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

In article ,
"Pete KE9OA" wrote:

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).

Snip

Most RF generators are calibrated to a 50 ohm load. This load must be
resistive in order to actually "burn power" against the generators
output source impedance. Not having this resistive load means the
generator output will be higher than calibrated. The generator is
probably designed to be 50 ohms so if you connected it to a 100 ohm
resistor you would have something like two times the indicated swing of
the generator. The front end of most radios are reactive and their
resistive component is large so I expect that the best thing to do is
use a 50 ohm resistor across the receivers input terminals.

--
Telamon
Ventura, California

That makes sense................I will try those measurements with the
series load. This explains quite a bit............thanks.

Pete

"Telamon" wrote in message
...
In article ,
"Pete KE9OA" wrote:

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).

Snip

Most RF generators are calibrated to a 50 ohm load. This load must be
resistive in order to actually "burn power" against the generators
output source impedance. Not having this resistive load means the
generator output will be higher than calibrated. The generator is
probably designed to be 50 ohms so if you connected it to a 100 ohm
resistor you would have something like two times the indicated swing of
the generator. The front end of most radios are reactive and their
resistive component is large so I expect that the best thing to do is
use a 50 ohm resistor across the receivers input terminals.

--
Telamon
Ventura, California