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TX Delay & RCA TX1& HI SWR

I have had issues with HI SWR and the amp has been back to the factory for work. Recently I discovered and anomaly with the settings for TX Delay.

I operated SSB Sweepstakes high power, 800 contacts, with no issues. The amp was rock solid. In the subsequent week I made perhaps 100 FT8 contacts running 4-500 watts through the amp - again rock solid. I used power because of the HI SWR issues I had previously had with the amp and wanted to give it a good workout in digital. Last weekend I did CQWW CW, about 700 Qs and the amp drove me nuts. It appeared to randomly fault HI SWR. Sometime I would call a station ok and the amp would fault when I gave my exchange. Sometimes it would fault on initial call. I did very little running because the amp was so unpredictable. I finally swapped in my KPA500/KAT500 Sunday morning and had a smooth rest of the contest.

My HI SWR problem has only occurred on CW since I received the amp back from the factory.

I have a SteppIR and key the amp through the RCA connection so that the SteppIR controller can interrupt the key line if the tapes are moving.

I had set my TX Delay on the TX tab of Radio setup to 30 ms per the factory recommendation during the last troubleshooting session. The manual explicitly states that at least 10 ms are required when keying the PowerGenius. It also states that TX Delay is added to any setting for the RCA connectors. I don't think that is true. Yesterday I set a 30 ms delay on RCA1, which I am using to key the amp through the SteppIR controller, and my CW HI SWR problems appear to have disappeared. I put in about 350 contacts in the ARRL 160M contest Friday night with no SWR faults. Note this was on 160 with SteppIR controller turned off. In CQWW 160 faulted as much as the rest of the bands. Note I first checked this out on 17; it was rock solid with the RCA delay and intermittent with no RCA delay.

I think the documentation needs to be changed. It doesn't appear TS Delay is added to the RCA values. If keying a PowerGenius from an RCA connector the appropriate delay needs to be added to that connector on the TX tab.

Keith - AC9S


  • Dan-N7HQ
    Dan-N7HQ FlexRadio Employee, Community Manager admin
    edited March 2021

    Hello Keith,

    Which documentation version? If it is wrong, we will definitely correct it; thanks for pointing this out.

    The current PGXL manual uses 20ms for the recommended TX Delay value; it recently changed from a 10ms minimum with the latest firmware. Be sure to download and read the updated manual.

    I wrote about the TX Delay and PTT delay issue here:

    Using External Amplifiers with a FLEX-6000 Transceiver - Part 1 – FlexRadio

    Here is a summary of TX Delay:

    TX Delay defines the total amount of time between PTT depress and RF being sent out the antenna port to your amp. TX Delay is always set long enough to allow for safe switching. How long that is, depends on the amplifier and other switching requirements.

    The ACC/RCA TX output delays start with PTT, run and expire independently.

    Consider a 6-meter scenario, where you want to engage a relay that shuts off a preamp on a receiving antenna a few ms before it keys the amp. So you might connect the preamp bypass keying circuit to TX1 with a timing value of 0 and connect the amp PTT to TX2 with a value of 20ms.

    The TX Delay is set to 30ms here to allow 10ms for the amplifier to switch. In this scenario, once PTT is pressed, the preamp would shut off right away, the amplifier receives PTT signal 20ms later, and 10ms after that, the radio emits RF.


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