High Watts from mosfet DX979

[Tallman]

I think I've been misinformed about the capabilities of these radios. The dead key I'm seeing is around 8 watts with peaks up to 12 watts on AM. peaked and tweaked to maximum all frequency adjustments are in tolerance. It has two IRF520 fet's but only one in the final the other one is the driver. Am I missing something here? Do I need a special decoder ring to read the alignment instructions or a secret handshake?

Tallman

 

[Lil'Yeshua]

.

 

[Robb]

Check the gate voltage on the driver/final for 3.75v/ea just to be sure it is running up to snuff before any TX coil peaking.

 

[Lil'Yeshua]

Mosfet version:
Galaxy DX Radios DX979 (MOSFET Final) Service Manual

 

[unit_399]

If I'm not mistaken they only have one final. The other one is the audio amp.

The Audio Amp ??????? One IRF520 is the driver, the other is the final.

 

[Lil'Yeshua]

The Audio Amp ??????? One IRF520 is the driver, the other is the final.

Thanks for coming to the rescue to clear that up. I was working overnight and had only two hours sleep and couldn't take the time to give a clear answer.

 

[jessejamesdallas]

So you think it should be doing more watts or what?

I have a 979, and it swings little over 12w's...It's basically stock, with just a P&T from the shop it came from...

 

[Tallman]

So you think it should be doing more watts or what?

I have a 979, and it swings little over 12w's...It's basically stock, with just a P&T from the shop it came from...

From what I have read these 979's are easily tuned to put out 30 to 40 watt peaks with the single final. I have a dosey peak reading meter and I'm just not seeing what I expected from all of the reading.

The board that is in the 979 is also used in the 949, 959 and 10 meter Ham radios.

The Ham radio has twin finals and put out 40 watts dead key.

 

[binrat]

Not the same board. maybe the same design but a smaller board.

 

[Lil'Yeshua]

Do you have the modulation set at or near 100%? My 959 is DTB Radio tuned at 100% modulation. I have readjusted the deadkey to 6 watts. My Road Devil mic really makes the radio swing with a PEP of 43 watts with the RD volume turned all the way up but I keep the RD about halfway for the best modulation.

 

[Tallman]

Modulation

It is set at 95%. Should not make that much difference in the total peak.
I hate seeing the carrier pinched out all together. Radios that do that splatter like crazy.

 

[loosecannon]

Tallman,

on a PEP wattmeter, you should see about a 1 to 4 ratio of carrier to swing.

so, if your radio is deadkeying 8 watts, and you have the modulation set at 100%, then you should see about 32 watts of swing.

most likely you have mis-tuned the transmitter section during your alignment.

did you peak the coils using a modulated carrier? or did you tune them to "peak deadkey"?

my guess is that you tuned them using only a deadkey, which usually results in just what you are seeing.

try re-peaking the TX coils using a modulated carrier. (you can find a 1000hz tone on youtube, and just hold the mic up to a speaker)

also, the people that are seeing those numbers out of these radios are getting them by turning up the modulation pot past 100%.



Lil' yeshua, im a big DTB fan, and have always admired his work, but if you have a 6 watt deadkey and are seeing 43 watts of swing, then you are definitely over 100% modulation.
at 100% modulation you should see about 24 watts of swing.

LC

 

[Lil'Yeshua]

Thanks. I tend to Bragg. I remember in the past cranking VR16 up a notch but have turned it back since. Thanks to you guys I'm not trying to squeeze every single watt I can out of it but have gone for a good optimal performing rig. Plus the KL203 does the work now.

 

[loosecannon]

just so you know L Y, you cant really go by the position of the pot to set it at 100% modulation. its a pretty minute adjustment.
i do realize this is not a big deal, but i thought id mention it so you'll know in the future.
LC

 

[Lil'Yeshua]

I know. I recknecked the adjustment using my Redman modulation meter plus I know how DTB tuned it.