I have at least one preliminary number for power consumption.  I have the PA, drivers, and DC-DC part of the APT circuit running now.  I can get about 2W (with two 1W signals) average power out of it.  It draws about 6W to do this and does get a bit warm.  This is for running at that power continuously.

73,
Dan W9EQ

On Tue, Jun 16, 2020 at 1:49 PM Marc Franco via LTM <ltm@amsat.org> wrote:
I couldn’t agree more, John.

73, Marc N2UO



On Jun 16, 2020, at 1:21 PM, John Klingelhoeffer via LTM <ltm@amsat.org> wrote:


Yeah, it really isn't worth the effort for 2 or 3 dB more.  

If one had the power and heat dissipation capability for +40 dBm (10 dB more) , now you're talking.  

Yes, it could probably fit on the QSH/QTH stack, though.  Heat dissipation would be an issue. 

73

John...
WB4LNM


On Mon, Jun 15, 2020 at 11:04 PM Eric Skoog via LTM <ltm@amsat.org> wrote:
The latest version of the LTM's RX/TX card that Dan is finishing up has two RF output power levels:  500 mW and 1W.  When he's through testing, I've asked Dan to provide me with the DC power consumption numbers for all the possible modes (TLM only, Transponder Only, TLM + Transponder ----- for High and Low power settings).  We know Linear Amplifiers are NOT very power efficient.  So I'm expecting this high power mode will require in excess of 3W DC..............we'll see.

As for adding an external amplifier to the 'stack', as JK asked, what is the final RF power level desired? Config-wise one could certainly connect the existing TX coax from the RX/TX card to a stack-mounted amplifier card and control it via QTH/QSH bus signals.  But the design requirements would have to be specified and there would be several design challenges and trade-offs.  I mentioned DC power consumption for low efficiency linear PAs.  Beyond that I would be concerned about RFI effects on other cards in the stack, particularly experiments.  Also, heat dissipation is a real challenge were the requirement to be several watts of RF, i.e., thermal issues. Lastly, I'd be concerned re meeting IM levels, i.e., spectral purity requirements from the ITU regulations. 

eric

On Mon, Jun 15, 2020 at 4:32 PM Jerry Buxton via LTM <ltm@amsat.org> wrote:
Quick question, what is the max power out can we get from LTM-1 and is
there a possibility of adding an "external amplifier" to the stack? 
e.g. fits on QTH/QSH bus maybe and input is just the output of the
transponder, picture your rig and the amp in your shack.  No power
supply considerations, just raw what if for the transponder.  Thanks!

--
Jerry Buxton, NØJY
Vice President - Engineering
Radio Amateur Satellite Corp.
(AMSAT)

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