Why no analog ALC with the Flex?

W4AFK Bruno

I have two radios connected to a SPE Expert 1.3K FA amp. One is a TS-480SATt with the ALC line and the other is a FLEX-6400. I never had any issue with the TS-480SAT. The amp loves it and never tripped no matter what band or antenna.

However, with the FLEX, as there is no analog ALC line, you have to set the levels and drive level for each band. Many times the amp will trip on different bands and I have to lower the processor, level, etc. No consistency.

If the TS-480SAT and Expert work flawlessly, why doesn't the FLEX also have an analog ALC line so that it's all automatic?

Is it because complications if the ALC loop needs to go digital?

Just curious as an "old" analog radio works just fine with the amp while when using the FLEX, it's "touchy".

Erik Carling EI4KF

I have the 6400 and SPE 1.3 but not the trouble you report. I have an ALC line connected between the two using the ALC socket on the radio. I was not too sure if this was sufficient so I set the SPE per the 'ALC with Flexradio' section in the SPE user manual. End result is no over-driving, also a very clean signal it would appear. I do not see from the Flex ALC meter any instance of the amp indicating a need to reduce input, even at full output from the amp.

wp4oxg

Hi. An answer for your question is on this article:
https://helpdesk.flexradio.com/hc/en-us/articles/360040840731-Hardware-ALC-for-amplifier-protection-is-not-recommended-with-FlexRadio-SDRs-

Erik Carling EI4KF

That is not an answer, it is merely a point of view. One that is not shared by SPE. They clearly state in the 1.3 manual:

In this way the drive power from the exciter will be regulated automatically without having to set it. Plus it automatically adapts to your transceiver’s voltage range (e.g. any range between 0 volts and negative 12 volts. The use of the ALC port is highly recommended.

The bold text is their emphasis. They go to to detail what should be done when using a Flex radio as the exciter, which is obviously different to using transceivers with conventional ALC lines.

I have tried operating the SPE without ALC. It is pretty touchy and I am less than convinced that a clean signal from the amp is always guaranteed. Also, in this condition, mine will sometimes trip just as with Bruno. But if you, wp4oxg, are a SPE 1.3 user with a different experience then please let us know.

Perhaps nobody will agree with me but I personally believe this is a function of the SPE and not the Flex. Whilst I still have the SPE, I changed to Acom. They, like Flex, do not promote the use of the ALC connection and therefore I run that amp without. I have never had any problem with with over-driving when using the Acom with the Flex.

wp4oxg

Hi Eric. No I am not an SPE user. I was just pointing to the Flex discussion about the OP question "Is it because complications if the ALC loop needs to go digital?".

W4AFK Bruno

WP4XOG - Reason #2 is what I suspected.

The argument is that you have to convert the analog ALC to digital so that the software can handle it, which causes delays.

"Imagineering" - The driver and PA stages of the SDR radio is "analog", so why not add an analog ALC line and circuitry to these stages that would override the software ALC when an external amp w/ALC is used? What am I missing? This would react as fast as any traditional analog radio.

I have been using all sorts of HF amps since I became a ham and I always used the ALC line. We all know that the radio's efficiency can change over frequency so any preset level needs to be for each band, etc. For example, I don't need to worry that my TS-480SAT will overdrive the Expert 1.3K FA as the radio's output level is automatically reduced by the amp. Never had any overdrive issue, amp drop outs, etc.

Erik EI4KF - I read the same thing regarding ALC in the SPE Expert amp manual and I do use the ALC line with the TS-480SAT ... works like a charm and no distortion. With the Flex, I need to be very careful about the drive, audio, etc. or I trip the amp into bypass, even if you follow the instructions regarding setting the drive/power levels for each band (which is a pain in the "you know what")

Erik Carling EI4KF

Then you should liaise with Bob Hardie at Expert Linears because mine does not have that trouble and it was Gianfranco himself who told me to run ALC and set it up per the manual. And yes the per band and worse still the per band and per power level setting up is a tremendous PITA. I used to think the 1.3 was the bees knees but my Acom is superior.