Flex 6400 not keying Elecraft KPA-1500

Mike-N1VE

The two were working well until the amp stopped being keyed by the radio. I have the PTT on the amp connected to TX1 on the radio and the cable between the USB on the radio and the amp. The amp turns on and the display appears normal. When I key the mic, the radio transmits but the TX light does not show on the amp. and there is no indication of transmit power.

If there is a setting in the radio menu, I cannot find it. I am using the Maestro.

KD0RC

Hi Mike, Open the Maestro main menu, and select TX Band Settings. Make sure that the bands of interest have the RCA TX1 box checked. Look at section 33 of the Maestro manual for more detail. Also make sure that the cable from TX1 to PTT of the amp is OK and securely seated at both ends.

Mike-VA3MW

this video should help

https://www.flexradio.com/videos/how-to-connect-my-hf-amplifier/

Mike-N1VE

Len,

Thank you for your quick reply. I don't remember dealing with the TX band settings when I first set up the radio and amplifier, yet the radio and amplifier worked well together.

I changed the TX Band Settings by checking the bands that I use. I checked the RCA cable between the TX1 on the radio and the KEY IN on the amplifier. The cable is continuous on both the center and outside connection and not continuous between the inside and outside. Connections appear to be tight at both the radio and amplifier.

When keying the mic when the amp is in the operate mode, I get the message "RF IN, NO KEY IN".

Mike-N1VE

I substituted the IC-7300 for the Flex, including the RCA cable for the PTT, and the amplifier works fine with the IC-7300.

Perhaps someone could tell me exactly what I need for settings on the Flex to get it to key the amplifier. The Flex operates fine without the amplifier.

Mike-VA3MW

Hi Mike

All the steps are explained in the video with the use of TX1. Can you share a picture of your TX Band settings?

Mike

Mike-N1VE

Mike

I am still going through the video. Here are the TX band settings. I don't remember doing anything to any settings when I first set up the Flex to excite the amp. Perhaps my memory is faulty.

Mike

Geoff AB6BT

RCA TX1 boxes are not checked

KD0RC

Hi Mike, un-check the RCA TX Req boxes and check the RCA TX1 boxes and you should be in business.

Mike-VA3MW

RCA TX1, 2 and 3 correspond to the TX 1-3 on the back of the radio. As others have said, you will need to have the RCA cable plugged into TX1 and then also turn on the checkboxes under RCA TX1 for all the bands that you want to use the amp on.

Mike-N1VE

Mike,

Thanks for your continued interest in my Flex to amplifier problem.

I looked at the video and I think I understand most of what needs to be done to get the Flex to operate with the KPA-1500.

I now have the TX Profile set up properly. I have the RCA cable plugged into the TX1 port on the Flex and the other end of the RCA cable plugged into the "KEY IN" jack on the amplifier. The Elecraft KXUSB cable with the 3.5mm plug connected to the upper USB port on the Flex and the receiver serial port on the Electraft.

I know that there is a connection between the Flex and the Elecraft, because when I key the mic I get as message on the Elecraft "RF IN, NO KY IN"

I also set the TX Profile for RX2 and move the RCA plug to the RX2 jack. Same results...the radio does not key the amplifier.

Here is a photo of the Transmit section of the menu in the Maestro. This varies from the example in the video.

Mike

Mike-VA3MW

RCA cable to RX2? I am not sure what connector that is.

The RCA cable must be plugged into this connector for your amplifier. It is TX1 and then you must select TX1 as described above. Make sure you uncheck the RCA TX Req boxes since you are not using TX REQ.

If you like, try TX2 and then check the TX2 boxes in the TX Band Settings.

In the TX Delay box, from the picture you posted, please add 20 which will give the amplifier 20ms before RF is sent to the amplifier.

I used a KPA500 for years on my Flex6600, so I know this does work. As a simple test, you can short out the RCA connector going to the KPA500 to make sure it will go into TX. This is a simple and safe test to make sure the RCA cable you are using is functional.

It has been so long since I used the KPA500, but don't you have to make sure the KPA500 is in an autosense mode for the band you are on?

Mike-N1VE

"RCA cable to RX2? I am not sure what connector that is". My mistake I should have typed TX2.

The RCA cable is connected between TX1 on the Flex and KEY IN on the KPA-1500.

I changed the setting on the Transmit RCA TX1 to 20.

Here is a photo of the TX Band Settings.

Shorting the end of the RCA cable to the amp does not cause the amp to respond in any way.

The amplifier works fine with the IC-7300, using the cable that I just shorted.

I had been running the Flex for more than three years as an exciter for the KPA-1500, until it intermittently stopped keying the amp. Recently it stopped keying the amp altogether.

Mike-N1VE

Mike,

I just discovered that when I short the RCA plug from the amplifier, the amplifier TX light turns on.

The voltage from the amp at the RCA plug is 4.96 V, the center pin is (+)

I hope this helps.

Mike

Geoff AB6BT

Just reading the mail...

First you said this:

Shorting the end of the RCA cable to the amp does not cause the amp to respond in any way.

And then this:

I just discovered that when I short the RCA plug from the amplifier, the amplifier TX light turns on.

These two statements seem conflicting, can you clarify?

Mike-N1VE

When I first checked the amp by shorting out the RCA plug to the amp, I was looking at the lights on the amp that show that it is transmitting. They didn't light (no RF of course). The second time I checked I looked at the transmit light and it lit up.

Geoff AB6BT

So is it working now with the Flex? Sorry, still confused...

Mike-N1VE

No it is not working with the Flex, but it is working with the IC-7300.

Mike-VA3MW

If you have 100% confirmed that the RCA cable short test works 100% of the time (bad cable?) that is a good data point.

I would recommend you open a support ticket to have them follow up with further testing. I have yet to see a TX1 port go bad, but it is possible.

BTW, if you have not reset the radio yet, you might want to try that as well.

Mike-N1VE

The RCA cable short test works every time. I am using the IC-7300 to operate the amp with the RCA cable.

Is is necessary to have the cable between the USB accessory socket on the Flex and the XCVR SERIAL port on the Elecraft connected to key the amp? I ask because it appears that the 3.5mm socket on the amp is not making a firm (tight) connection with the 3.5mm plug in the cable.

I reset the radio before I made my initial contact with the Community.

I will open a ticket.

Thanks for your help.

JasonSt

I'm wondering what the end result is. I'm about to hook up my KPA500 and my KAT500 to my flex-6600... I'll watch the video and then see how it goes.

Mike-VA3MW

This explains how it functions

https://www.youtube.com/live/3_bSfOxi1sI?si=yJ8v79JIvhwKz2w3