[hpsdr] Mercury during transmit.

[Graham / KE9H]

David:

I totally agree with your analysis.

My mis-adventure keying 16 Watts into the front end for 30 seconds
resulted in D1 smoking and one of the internal diodes inside D1
failed, requiring its replacement.  No other damage to Mercury was
observed.  I absolutely don't recommend it for anyone's else's Mercury.

It was just an anecdotal report, to illustrate that the appearance of the
"overload light" does not indicate damage to the radio.  Damage occurs
at much, much higher levels.

I have another anecdotal report.  I just repaired a Mercury for Connie, N4GC
that reportedly took a "nearby" lightening hit.  D1 was cracked, and the 
leads
were discolored as if the tin had melted on the leads.  There was a black
"smoke ring" on the PC board surrounding D1.  Upon desoldering D1, it fell
apart into three pieces. It also turns out that the input low pass 
filter, FL1
had also shorted, resulting in very low sensitivity.  Upon replacing the 
parts,
his Mercury works normally.  No apparent damage to the relay, input 
attenuator,
the preamp IC or data converter.

--- Graham / KE9H

==

David McQuate wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Looking at Mercury's schematic and BOM, it seems that Mercury's 
> resistance to "high" applied power may be
> due to the bidirectional clamp diode, D1,  part number CBLC03C,
> but other components may nevertheless be at risk.
>
> The datasheet for D1 shows a graph of peak pulse power vs pulse 
> duration. Two points on the straight line of the log-log plot are
> 350W for 20 microseconds, and
>    35W for 2 milliseconds.
> Extrapolating to longer pulse duration,
> 3.5W for 200 milliseconds, and
> 0.35W for 20 seconds.
>
> The diodes start conducting (1 mA) at 4 volts, and clamping voltage 
> is  7 volts at 1A,
> or  19 volts at 20A (20 microsceonds max).
>
> At eight volts peak-to-peak at Mercury's input, D1 will be just barely 
> conducting.
> The input power from a 50 ohm source would be 160mW.
> If the 20dB attenuator is in the circuit ("preamp off") its input 
> resistor, R50, will absorb 99% of the
> incident power.  It is a 0603 size SMT resistor.  Typical power 
> ratings are 60 to 100 mW.
> So the limiting component seems to be the attenuator, unless it is 
> switched out.
>
> If the attenuator is out of the circuit ("preamp on"), the LTC6400-20 
> preamp will receive whatever
> power makes it past D1.  The preamp has its own built-in clamp diodes 
> connected to the +3.3v
> supply and ground.  These diodes are rated 10 mA max.  Input voltage 
> just slightly larger than 3.3 + 0.7,
> (that is,  +- 4 volts) will result in rms current larger than 10mA, 
> so, again, 160 mW seems the upper safe limit.
>
> While we have stories of survival at higher power, it seems to me 
> prudent to never apply more than
> 60 to 100 (maybe 160) mW.
>
> Other than relays, it might be possible to use transistors (BJT or 
> FET) or forward- and reverse-biased diodes
> to provide the needed protection.
>
> 73,
> Dave
> wa8ywq
>
>
>
>
>
> Richard Ames wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Mercury is reported to be a bit more rugged than implied below; see
>> http://openhpsdr.org/wiki/index.php?title=Mercury_-_Frequently_Asked_Questions 
>> and the references quoted.
>>
>> Of course the relays are still good / necessary.
>>
>> Regrds, Richard.
>>  
> _______________________________________________
> HPSDR Discussion List
> To post msg: hpsdr at openhpsdr.org
> Subscription help: 
> http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
> HPSDR web page: http://openhpsdr.org
> Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/
>


 1251764701.0