K3 - Tx power in digi modes

[GW0ETF]

About to (finally) try out some RTTY/PSK31 using soundcard AFSK A/DATA A modes. Intuitively was going to run at reduced power being 100% duty cycle but have read in a couple of places (not the manual..) that you can run RTTY at full power (100w). Is this right and presumably it applies as well to PSK?

RYRYRY

Stewart Rolfe, GW0ETF

[Julian, G4ILO]

GW0ETF wrote

About to (finally) try out some RTTY/PSK31 using soundcard AFSK A/DATA A modes. Intuitively was going to run at reduced power being 100% duty cycle but have read in a couple of places (not the manual..) that you can run RTTY at full power (100w). Is this right and presumably it applies as well to PSK?

The K3 is rated for 100W key down for 10 minutes, Eric has actually stated this, so you should be OK to run RTTY at that power. Having said that, I've noted PA temperatures in the high 50s after shorter periods and about 50W power, so I personally wouldn't want to try it. But that's what the spec says. I'd certainly expect the fans to be going full blast at that power.

It really shouldn't be necessary to run PSK31 at such high power as most other stations use 20 - 40W. Having said that, I have inadvertently discovered (due to the power control issue discused at tedious length in other threads) that the IMD is not unacceptable at 100W peak. At that power level the K3 power meter will be showing 3 - 4 blobs while the signal is modulated. The problem currently is that you can easily overdrive the PA because the K3 can't be relied on to limit the power to 100W peak just because you've set 100W on the dial. So to be on the safe side - especially if you don't have a separate IMD meter to monitor your signal - I'd recommend aiming for no more than 50W peak, which should show about 20W average on a modulated PSK signal.

[Joe Subich, W4TV-4]

> About to (finally) try out some RTTY/PSK31 using soundcard
> AFSK A/DATA A modes. Intuitively was going to run at reduced
> power being 100% duty cycle but have read in a couple of
> places (not the manual..) that you can run RTTY at full power
> (100w).

The K3 will handle 100W for 10 minutes in ... RTTY will be
fine at full power.

> Is this right and presumably it applies as well to PSK?

PSK31/62/125 is a "two tone" mode and will show significant
IMD at power greater than 50 to 60 watts peak (20 to 30 W
average in "idle").

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of GW0ETF
> Sent: Tuesday, January 20, 2009 4:49 AM
> To: [hidden email]
> Subject: [Elecraft] K3 - Tx power in digi modes
>
>
>
> About to (finally) try out some RTTY/PSK31 using soundcard
> AFSK A/DATA A modes. Intuitively was going to run at reduced
> power being 100% duty cycle but have read in a couple of
> places (not the manual..) that you can run RTTY at full power
> (100w). Is this right and presumably it applies as well to PSK?
>
> RYRYRY
>
> Stewart Rolfe, GW0ETF
> --
> View this message in context:
> http://n2.nabble.com/K3---Tx-power-in-digi-modes-tp2185735p218

5735.html
Sent from the Elecraft mailing list archive at Nabble.com.

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Julian, G4ILO]

Joe Subich, W4TV-4 wrote

PSK31/62/125 is a "two tone" mode and will show significant
IMD at power greater than 50 to 60 watts peak (20 to 30 W
average in "idle").

Actually, as I said, it's quite acceptable at 100W peak, which I have run on several occasions inadvertently due to setting the power control to 40W and believing that's what I was getting.

Exceed 100W though, and it rapidly becomes awful.

It would still be a good idea to have some form of IMD monitoring in place if you are going to try higher power levels, though.

[Julian, G4ILO]

Julian, G4ILO wrote

Actually, as I said, it's quite acceptable at 100W peak, which I have run on several occasions inadvertently due to setting the power control to 40W and believing that's what I was getting.

I must apologize and correct the above statement since I was thinking about what happens when you use the QRP version of the K3. Although the QRP K3 radiates a signal that falls within the range KK7UQ defines as "good" ( < -23dB) at full power (10W), the IMD is unacceptable if the K3/100 is driven at full power (100W.) Apologies for the misinformation.

For what it's worth, this is the table of power output vs IMD measured by me on 10MHz (NB: Powers quoted are peak power. Average power during a modulated "idle" signal is about one third of this.)

 2W  -30dB
 4W  -30dB
 6W  -29dB
 8W  -27dB
10W  -24dB
12W  -22dB
above this point the PA kicks in:
20W  -28dB
40W  -26dB
above 40W the IMD cannot be regarded as "good":
50W  -23dB
60W  -22dB
80W  -21dB
100W -18dB