Max continuous power FT817ND

[VK3LU]

I currently use an FT817ND on WSPR running 1 watt on HF. Does anyone know what is the safest power output that can be run on WSPR? (2 minute continuous carrier)
I would like to run more than 1 watt but am scared of damaging the rig. I would imagine that 3 watts could be the limit but who knows?

Nev

[VK4ADC]

Nev

Watch the video at https://www.youtube.com/watch?v=zqtH8i7HtP0 as it mentions how to get away with higher power out without cooking it.

The user manual says 1.5W on AM so that is probably do-able on digital anyway.

The other thought is a small linear kit eg DIY kits 70W SSB linear HF Power Amplifier For YAESU FT-817 KX3 C4-003 D9Z4
from eBay and just throttle it way back.  You may need to add LPF sections after it too.

(https://www.ebay.com.au/itm/DIY-kits-70W...SwzxZdLpEZ)

Doug

[VK3LU]

Hi Doug,
I asked the question because I couldn't find the rig's manual.
So out of curiosity I looked at the specs for my IC7300 for continuous carrier operation and found that it is rated at 100w for fm and 25 for am. Hmmm.
Then I finally found the FT817ND's manual and it states 5w for fm and 1.5 for am.
Why the difference for two continuous modes? Perhaps the finals are operating in different classes. 
I have seen those amp kits you mentioned but they don't supply heatsinks and as you said LPFs would have to be built and switched for each band.
If I went down that path I would probably go for the MX-P50M. 

Nev

[VK4ADC]

5W for FM - yep, VHF PA
1.5W AM - yep, HF PA.

Without looking at the block diagram or schematic, I think I would be right about the above.  

Find yourself an old CPU heatsink, cut & file to size and voila..

[VK3LU]

The manual doesn't say that Doug.
No bands are specified, just overall power outputs versus modes.
I have to take the manual as gospel, otherwise it has no credibility.
Perhaps others have more info.

Nev

[VK4ADC]

Nev

You are right : This is from the Tech Supplement for the 817ND :-

Power Amplifier Circuit
The transmit signal from the MAIN Unit arrives at connector J3001 on the PA Unit. The transmit signal (1.8 MHz to 430 MHz) delivered to the PA Unit is amplified by pre-driver Q3001 (2SC3357), driver Q3002 (2SK2596) and final amplifiers Q5401/ Q5402 (2SK2975: Lot 1 - 74, RD07MVS1: Lot 75 -).

Low-Pass Filter (LPF) Circuit
The transmission signal from the power amplifier circuit is passed through a low-pass filter which consist mainly of RL3001-RL3015, RL3017, and corresponding inductor and capacitor networks. The LPF is a 5th or 7th-order Chebyschev type filter, utilizing nine different sections for the various amateur bands at 1.8 ~ 430 MHz.

So it is just the ONE PA stage from 1.8 through 430 MHz. A little different from what I have seen in other models but I guess space really is at a premium in the 817 series radios.

In some ways it makes it easier for you - just one physical area to add an external heatsink for regardless of band used.

A small image of the PA block area is below...

   

[VK3LU]

Doug.
Interesting design. Being such low power probably makes it easy to do that.
I think I shall keep the power to no more than 3 watts on wspr for safety's sake.
I don't fancy having to replace the finals

Cheers
Nev

[VK5ZD]

25 watts AM = 100 watts PEP at 100% modulation. i.e. same PEP.

[VK3LU]

Thanks 5ZD
I should have remembered that.
Too many birthdays I think!

Nev

[VK6ZFG]

My FT817 with added Heatsink

Igor
VK6ZFG

[VK3LU]

Hi Igor,
That looks like good insurance.
How effective is it and was it easy to fit?

Nev

[VK6ZFG]

Hi Igor,
That looks like good insurance.
How effective is it and was it easy to fit?

Nev

Hi Nev

Real easy to install. 

Uses two recycled TO-220 PCB heatsinks of the type that are soldered in vertically onto PCBs by two pins (pins removed).  Heatsinks held in place with thin double sided outdoor tape (what I had on hand).  Proper thermal tape probably better.  Need the tape to allow for the raised lettering on the FT817 case.  

Seems to be working according to tests with an infrared thermometer.

73s

Igor