Separate RX antenna

Angel Andres

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Jun 26, 2021, 8:44:39 AM6/26/21

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Hi,

I would like to use the HL-2/N2ADR filter board with a separate RX antenna and a small amp for 80m in a local 10W CW contest. SO2V in PowerSDR being the main 'incentive' of this 'project'.

I have been looking at some of the previous posts on a separate RX antenna and schematics and if I have correctly understood, I could pick up the RX antenna on RF3 but I need to disconnect the RX path of the main RX/TX ant path/port.

I had a quick look at the PCB and schematic and I did not see a obvious way to to this. I will have another look at it. Has anyone gone down this path? How is this implemented?

My other options are to either use an external relay driven switch to commute the antennas on PTT or alternatively I could check if the the HL-2 low RF output has enough RF power to drive the amp to 10W and pick up the RX on the main antenna RX/TX port.

73 Angel

M0HDF

Steve Haynal

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Jun 26, 2021, 12:51:24 PM6/26/21

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Hi Angel,

You can remove J1 to disconnect the main RX path from the RX/TX TR. Also, if you external amp only requires a low drive level, you can use the low power TX output and then reserve the main antenna for RX only. There are other posts describing how some have used the extra bit on the N2ADR filter relay selection IC to control an external RX/TX relay.

73,

Steve

kf7o

wj.sz...@gmail.com

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Jun 27, 2021, 1:00:21 PM6/27/21

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Hi
Yes, controlling the relay with the control voltage at P13 (right next to the antenna socket) is a very good solution.
The buttons on the GUI assigned to the pin (point) P13 are:
Among others
"RX Antenna" at OpenHPSDR.
And "GP7" in SparkSDR.

73, Joe
LB1HI

Angel Andres

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Jun 28, 2021, 6:13:11 AM6/28/21

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Hi Joe and Steve,

Many thanks for the responses.

It is useful to know that the RX antenna control via P13 is available in the N2ADR board and switchable via software. I will see if I can find a suitable design to implement the TX/RX antenna commute box.

Using the 10W qrp-labs PA on the low power RF port seems also like an option for me as I have measured about 20dBm at max gain on my HL2.

73 Angel

M0HDF

Matthew

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Jun 28, 2021, 7:55:47 AM6/28/21

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There is a long thread on this here. Take care with hardware PTT and software PTT against your requirements/system. Make sure you observe the behaviour of GP7 (on a scope) to ensure it is suitable for your requirement with your chosen SDR software. It sounds like you might need some logic connected to PTT out and GP7 from the HL2.

73 Matthew M5EVT.

wj.sz...@gmail.com

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Jun 28, 2021, 8:15:26 AM6/28/21

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Hi again,

Very practical and simple.

For additional protection against possible software errors, we can use TX inhibit.

Then we are sure that HL2 will switch to TX state only when the antenna RX / TX switching has been successful.

73, Joe
LB1HI

Angel Andres

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Jun 28, 2021, 9:47:44 AM6/28/21

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Hi Matthew,

Thanks for the links and warning about the timing requirements on PTT sw / PTT hw and keying line to avoid any hot-switching/damage.

I currently use a RF front end limiter with the IC-7300 to avoid damage to the front end when using the RX antenna - which is in close proximity to the TX antenna.

I am planning to use a winkeyer with PTT to the ring and CW keying to the tip of the HL2 front panel connector. I know the HL2 will go into TX when the tip is just used but I am not that familiar with how cw is generated and the timing between PTT and key line in that case.

It looks like going down the path of using a small 10W qrp-labs PA on the low power RF1 connector will be a lot easier to implement.