 

My first questions is, does the new IO board provide this hardware functionality to improve the PS performance, over that of the standard RF3 direct connection method? If so, does the  n2adr_ioboard.pyw script do this? 

My second question: does the IO board provide any impedance matching or buffering to remove the RX loading issue we see when using RF3 in the 'traditional' way for PS? (This is around 3dB of reduced RX signal when RF3 is fed with a 50 ohms sample, and closer to 1.5dB when fed with a higher impedance around 300 ohms). 

Thanks all.  73

[James Ahlstrom]

Hello Pez and Group,

The IO board provides switching between RF2 on the HL2 board and J9 (aux Rx input) on the IO board. It does this by switching the T/R relay to Tx so that RF2 is not in the Rx path, and by connecting J9 to RF3. This makes J9 and RF3 an unloaded Rx input independent of RF2.

If REG_RF_INPUTS is zero, the HL2 operates as usual and J9 is not the Rx input. Pure signal input J10 can be used to inject a signal into RF3 as usual. This works, but will not result in an improvement in crosstalk.

If REG_RF_INPUTS is one, J9 is the Rx input and the pure signal input is not available.

If REG_RF_INPUTS is two, J9 is the Rx input if the HL2 is in Rx. If the HL2 is in Tx, then the pure signal input J10 is switched to RF3 through an attenuator and J9 is switched out. Although this reduces crosstalk from J9 it will not reduce crosstalk that occurs on the HL2 board. Someone should measure whether there is an improvement. 

I am guessing that most crosstalk comes from having a 5 watt power amp on the same board as the Rx input. This can be reduced by using the highest possible level of pure signal input and a minimum level of RF gain during transmit. If this is not adequate, then the low power output from the HL2 can be used with an external 5 watt amplifier.

Jim

N2ADR

[Craig Honeyfield]

Hi Reid,

I noticed when using the new I/O Board and pure signal, the Theits A-ATT value when transmitting is only "6".  When using by other Hermes without the I/O board with the sma jumper coax soldered onto the header pins, it has a much higher ATT value of 22.  Everything is the same, (sampler, amp etc) but just different Hermes.  Is this expected?  I am concerned that with a low value of 6, it's not a strong enough signal for pure signal to work correctly with my amp.

Thanks,

Craig

N6MUD

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From: herme...@googlegroups.com <herme...@googlegroups.com> on behalf of Reid Campbell <scumballc...@gmail.com>
Sent: Sunday, September 24, 2023 2:44 PM
To: herme...@googlegroups.com <herme...@googlegroups.com>
Subject: Re: IO board and Pure Signal

 

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[Reid Campbell]

Hi Craig,

The I/O Board has it's own attenuator on it which looks like it would give about a 13dB reduction in signal over a direct connection HL2.

Thetis will adjust the A-ATT value to get the feedback in the correct range for the PS to work correctly and this should be signified by the PS indicators going green.

Cheers 

Reid
Gi8TME/Mi0BOT

[d b]

Greetings!

Newbie here (geez.....again?!). What is the minimum and maximum RF input level in dBm for the IO board PURE input that feeds the Hermes input RF3 (looking at the schematic I see a 51-ohm terminating resistor on the IO board input, so I assume 50-ohms input)? I will eventually build an external RF sample to feed this input for amplifier pre-distortion correction.

Assuming an external 100w RF amp, maybe something around a 25dB attenuating sample?

Many thanks!

Dan

W1DAN

[Duncan Clark]

You need one of these:

https://sites.google.com/view/vk1hw/homebrew/taps/rf-sampler

I used a Fair-Rite FT82A-43

It will work fine for Pure Signal from a few watts to 1000W.

With 15W a few hours ago in Thetis I was seeing something like 13dB attenuation and a green Pure Signal indication level of around 147, if memory serves me corrrectly. It was working fine with 1kW as well.

Duncan