Using The Flex 1500 With RF Sensed Transverters Such As The Spectrum

I set up the transverter form on the Flex 1500 and chose to use PA to drive the Spectrum. To begin with all went well. However, after a while the PA failed to key on transmit.

Initially I thought this was down to a Flex PowerSDR quirk, you sometimes get glitches as the software is continually in development. A reboot and all seemed well. Unfortunately after a few minutes use, flicking to beacons etc. it repeated the fault.

A search online revealed I was not alone:

I spent a long time trying to figure out what what going on. If I set the radio up and left it alone it happily transmitted all day. At this time I was using an unmodified Spectrum. It drifted quite a lot so it was necessary to check against GB3BUX regularly and adjust the transverter form to bring it back on frequency. Once I did this I noticed the PA refused to key.

 I emailed Flex and received a reply:

'The XVTR menu is intended for use with the XVTR/com and XVTR/TX ports only, low level.    It does not have a provision for TXing through the PA and utilize the XVTR menu,  check your XVTR ports, I think that you will find it working there... 


I wasn't really satisfied with this answer. Flex advertise the 1500 as: ' The Perfect IF Deck for VHF-Microwave Transverters.'

I knew the PA drive worked fine via the transverter form so long as I left it alone. I tried various things until I found a repeatable set of actions which stopped the PA. It turned out it was the stack memory. So long as I didn't use it things were fine. Annoying, but not really a problem as the standard memory form worked fine.

I emailed Jim, GM4FVM, and he confirmed he had given up using the stack memory. He thought there was an issue with filter settings. This made sense. I emailed Flex back with the news but received no acknowledgement. Perhaps they do not wish to be held responsible for people blowing transverters via the PA.

In short, if you wish to use an RF sensed transverter, or one that requires watts (rather than 0dbm) to drive it. DO NOT USE THE FLEX 1500 STACK MEMORY. The standard memory form works just fine.

Use this at your own risk.

It has worked fine for me ever since.