[Yaesu] 1000MP - Decreased Signal Strength on Low Bands
Tyler Stewart
Tyler Stewart" <k3mm@erols.com
Mon, 1 Jan 2001 22:50:07 -0000
Well, hang on a minute.
You SHOULD see a decrease in sensitivity on frequencies below 7 mhz in TUNED
mode. TUNED mode on the low frequencies kicks in a higher dynamic
range/lower sensitivity preamp. Usually this is good choice, but not for
low sensitivity RX antennas such as bevs, EWE's, etc., unless you run a lot
of preamplification before it hits the radio RX ANT IN jack.
If you still think there is a problem on 80, try passing through the BPF
crossover points at 3 and 4 mhz and see if the sensitivity changes as you
pass through 80. If it drops at all, you've probably got damage in your RX
BPF for 3 to 4 mhz (I've had a coil short out there as well).
The key thing to remember on any radio is that you should be hearing
atmospheric static in the background over the normal hiss of the RX with no
antenna. If you dont, you arent going to hear the weakest signals. Do
whatever you need to do to fix the problem.
The flip side is that you shouldnt run more gain than you need, especially
on crowded bands as this just invites RX overload. I've found that using
the RF Gain control on the MP seems to be the best choice over other options
such as the attenuator and the IPO button.
73, Ty K3MM
----- Original Message -----
From: "Ken Claerbout" <K4ZW@Staffnet.com>
To: "Tyler Stewart" <k3mm@erols.com>; <yaesu@contesting.com>
Sent: Monday, January 01, 2001 9:53 PM
Subject: Re: [Yaesu] 1000MP - Decreased Signal Strength on Low Bands
>
> Thanks for the suggestions Ty. Using my 80 meter 4 square, I have a
local
> line noise of S6 when in the tuned position and S9 in the flat setting.
> Switching the 4 square between the Antenna A jack and RX Ant In, I did not
> see any change. The same thing happens on 40 & 160 although it seems to
be
> most pronounced on the low end of 80 meters. Any other suggestions?
>
> 73
> Ken K4ZW
>
> ----- Original Message -----
> From: "Tyler Stewart" <k3mm@erols.com>
> To: "Ken Claerbout" <K4ZW@Staffnet.com>; <yaesu@contesting.com>
> Sent: Monday, January 01, 2001 6:31 PM
> Subject: Re: [Yaesu] 1000MP - Decreased Signal Strength on Low Bands
>
>
> > Try using the RX In jack and see if everything sounds normal. If so, it
> > sounds like a bad high pass filter section. The RX ANT In jack bypasses
> > this board. This is on a separate board before the main RX RF board and
I
> > believe is only IN when in TUNED mode and is not in line when using a RX
> > antenna. If it still occurs, I almost guarantee, it's the 80 meter BPF
> > section in the receiver. Note that the BPF's are always in no matter
what
> > preamp you are using.
> >
> > I've had problems with this and some of the bandpass filter sections in
> the
> > receiver. What I've found every time is that the little molded coils
they
> > are using short out some turns. It's not something you can find
visually.
> > You have to start lifting leads and measuring or just shotgun
> replacement.
> >
> > I just dug out my tech manual for the MP and have noted that L3503 on
the
> > HPF-UNIT is the first coil to ground in the 80 M HPF and has failed once
> on
> > both of my MPs! It's a 1.8uH rf choke and it's Yaesu part # L1790049.
> >
> > Note that this is a very easy board to work on. It's located near the
> right
> > rear top of the radio behind the AFC board and just in front of the A/B
> > relay board in front of the SO239 jacks. It's mounted on a couple of
> > plastic, snap-in standoffs and the board should be marked with the L3503
> > designator.
> >
> > SHould be an easy fix if you can handle basic electronic repair!
> >
> > 73, Ty K3MM
> >
> >
> >
> > ----- Original Message -----
> > From: "Ken Claerbout" <K4ZW@Staffnet.com>
> > To: <yaesu@contesting.com>
> > Sent: Monday, January 01, 2001 2:28 AM
> > Subject: [Yaesu] 1000MP - Decreased Signal Strength on Low Bands
> >
> >
> > >
> > > I noticed during the CQWW CW contest this past November, that signals
on
> > 80
> > > meters seemed unusually weak. With all the solar activity going on
that
> > > weekend, I wrote it off to poor conditions. Thinking about this a bit
> > > further, I recall that over the past month or two, 80 meters has
sounded
> > > unusually quiet. I decided to do a side by side comparison with my
> > Kenwood
> > > 940 and promptly noticed that signals on 80, including power line
noise,
> > > were 20 dB weaker on my 1000MP. No wonder I was having a hard time
> > chasing
> > > the weak DX stations! Taking a closer look, I also see this happening
> on
> > 40
> > > & 160 although it was not apparent until now.
> > > I swapped the two rigs just to eliminate any potential problems
with
> > > cables, filters, or something specific to that operating position and
> the
> > > problem followed the radio (1000MP).
> > > The radio is set for a tuned front end and when I switched it to
> flat,
> > > using the broad front end amp, signals came back up on all three
bands.
> > > This would seem to indicate that there is a problem with the low band
> > tuned
> > > RF amp. However, the diagram in the manual labels the range for this
> amp
> > as
> > > 1.9 - 7 Mhz. Is this front end section actually in use on 160 meters
in
> > the
> > > 1.8 - 1.9 Mhz range and also on 40 meters between 7 Mhz and 7.3 Mhz
or
> is
> > > the wide band amp used in these frequency ranges? If it's the latter,
> > then
> > > that kind of kills my theory about the low band amp. Is there
anything
> > else
> > > setting wise etc. that I should be checking?
> > > In the event I have to get this repaired, I'd appreciate
suggestions
> > as
> > > to where I should have this done.
> > >
> > > 73
> > > Ken - K4ZW
> > >
> > >
> > >
> > >
> > > --
> > > FAQ on WWW: http://www.contesting.com/FAQ/yaesu
> > > Submissions: yaesu@contesting.com
> > > Administrative requests: yaesu-REQUEST@contesting.com
> > > Problems: owner-yaesu@contesting.com
> > >
> > >
> >
> >
>
>
> --
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>
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