HPSDR external amp ALC help

[VE7 Kilohertz]

Hi Guys,

My Penelope HPSDR system is on the way and am going to use my Collins HF-8020 with it. It only needs 100mW in for full out and I want to be safe and use the ALC voltage from the Collins to control the Penelope 500mW output. Tom Vu, how did your FT1000D conversion turn out? Is is still running 2 year later? I have a question for your setup. Did you find a way in incorporate ALC from the PA to the Penelope?

Thoughts anyone using HPSDR and an external amp? ALC would be nice.

Paul
Kilohertz

[W2JBL]

NEVER use ALC on AM- it will limit your positive peaks and cause the carrier level to shift under modulation, causing very undesireable affects to your audio. ALC is also a bad idea for SSB, as it causes splatter. best to use good audio limiting and compression to keep things under control. ever hear a station on SSB with nice full wideband audio and then tune off to the side and hear buckshot and splatter for 10KC each side of him? that's what happens when you hit the ALC on almost every modern radio including SDR radios, which are actualy the worst offenders when improperly adjusted.

[K1JJ]

Hi Guys,

 Tom Vu, how did your FT1000D conversion turn out? Is is still running 2 year later? I have a question for your setup. Did you find a way in incorporate ALC from the PA to the Penelope?

Thoughts anyone using HPSDR and an external amp? ALC would be nice.

Paul
Kilohertz

Hi Paul,

What 1000D conversion do you mean, the 200W amp carcass I converted for HPSDR use?  If so, then I decided not to use it cuz it is only about -31dB 3rd order, and I'm trying for better with the 4CX-350FJ IPA.  We'll know how it works out soon.

As for the ALC, I agree with Chris.  The problem with most ALC circuits is they are too slow and the attack time not fast enough to prevent the first part of the voice peak from flat topping for an instant. If you listen up the band, you won't hear constant splatter, but instead hear a short pop on the peaks as the ALC grabs hold. The delay might be in the diode detector at the transmitter pickup or in the circuitry in the exciter.  Maybe the HPSDR and Collins is faster and works well, I dunno. But this is the first thing you shud look at when hooked up. Schottky diodes may help.

The only reason I wud have ALC these days is for failsafe protection. ie, I would adjust it so it's never working unless I make a mistake and hit the amplifier with too much RF drive. This will fold back the pulse and protect your amplifer.  As Chris said, there are better (and cleaner) ways to increase your average audio level.

T

[VE7 Kilohertz]

Mmmmmm. Okay, thank you buys. An almost certain f aux pa averted. Well that makes things a lot easier.

Yes Tom, I was referring to your 2011 FT100D project, using the carcass. It sounded like a good idea.

I also discovered that there is a safety built in ALC, which is adjustable;e, built into the HF-8020, as well as TGC and IGC. Transmitter and Internal GC of sorts. The fail safe "shut things down" if someone manages to screw things up externally. As I was playing with it today into a dummy load, I could see the ALC action on the watt meter. At 400W carrier when modulating the power would cycle with modulation downward to about 200W. When I backed down the carrier to about 200W, nothing would happen on the power meter, just hung at 200W. The meter started to move when the carrier was at about 275W, so that is the magic point for this amp,

Anyway, thank you for setting me straight. I gave it a good run tonight on 160M and it worked 100%.

Cheers

Paul

[ke7trp]

Thats a good point about using ALC for protection.  Very important on some easy to FUBAR Tubes.  Depending on how the AlC is used it can really help throttle the radio back down, during tune up.   

I think the key is to not rely on the ALC action heavily.   I have mine set at a hard 1500 watts pep.  But rarely ever use over 1000 watts.  So the ALC never does anything unless, I mistune the amp, Or forget and leave the radio at 100 watt setting (the amp needs 50 or less for full output).

I find most hams dont use ALC. I think its a good thing if setup correctly.

C