Flex-5000 on the 630m band

The MW 630m band from 472khz to 479khz (just below the AM broadcast band)
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Flex-5000 on the 630m band

Post by ke9ns »

I found out the reason why some Flex-5000 radios will not output below the 160m band and some Flex-5000 radios will.

The original schematic (HTRX board) for the 5000 claims a LPF for 160m in the Transmit section of the circuit (Between K16-K17).
This is the LPF's before the PA Drivers.

If your Flex-5000 is older and has not gone in for service, it will have the original LPF design for 160m and 80m. So it will also Transmit on 630m

If your Flex-5000 is newer or has gone in for service, its likely it has the ECO (engineering change order) where Flex removed the original 160m LPF and put in a 160m band pass filter. This was to eliminate spurs. And so it will not transmit on 630m

When I opened up my 5000 I found that Flexradio had modified the 5000 by removing the original 160m LPF parts from the HTRX board, and replaced it with a Daughter board (PC-0054 Rev A) between the K16-K17 points.

This very small PC-0054 RevA board is a "Passive 4 pole LC bandpass Filter" Using my NanoVNA, it is a bandpass that allows transmit from 1.4mhz to 2.4mhz, but not only cuts off the higher frequencies but the lower as well.

I un-soldered the 3 connect points on the daughter board. I then replaced the original Inductor 3.9uH, and 3 caps (1800pf,1800pf, and 180pf) to put it back to the original LPF

Now the PA of the 5000 differs from the 3000 slightly. The 3000 has a slightly different 13.8v feedback transformer design, but I dont think that will effect 630m operation

Creator of PowerSDR KE9NS v2.8, based on the Flex Radio PowerSDR v2.7.2 software.
Flex-5000, LDMOS and Titan Amps, G5RV, and Mosley TA-33 Junior
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