Flexradio 1500 interfaced with MX-P50M

VA3NTI

Hi I am wondering if I interface the MX-P50M linear amplifier to the Flex 1500 do I need to add this https://www.ebay.ca/itm/Amplifier-keying-relay-buffer-amateur-radio-interface-RBI-1-switching-250-SOLD/140456018374 relay buffer between the radio and the amp? Or do I just make a DB9 cable using pin 1 for ground and pin 3 for PTT out from the flex connector that is in back of the radio?

Hope this makes sense but can not found anything on the net to answer my questions.

Dudley WA5QPZ

The amp keying is performed by a solid state device, rated at 50 volts at 50 milliamperes, should key most modern amps, BUT its a good ideal to use an external keying relay to better isolate the radio from any noise or transients that might come back down the amp keying line. I personally always had a external relay and have not had any keying issues with 5000, 3000 or 1500.

73

Dudley, WA5QPZ

VA3NTI

Thank you very much Dudley for answering my question. I really appreciate it. I will look into the external relay.

2E0PJY

I have ordered an MX-P50M waiting patiently for it to find its way to the UK from China! In the meantime I have been researching PTT switching options and came across the solution below that uses a widely available MOSFET and a couple of resistors. I have built it and plan to use it with my Flex1500 and MX-P50M. Thought I would share it in case its of any use to anyone!

WX7Y

I really don’t think the Little amp your looking at will key with much more current then the Keying circuit you are looking at.

If the amp is built for a modern day radio like the FT817 then it will work with the Flex1500, KX3 etc radios with no problems.

The FT1500 uses a FET on the key port if I remember right which is rated by FLEX in the owners manual to handle 250MA and 30 Volts which is probably FAR more then the little MX-P50M AMP needs to key your looking at.

WX7Y

2E0PJY

Agreed, although I built the cable as above in my previous post and its working perfectly I guess although not really necessary it cant do any harm. Only seem to to be able to get about 35 watts out of it though, my 1500 doesn't seem to generate 5 watts at full drive, I can get about 4 watts on full drive with FM.. Not sure why!

WX7Y

excellent glad it worked for you

WX7Y

excellent glad it worked for you

WX7Y

excellent glad it worked for you