[Lowfer] 600MRG> YAESU FT-757 GX-II Service Manual

[Dave Brown]

Andy
You will find that the receive performance, although unusually good 
compared to the LF performance of other rigs from the same era, falls 
away below 200 kHz but is still useful down to below 100 kHz.
I have performance test figures somewhere from when  I did some 
comparisons a few years back but not sure where they are just now.
 The transmitter is also unusual- if you have 'broadbanded' it, from 
memory it puts out near full power right down through a lot of the 
broadcast band!    At 500 kHz its starting to fall away and although 
you can still get a few tens of watts out of it, if you try for too 
much for too long, it shuts down to protect the finals from over 
heating as they are obviously running quite inefficiently down there.
IIRC below about 460 khz there's basically nothing useful coming out 
of the pa stage. There is quite  a sharp cutoff involved. The level 
out the transverter port drops away down below 500 kHz as well, but 
its low level anyway so another 6-10 db external gain is all thats 
required for 136 and 180 kHz. Again- IIRC!

A useful aspect is the band data output on the back- its not 
documented, but it changes at 1.8MHz from 0001 to 0000 for all 
frequencies below there- so you can use that for automatically 
switching LF gear or antennas in/out of cct etc.
The only issue with the 757GXii is that the rig is of the older type 
that does not lock all frequencies to a single reference. But its 
stability is not too shabby after a decent warmup period. And the use 
of sound card interfaces with external calibrators etc for BOTH TX and 
RX allow fairly good overall frequency accuracy.
73
 Dave, ZL3FJ

----- Original Message ----- 
From: "Andy - KU4XR" <ku4xr at yahoo.com>
To: "600 meter group" <SHMRG at piobaire.mines.uidaho.edu>; 
<lowfer at mailman.qth.net>
Sent: Sunday, May 30, 2010 5:57 PM
Subject: Re: [Lowfer] 600MRG> YAESU FT-757 GX-II Service Manual


A special thanks to David - N1EA for his help. He had the manual
supplement that covers alignment procedures for the FT-757 GX-II.
Now I can give this nice little rig some needed TLC, and get it
ready to use with my transverter. I was very pleased to discover
that the 757 GX-II has a low level RF transverter output jack
specifically made for that purpose. No need for attenuator
networks, or " TEE'd " off dummy loads for reduced power.
In the short time I have used the rig, basically today, I have
found it to be a nice performing rig so far. Almost on par with
my TS450S Kenwood. The receive on LF is pretty good, WWVB comes
in strong at 60 KHz, and the rig receives all the way down to
10 KHz. Another thing that surprised me was that it has a pre-amp
for receive, and it works at LF. It will bring signals at 100 KHz
up at least 2 S-Units when turned on. For the pre-amp to even
work at LF is a blessing. I'm looking forward to using this rig
in the days ahead.

I have never failed to get help when I need it from you gentlemen,
you are a great bunch of guys, and I'm glad to have gotten the
chance to know some of you. By email anyway.

73 to all, and GOD Bless you and your families :



Andy - KU4XR - EM75xr - Friendsville, TN. USA
LOWfer Beacon " XR " @ 185.29875 KHz ( QRSS-60 )
Coordinates:  N:  35º 43' 54" - W:  84º 3' 16"
http://www.myspace.com/beaconxr
http://webpages.charter.net/ku4xr/



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