Pete KE9OA wrote:

If you ordered Schottky diodes, you ordered the wrong type. You need
PIN
diodes. 1N5767s would do the trick.
It is worthwhile to change the audio coupling caps.

Pete
--------------------------------------------
I haven't ordered anyhting yet, due to house and auto
insurance falling due, I have limited non essenital
spending until June. And the first thing I plan to buy
is a 455.1 500Hz CW filter....

I have read and re-read the Kiwa article many times in in the
last few months. I had read about the Si to IN diode swap for
the 8ve filters several years ago and had the good luck to be
given 24 HP PIN diodes by a grad student. I had forgoten that
I had even made the mod unitl after I purchased another R2000
from Frank C. And I was puzzled by the greater distortion
in the AM band when listening to stations withen a few KHz of a
power house. I initially worte it off as a result of Frank's removal
of the LF/MW 1-dB attenuator. It wasn't until I opened my R2000
for a more complete logic IC bypass mod that I saw the HP PINs
and remembered that I had changed to them.

A mind is a terrible thing to misplace

Any Idea why Kiwa spec'ed PINs for one switch and Shottkys for the
other?

And any links to improved "low distortion" diode detectors,

And any links to any "simple" synch detectors?

Feel free to email me at
r2000swler
at
hotmail
dot
com

Sorry for so many questions bunched in one post.

Terry

"Pete KE9OA" wrote in message
...
1N5767S are good because of their minority carrier lifetime, although any
diode that has at least a 1.5uSec lifetime would be ok.


I've been wanting to do a PIN diode u/g for my DX-394's preselector
bandswitching for a couple of years since reading the Kiwa article. But I
wanted surface mount to directly replace the existing diodes. I think I have
found them for the three SW bands - Infineon BAR64-03W PIN Diodes in a
SOD-323 package with a typical charge carrier lifetime of 1.55us.
http://www.ortodoxism.ro/datasheets/...ar64series.pdf (501 kb)
http://www.ortodoxism.ro/datasheets/...2702-A1045.pdf (48kb)

Pete, do these look like a good alternative to the axial leaded 1N5767?

Still looking for something for the MW and LW bands in a dual diode SOT-343
package to replace the DA277's:
http://www.ortodoxism.ro/datasheets/rohm/da227.pdf (53kB)

73, Tom

If you are just switching bands, why does the carrier lifetime matter?

I've been wanting to do a PIN diode u/g for my DX-394's preselector
bandswitching for a couple of years since reading the Kiwa article. But I
wanted surface mount to directly replace the existing diodes. I think I
have found them for the three SW bands - Infineon BAR64-03W PIN Diodes in
a SOD-323 package with a typical charge carrier lifetime of 1.55us.
http://www.ortodoxism.ro/datasheets/...ar64series.pdf (501 kb)
http://www.ortodoxism.ro/datasheets/...2702-A1045.pdf (48kb)

Pete, do these look like a good alternative to the axial leaded 1N5767?

Those diodes should be fine.

Still looking for something for the MW and LW bands in a dual diode
SOT-343 package to replace the DA277's:
http://www.ortodoxism.ro/datasheets/rohm/da227.pdf (53kB)

73, Tom

Unitrode is another manufacturer to try......................they may have a
suitable replacement.

Pete

It was once explained to me that the longer the minority carrier lifetime,
the better the low frequency response.
These folks explain it much better than I can:
www.microsemi.com/micnotes/701.pdf

wrote in message
oups.com...
If you are just switching bands, why does the carrier lifetime matter?

Pete KE9OA wrote:
It was once explained to me that the longer the minority carrier
lifetime,
the better the low frequency response.
These folks explain it much better than I can:
www.microsemi.com/micnotes/701.pdf

wrote in message
oups.com...
If you are just switching bands, why does the carrier lifetime
matter?


A practical article about this is:
Tom Thompson W0IVJ, Exploring Intermodulation Distortion in RF
Switching and
Tuning Diodes, QST December 1994, pp 25-27

His tests demonstrate that PIN diodes intended for RF switching are
superior to PN switching diodes, especially at low bias. Surprisingly,
the common 1N4007 1A rectifier which has a PIN structure equals or
outperforms the MPN3700 and BAR17 RF PIN diodes for intermod at 5-10mA
bias but its reverse bias isolation would require two of them in series
to match these others.

The 1N4153 PN diode he tested had excellent isolation but lousy
intermod, great for turning something off but poor when turned on!
The author measured a 10-12 dB improvement just by raising the
forward bias from 5mA to 10 mA.

What was especially revealing in this article was the testing of a
varactor diode as the capacitor in a tuned preselector circuit
contrasted to a fixed capacitor switched by a PIN diode. The author
concluded that "using tuning diodes to tune high impedance circuits
in the presence of strong signals is not a good idea". I'll have to
go back to the library because a footnote to this sentence was that
the same issue of QST had an article by Ulrich Rohde, the highly
respected communications engineer, on a diode-tuned filter designed
to minimise IMD.

Tom

Tom wrote:

snip

His tests demonstrate that PIN diodes intended for RF switching are
superior to PN switching diodes, especially at low bias.
Surprisingly,
the common 1N4007 1A rectifier which has a PIN structure equals or
outperforms the MPN3700 and BAR17 RF PIN diodes for intermod at
5-10mA
bias but its reverse bias isolation would require two of them in
series
to match these others.

snip

Tom

Man I wish the R2000 RF deck was easier to get to, I have a boatload,
OK at least 100 1N4007. When a development lab moved from from
Lexington I "inheireted" the parts stashes of several friends who
moved out of the area. This is so tempting it is frightening......

Thanks for something to think about.

Terry

When I read lifetime, in my mind I was thinking shorter was better. In
fact, there are gold doped transistors where the gold is used to lower
the lifetime. However, the paper explained the longer lifetime means
lower resistance Thanks for the reference.

Anytime! It appears that the shorter lifetime diodes are used for the higher
frequencies (VHF / UHF). When I built my first receiver and was looking for
the right type of diode for the preselector, the engineer I was working with
said "you need to use some real slow dogs for these frequencies".
In one of Rohde's notes, I remember his stating that a diode with a 1.5uSec
minority carrier lifetime is usable down to around 200kHz. I have had good
experience with 1N5767s down to 10kHz, but I am sure that there is a rolloff
in sensitivity.

Pete

wrote in message
oups.com...
When I read lifetime, in my mind I was thinking shorter was better. In
fact, there are gold doped transistors where the gold is used to lower
the lifetime. However, the paper explained the longer lifetime means
lower resistance Thanks for the reference.

Would the 1N5767S be a good replacement for the front-end bandpass
filter switching diodes in an R8? Drake used a 1SS135.

Pete KE9OA wrote:

Anytime! It appears that the shorter lifetime diodes are used for the higher
frequencies (VHF / UHF). When I built my first receiver and was looking for
the right type of diode for the preselector, the engineer I was working with
said "you need to use some real slow dogs for these frequencies".
In one of Rohde's notes, I remember his stating that a diode with a 1.5uSec
minority carrier lifetime is usable down to around 200kHz. I have had good
experience with 1N5767s down to 10kHz, but I am sure that there is a rolloff
in sensitivity.

Pete

wrote in message
oups.com...
When I read lifetime, in my mind I was thinking shorter was better. In
fact, there are gold doped transistors where the gold is used to lower
the lifetime. However, the paper explained the longer lifetime means
lower resistance Thanks for the reference.


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