[1000mp] Mark V Field Power Output Mod

[Adam Farson]

Hi Mike,

Safety is not the issue with AM operation; the PEP of an AM signal at 100%
modulation is four times the resting carrier power. If the transmitter's
power budget limits PEP output to 100W (as it does in a "stock" radio), the
maximum AM resting-carrier output which can be achieved whilst maintaining
the correct sideband/carrier amplitude ratio is one-quarter of 100W, i.e.
25W. 

The following reference deals with the IC-756Pro/Pro2, but the principle is
the same.

http://www.qsl.net/ab4oj/icom/ic756pro_notes.html#am

If 25W is exceeded, the transmitter ALC will "rob" power from the carrier,
upsetting the carrier/sideband amplitude relationship and causing increased
distortion. As described in the reference, I was able to see this quite
clearly on the spectrum analyser.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: 1000mp-bounces at mailman.qth.net [mailto:1000mp-bounces at mailman.qth.net]
On Behalf Of Mike MacDonald
Sent: 02 August 2004 16:42
To: All about Yaesu 1000mp
Subject: RE: [1000mp] Mark V Field Power Output Mod

So what's the consensus of a safe level for AM? Seems like it may do more
than 25W.

Mike
WA2E

-----Original Message-----
From: 1000mp-bounces at mailman.qth.net
[mailto:1000mp-bounces at mailman.qth.net]On Behalf Of Thomas Giella KN4LF
Sent: Monday, August 02, 2004 6:28 PM
To: a Yaesu E-Group; a 1000MP QTH e-List; FT-1000MP at yahoogroups.com
Subject: [1000mp] Mark V Field Power Output Mod


Justin et all,

The Mark V Field power modification is simple but it will attract naysayers
that will warn of power supply damage/failure, finals failure, degraded
transmitted spectral purity, etc.

Pop the top and bottom covers. Gently turn the rig upside down on a hard
surface with the front of the rig facing you. There are three boards
visible. One is the "Control" board on the left side, the "AF" board on the
back right side and the "IF/Filter" board on the front right side. Go to
VR3003 on the AF board and turn it clockwise. It's marked "RF Power" (I
think it was). Fully clockwise gives you 190 watts in the CW mode on 14200
kc, 200 watts on 1845 kc and 180 watts on 28400 kc. Of course connect an
antenna with low VSWR or a good dummy load.

I've tested the rig extensively at 175 watts on CW and RTTY and have
suffered no component failures, overheating, etc. and no transmit spectral
degradation. Of course like all mods. make it at your own risk.

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