[600MRG] Fwd: Re: Fwd: Re: Testing new Transmit downconverter

[Edward R Cole]

Pat,

At 09:49 AM 4/25/2013, pat bunn wrote:



>-------- Original Message --------
>Subject:        Re: [600MRG] Fwd: Re: Testing new Transmit downconverter
>Date:   Thu, 25 Apr 2013 13:46:00 -0400
>From:   pat bunn <pbunn at patbunn.com>
>To:     John Langridge <jlangridge at sbcglobal.net>
>
>
>
>For CW QSOs  a transverter is probably OK.  I have not heard of many HF
>rigs that stay stable within 1-2 Hz while transmitting for long periods.
>Most are stable enough for receiving.

I think too many folks think one has to run 100w into a 
transverter.  You only need about 10mw to drive a mixer and that will 
not result in thermal drift.  On 490-510 KHz I run my K3 at 0.1mw 
output.  The 10w amplifier is not engaged.  RF is output thru the 
low-level transverter interface at nominal 1mw.  I actually have to 
run at minimum to avoid overdriving the NDB transmitter which is 
serving as a very linear amp.  Since it sits 12-feet away from the K3 
there is no thermal effect from either the amplifier stages or the 
55v PS, thus the radio achieves the same freq. stability in Tx as it 
does in Rx which is 0.1ppm.  At 500-KHz this translates as +/- .05 
Hz.   If the K3 is run at 10-MHz into a transverter it can achieve 
1-Hz stability.  I will not comment about other radios as I do not 
own them, but I suspect if the transmit power stages are disabled 
then decent stability can be achieved.

If all you want to run is CW then the rest of what you wrote is 
fine.  But CW is limited in ability to work at weak signal 
levels.  That is why QRSS and other modes are used.  Some digital 
modes do not require linear amps, and some do.

73, Ed - KL7UW


>Easiest way to get on the band for non linear modes in my opinion is
>with a class D transmitter. A 12 volt rig in PP is an easy 110 watts
>that can be built for $35. All that you need to drive it is a CMOS level
>square wave. At 500 KHz, transmitters and power is cheap and easy.
>
>W1JR has a nice driver circuit that uses a 2X logic signal - I have also
>used the Microchip driver with a built in inverter that uses a 1X signal.
>
>I have found that if you use high voltage good FETs like the Fairchild
>FQA series rated at 200 -  400 volts at 40 amps or so, two will get an
>easy 500 watts and a pair will go to a KW. That is with a 50 -60 volt
>power supply. The Mean Well switchers are not expensive and make great
>fixed voltage power supplies at 48 volts.
>
>Just heat sink the FETs and a use  variable voltage supply to allow
>going from 100 to 1000 watts with four FETs that you can get for a
>couple $ each. Even at a KW they are over 90% efficient so the heat sink
>is well within an easy to get size.
>
>
>
>
>Pat
>N4LTA
>
>
>
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