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

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

Pete KE9OA wrote:
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


Pete,

A while back you were sending out mods to improve the AR3030. If you
still have them or any more that you discovered I would really
appreciate it if you could pass them along to me.

Pete KE9OA wrote:
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.

Kenwood units often have extra anttenuation below the 160 meter ham
band to prevent strong broadcast stations from overloading the front ends.

On units sold in the U.S., they often increased it without documenting it.
As an example, my TS-430 had a 220 ohm resistor instead of the (what I
remember as) an 80 ohm one. I replaced it with a 22 ohm resistor from a
"mod" I found and it helped.

My R-5000 also benefitted from a similar "fix".

When I did live in the U.S. (Philly) I was less than five miles from several
AM broadcast transmitters and needed it. Here in Jerusalem, it's the other
way around. Without the mod, the best I could ever get from an AM
broadcast station was S9.

Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

wrote in
oups.com:

Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Frank


If you can stick with PIN diodes.

They give better isolation when reverse biased that other types.