DM780 / ALC Issue
I'm running the latest / greatest HRD / DM780 version with a RigBlaster PNP, Yaesu FT-817ND and an old Dell Inspiron 1000.
Per the '817 manual and general knowledge, you want at most 1-2 bars of ALC showing on transmit. I usually work the lower end of the 20m PSK31 watering hole, and I'll adjust the ALC level accordingly with the volume control on the PC.
However, if I move farther up the scale, the ALC level increases -- the farther I go up, the higher it gets. I have to reduce the audio level on the PC to correct it. This issue appears semi-linear in nature.
I'm thinking lower audio frequencies are suppressed somewhere between the PC and radio by some sort of isolation or filtering. Not sure if this is an issue with the RigBlaster, PC, software or the port on the radio.
Anyone else run across this?
On my Icom 718, the drive required for a certain power output changes allot depending on the band I'm on and where in the waterfall I try to transmit. So I would think it's normal. Some of it is due to the audio passband of the transmitter, and appearently on my radio at least some of the bands take less drive. I was allways told you should have no ALC indication. I can get 50 or more watts out of the 718 with no ALC indication at all.
Originally Posted by KF5FEI
I see the same thing with my 857, digipan, and a G3LIV interface. Unplug the radio and interface and listen to your own PC audio and see if there is a difference in the audio output low on the waterfall compared to higher up. I just did this on my Toshiba laptop and noticed some difference. There is a good chance it is very common
Originally Posted by KF5FEI
Radio works fine. I have made many contacts running the radio at full output and adjusting the ALC to 1-2 bars. This sets the actual output around 2-3 watts. Even worked France last weekend from north central Texas.
The only issue is with the ALC level increasing as I move up the waterfall -- the audio level is increasing as the audio frequency offset increases for some reason.
If you are using HRD to control the rig, you can use the center feature in DM780, it will put you in the middle of the waterfall. Look for "center frequency marker" in the options menu under waterfall.
Are you saying this will adjust the frequency of the radio so the QSO falls in the middle of the waterfall? If so, I can see where this might keep the ALC setting stable.
Originally Posted by WD0MYM
I use an MFJ audio DSP filter with customizable filtering. The one I use on PSK is centered on 1500 Hz, and about 100 Hz wide.
Hit the center in DM-780, switch in the filter, and work the weak ones.
Member: Backyard Engineering Group
I just did a test to with DM-780. a SignaLink USB and a FT-950.
I knew this happened when I ran digital on an Icom 718 then an Icom 7000. And it happens with the FT-950 also.
I set the Signalink TX level to give me 50 watts PEP carrier into a dummy load. I used 50 watts as it is easier to read my power meter when it is right on 50 watts.
I did this right in the middle of the waterfall, which reads 1500 on DM780.
When I went down to 200 on the waterfall scale the power dropped down to 45 watts PEP output.
When I went to 2900 on the waterfall the power really dropped off, down to 10 watts PEP.
I knew this happened. One day I seen a signal at the top of the waterfall scale and went up to work it. When I called I noticed my power level was way down and thought "oh oh, something is wrong"
This has been consistent on 3 rigs.
Now I have no reading on my ALC meter on the FT-950. I set the power out to 100 watts on the rig and adjust the SignaLink USB TX setting for my output.
If you are showing any ALC when transmitting near the bottom of the waterfall I can see how that ALC reading would increase if you went to the middle of the waterfall. Your rig will be putting out more power, hence your ALC reading will increase.
On my FT-950 I can produce 100 watts PEP into the dummy load on PSK31 and not see any ALC reading on the rig. Of course I never run that amount of power.
Using Olivia if I sneak the TX level up on the SignaLink to read 100 PEP on the watt meter I get 2 LED bars to light up on the FT-950 ALC meter.
So this ALC varies from mode to mode on my rig.
BTW, this change of power happens in every mode that DM780 offers.
All I know is this has happened with 3 different rigs so it must be a common issue.
Could be because when you operate near the top or bottom of the waterfall you are getting close to be out of the bandwidth of the frequency the rig is set on. Maybe the experts can weigh in on this matter.
Last edited by VE3FMC; 10-07-2010 at 11:06 AM.
Thanks for taking the time to do the test. I've got to sit down at the bench and hook up a scope and see if the audio level is changing from the PC, the RigBlaster or it is something with the radio.