The AM Forum

Moving along on the 813 transmitter project here (pair modulating a pair, ala K1JJ et al)....
Before I start drilling the pi network/output tank deck I need a sanity check on component ratings.

Target operation is 2000v, 250mA, 500w input, 375w output, and so a 4000 ohm plate load and Class C.

I have Tonne's PI-EL design software, which will calculate Vpk and Arms for each tank component, but I need to enter the PEAK PLATE SWING.  For CW or unmodulated carrier I presume this is just 2000v ?   But what do I enter for PEAK PLATE SWING under 100% modulation?   Is it 4000v?


Thanks, Steve   

RMS Plate or Vrms = sqrt(4000ohmsX375Watts) = 1,225Vrms or 1,732Vpeak

Power at 100% Modulation = 1.5X375Watts resting carrier = 562.5Watts

Vrms = sqrt(4,000ohmsX562.5Watts) = 1,500Vrms or 2,121Vpeak

Minimum DC blocking/RF Coupling cap value should be >> 2,000Vdc+2,121Vp RF or ~ 7.5 kV.

How is Tonne defining "Peak Plate Swing?"

Phil

Thanks Phil.  That is helpful.

Tonne supplies the attached diagram for peak plate swing, but I guess you'd have to derive the value using tube graphs and formulas.

I think the peak DC plate voltage would be twice the DC supply voltage with 100% plate modulation.  I also think the RF peak voltage would be 4 times the DC plate voltage.  Been a while since I looked at all this so I might be wrong.

Fred

If you experiment with the Tonne software, you’ll find that doubling the plate volts doubles the RF voltage.  At 100% modulation, plate voltage is doubled.  So is current.  Whatever it says for carrier, double the numbers and those will be the 100% modulated numbers…

Ed

I've used Jim's software before.  Works out pretty good, just need to account for strays.

I used the G3SEK spreadsheet more.  It allows for more granular input of strays, etc.

Both good, get you where you need to be.

The G3SEK spreadsheet needs a spreadsheet installed.  Cool thing is, Google sheets works fine, so it will run on the phone!

--Shane
WP2ASS / ex KD6VXI