Oftentimes, it is the type of ferrite material used in the mixer baluns.
Also, it could be that low Q caps are being used in the lower bands. I have
both an NRD-515 and an NRD-91. Both of these receivers exhibit rolloff below
700kHz.
These comparisions are made, using a Drake R7, Palstar R30, Yaesu FRG-100,
Icom R-75, Lowe HF150, HF-225, and HF-250. I did repair a Kenwood R-2000 a
few years ago, and wondered if it had some sort of attenuation below 1.5MHz.
I noticed this same characteristic with a Kenwood R-5000 and an AOR-3030.

Pete

wrote in message
ps.com...

wrote:
There's no question that the 1N400X series is a poor switching diode
when it comes to speed and reverse recovery characteristics, however,
for switching in and out bandpass filters I think the reverse bias
junction capacitance is the major issue to prevent unwanted signal
coupling. I would definitely look for true PIN diodes if I were
upgrading the filter switching diodes rather than use 1N4007s. It's
just interesting that there have been articles on the fact that they
appear to work reasonably well in some cases. I know the Kenwood
R-2000 I had used the equivalent of 1N914s for these diodes in the
front end and they were horrible with all kinds of cross talk from
stronger, out of band signals.

Frank

---------------
The R2000 uses BA282 band filter switch diodes.

The RX Unit (X55-1340-00) in the R2000 sevice manual gives the
part number, which I just verified by looking at the stock diodes
that I saved when I upgraded both of my R2000s.

See http://www.vishay.com/diodes/list/product-85526/

For the 6MHz and 9MHz bands, good HP PINs give a slight but
noticable improvement. I expected a big improvement in the below
500KHz range but found nothing that I could hear.

I still lurk and will make the odd post when I have something usefull
to add. All prior Email accounts are abandoned and dead.

Terry