[Yaesu] FT-1000MP First Impressions on 160

[Bill Tippett]

K3MM wrote:

>No, the spot tone is not derived from the carrier...I dont remember reading
>that anywhere.

I haven't checked the schematic itself but the following was on page 42
of Yaesu's "Technical Overview" brochure:

"SPOT KEY:
The CW [SPOT] key activates the "Spotting" oscillator, which provides
the operator with an audio tone which matches--precisely--the pitch 
of the transceiver's (offset) CW transmitted note.  In operation, zero-
beating to an incoming signal is easily accomplished by pressing the
[SPOT] switch, then adjusting the FT-1000MP's receiver frequency so that
the tone of the other station's signal matches the Spot tone.  THIS 
TONE IS A LOW-LEVEL SAMPLING OF THE ACTUAL RF SIGNAL (my CAPS), not a
separately generated audio oscillator which could become mis-aligned, so
perfect alignment is always possible.  The pitch of the tone (and the
FT-1000MP's transmitted carrier) may be adjusted by using the PITCH
control."

However SPOT is being generated, it has bad distortion which makes it
difficult to zero beat.  As N6TV suggested, MONItoring the sidetone
when transmitting works much better but that is what SPOT should be
doing if the above were correct, and if it had low distortion.  And
besides, it's not real convenient to be adjusting RF PWR to minimum
each time you want to accurately spot using MONI instead of SPOT.

K3MM wrote:

>You guys need to spend some time noseing around in the MP manual for a few
>minutes.  It's all described on page 30 of the manual, with a block diagram
>of what is occuring.

Tyler, I read the same schematic but it does not explain to me what I'm
hearing with my ears.  The brochure mentioned above says the following
about the Low-Band Preamplifier on page 9:

"This preamp, optimized for operation in 1.8-7.5 MHz, features low noise
figure but low gain, along with extra selectivity for improved strong-
signal handling capability.  This preamp utilizes a single JFET in a
source-follower configuration."

It continues, after describing all preamp selections:

"For low-band operation, where input preamplification often is not needed,
the input RF preamp stage may be bypassed completely by pressing the
"IPO" key on the front panel, which provides direct feed to the first
mixer without the addition of any stage gain.  This has the practical
effect of increasing the system noise figure by approximately 7 dB,
while improving the 3rd order intercept by approximately 12 dB."

My question is:

If low-band preamp gain is very low (zero to my ears), what advantage
does it offer over just selecting "IPO bypass" (schematic on p30 of the
manual)?  Is it more selectivity which may not be apparent in casual
listening.  If it is MORE selective than IPO Bypass, would the 3rd order
intercept be improved by even more than 12 dB?  I'm not a receiver
designer...I'm just trying to understand what is going on, whether my
radio is working correctly, and how I should use it to maximum advantage.
If I had some test equipment here I could answer my own question very
quickly.  (For anyone trying to follow this discussion, you MUST refer
to the schematic on page 30 of the Operating Manual.)  

                                                73,  Bill  W4ZV


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