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Old February 4th 05, 03:38 AM
Pete KE9OA
 
Posts: n/a
Default HF150 measurements

I just got through characterizing this unit. MDS = .15uV across the entire
tuning range. Not bad. Overload point = 120mV.
Icom R75..............................................M DS = .07 to .1uV
across tuning range. Overload point = 110mV
Palstar R30 MDS = .06 to .1uV
across tuning range Overload point = 500mV
KE9OA MW receiver (to be marketed someday MDS = .1uV
Overload point = 100mV

I am beginning to think that many of the radio manufacturers are measuring
their overload points using the hard measuring technique, whereby instead of
hooking up the RF Generator directly to the antenna input of the Rx, they
are first running the generator through a 50 Ohm through load ( I do have
some of these types of loads).

I my area of Northern Illinois, the HF150 did a good showing for itself, but
the LW band did have some IM products from the local MW broadcasters. My AOR
7030, which also has a wide open front end, did not exhibit this sympton.
This is the first time I actually had one of these Lowe units open. If they
weren't going for those silly eBay prices, I would probably pick one up as
an extra toy to have around. It seems that the last three units that my
friends picked up had that blown first mixer problem. Now, this could be
solved if an RF limiter diode were placed ahead of that SL6440. It looks
like the input transformer does not have its primary returned to DC ground,
instead, providing V+ for the preamp transistor.
Oh well.................some of these design problems show up when it is too
late. Looking at the schematic, there are back to back diodes ahead of that
preamp transistor. Now, why would they go through all of the trouble to
protect that 25 cent transistor and not protect the expensive mixer? Beats
me!!!!!!!!!

Pete