[DSP-10] CW transmit has a raspy sound

[Lee Scott - AA1YN]

At 12:04 PM 3/29/2006 -0800, you wrote:
>Hi Lee,
>
>I was hoping Bob might check in here again. The output stage U106 seems to 
>be running saturated or very close to saturated. Maybe this is OK. I don't 
>think the mixer cares if the power is 5 DB too high.
>mar-4, 8.3 dbg, 1 db comp 12.5dbm
>
>I wonder about the first stage, U105. It drives the F_in of the 
>synthesizer (U104,pin8) as well as the output stage.
>
>mar-6, 20 dbg, 1 db comp +2 dbm,
>
>Working backwards through the numbers it seems the mar-4 would have to be 
>driven by +4.2 dbm (2 db above the one db compression level) from the 
>mar-6. For the mar-6 to put out that much power it would have to be 
>seriously overdriven or biased for a lot of current.
>
>This doesn't seem correct. I'll have to read through the original article 
>and see if there was any mention of drive and signal levels.
>
>There were a bunch of MAR-6 that found their way into the amateur 
>community that are pretty hot. Something else to wonder about.
>
>73 Mike KD7TS
>_______________________________________________

This AM I lifted the input pin of U105 and placed the coax pigtail on the 
junction of C119 and U105.

I measured the output of the J310 osc with an HP 435B power meter.  It is 
-3.0dBm into a 50 ohm load.  I then took a photo of the SA and it is quite 
noisy.  Actually it is worse than the amplified output of U106. I had to 
increase the scan width to 10KHz/div.

Bob,

What is the designed power level of the J310 osc? If given an output of 
U106 to be +7dBm, then the output of U105 should be -1dBm and the output of 
the osc should be -21dBm given the MAR-4 has an 8dB gain and the MAR-6 has 
a 20dB gain.

Is my measurement procedure upsetting the J310 by placing a coax on the 
circuit in place of U105?

Does the ratio of C117 and C118 control the output power of the J310?

Mike,
The TUF-1 would have no problems with a +12dBm level as it is designed for 
up to +17dBm on the LO input. The RF input is only spec'd at +10dBm.

I've got quite a few of those hot MAR-6 type devices and found they work 
best with about 30 to 40 ma of current. I forget what they had for gain. 
Seems to me they were hot like the MC devices.

I am positive about the value of C119 being 3.3pf as I had a friend double 
checking my work.

I think it is time for me to build a J310 osc on a PC board and start 
playing with it.




Lee Scott - AA1YN http://www.aa1yn.com
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