Antenna Genius 8X2 power limitation on 50MHz

Pat W5VY · August 2023

Does anyone have an idea why the AG 8X2 switch has such a steep power de-rating on 6M? Normal Coaxial Relays have de-rating curves based on Frequency, Altitude, Temp, etc. A relay that handles 3KW on 28MHz would typically be good for 2KW or so on 50MHz. I just bought an AG 8X2 during the recent Flex "deal". I didn't notice the 800W limitation on 50MHz. Others have mentioned issues with high SWR on 6M with the AG in-line. I see port to port isolation in the specs. Any data on Insertion Loss on different bands and are some ports better that others for 50MHz? Any mods to overcome the 800W limit? I have a Flex 6700, PGXL, TGXL and like to chase 6M DX. Running 800W from the PGXL on 6M is going to be hard to take. The 800W limit should be displayed in RED in the sales literature....so I might notice it :)

Mike-VA3MW · August 2023

Pat

You might consider getting in touch with 4O3A directly, as they were the ones responsible for derating the switch. Let me share what 4O3A shared with us.

There have been instances where repairs revealed that customers were running over 1500 watts on FT8, which resulted in the switch failing and necessitated a new board due to the resulting damage.

4O3A also suggests performing a sweep of the switch on 50MHz to determine which configuration provides the lowest SWR on 6M. In my case with the version 1.0 switch, it was A3 and B6. For my 6M antenna on Antenna 6, I made sure to use this setting when operating at high power. This is your quickest work around.

To sweep your specific switch (as each one varies), you would need to connect a dummy load to each port and test the SWR – this can even be done using the radio. Just focusing on 6M would involve conducting 16 tests.

According to 4O3A, there isn't a straightforward modification available.

I've managed to achieve worldwide contacts using 750 watts on 6M (Canadian Legal Limit for digital modes).

Going up to 1500 watts only results in a 3dB increase, and due to the QSB on 6M, the impact isn't substantial (only half an S-Unit). While you're likely already aware of the logarithmic nature of power, I mention this for the benefit of others who might not be familiar with the concept.

Pat W5VY · August 2023

Mike,

Thanks for the response and info. I did submit an "info" ticket to 4O3A and got a quick response from Ranko. He acknowledge that long periods of 1500W FT8 on 6M will overheat the PCB. He said he does run 1500W for short periods of time but doesn't CQ for extended periods at that power level. RR on the less that 3db difference between 800W and 1500W. You should know better that to try to sell that logic to a DXer or VHF/UHF nut :) . I did some testing yesterday with my AG Plus 8X2. I used a VNA to check both SWR/Return Loss and Insertion loss. I only looked at Antenna Port 1 and 4 with Output A. SWR on Ant Port 1 was 1.19:1 and Ant Port 4 was 1.3:1. Insertion loss was about 0.06db at 50.313 on Antenna Port 1. I didn't check other antenna ports. I'll do that before I put it in service. I don't known the physical arrangement of the PCB(s) in the AG. Most likely on standoffs from the case. Don't know if securing the AG to a metal plate or using a small fan on the bottom of the case would help or not. A small fan circulating air through the switch would help but there may not be room? Future versions of the AG could include a temp sensor and send a warning to the Flex Radio to back off on the drive level.

73,

Pat, W5VY

Mike-VA3MW · August 2023

Thanks Pat. Nice update. I'm not sure just how the problem amplifies itself.

Antenna Genius 8X2 power limitation on 50MHz

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