From: "G4WGT - Gary" <g4wgt@talkgas.net>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 5 Feb 2004 21:43:08 -0000
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Subject: LF: RE:  G0MRF 300w Tx & DDS VFO
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Hello Jim & LF,

Thanks for the very useful data Jim, I did in fact get a reply from the
organiser of the kit/project & he has stated that several builders have
experienced the same low output & have diagnosed a faulty modamp, I have
doubly checked for the sort of error you suggest & that seems ok, also there
is some gain thro' the ERA-1SM. Now that I have some figures to refer to I
can have another look at the signal path etc. From memory I don't believe
that I am getting anywere near 250mV p-p from the DDS IC before any
amplification takes place.

I will let you know.

Thanks again

Gary - G4WGT

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of James Moritz
Sent: 05 February 2004 19:56
To: rsgb_lf_group@blacksheep.org
Subject: LF: RE: RE: G0MRF 300w Tx & DDS VFO


Dear Gary, LF Group,

There should be about 12-13dB of insertion GAIN between the DDS output
and the output of the PCB due to the ERA-1SM modamp. Looking at the
Analog Devices data sheet, and the schematic component values, the DDS
output should be 10mA pk-pk, driving roughly 2 50R loads in parallel,
i.e. 250mV pk-pk. The modamp should bring this up to about 1V pk-pk. The
DC bias voltage on the modamp output pin should be 3-4V. Is it possible
the modamp is in the wrong way round? If it had got turned through
90degrees, the signal would go straight from DDS to output via the 2
ground pins of the modamp.

Cheers, Jim Moritz
73 de M0BMU