In a Mastr II if everything is correct, you should perceive no
difference from [EMAIL PROTECTED] to [EMAIL PROTECTED] I suspect the IF
alignment
is off. You do not need a sinnader to check this. Most Mastr II are
11.2 mhz IF , some are 9.4.... Close couple a strong 5kz deviation
1khz tone at 11.2 Mhz in the IF housing and watch the audio with a
scope at vol hi.. If it is flat topping on one side or the other, it
is misalligned, if the sine wave is slanted it is misalligned...
Decrease the rf signal and see if it stays clean down into the
noise... Obvious distortion will be visible if it is mis tuned..
Assuming the IF is correctly aligned the next likely culprit is the
rx is off freq....The CORRECT procedure is to set the absolute rx
freq is to measure the IF injection freq by sticking a probe into the
mixer area and reading the LO which should be Operating freq -11.2
mhz ( or 9.4 ).....When this is set this way, assuming you can
generate the proper input on the operating freq, the absolute
difference is the IF freq which should be processed into symmetrical
audio at vol hi.....
An absolute test to see if the IF is aligned properly is to set the
freq this way, then inject the operating frq into the rx and monitor
the vol hi with a scope, if ANY flat topping or unsymetrical image is
viewed, the IF is misaligned.... or maybe bad IF xtals....
The problem is over time folks mess with the IF and get it
mis-centered and the only way to correct for this is to change the
injection freq to compensate..this works to a point until you run
into the rails of the IF crystal filters which do not move....The
proper procedure is to align the rx around a know proper injection
freq. This is actually the only finite measurable part as the rest is
all interpretation by ear or by sinnader...( or a scope ).
The Mastr II rx under normal properly tune circumstances should be
flattening off symmetrically at just above 5khz deviation....by 7 is
should be all but square waves... They key is this should be visibly
symmetrical as you increase the signal while viewing vol hi on a scope....
Vol HI actually does exhibit some distortion normally as it is after
some filtering.. Any sloping of the sine wave indicates alignment
issues in the IF...
Doug
KD8B
At 12:44 PM 3/4/2006, you wrote:
>I've noticed that I can get a lot better sensitivity on my receivers if
>the source I'm measuring against is either unmodulated, or I set the
>deviation to 1 or 2 kHz. When I get up to 3-5 kHz deviation, the
>apparent sensitivity of the receiver is significantly less.
>
>I notice this on many systems, where a weak station will be "in" until
>they talk a little louder, then they drop out.
>
>Is there a tuning method I can use to minimize this effect?
>
>
>
>
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
