I remember that for several RadCom issues (Technical Topics)
some articles were published on this matter, and some
measurements made in DL confirmed the good behaviour
of the BA379 for HF Rx front end switching.
The Temic's (former Telefunken) BA479 (G or S suffix) are
specified for 10 MHz to 1 GHz freq range. The specified
minority carrier lifetime is unusually high (4 us) when compared
with some other pin used in HF transceivers and it shall be
good for HF (as I remember, the 1SV128 used for the TS870
Rx input switching is specified for only 250 ns, but still better
than the "standard" 100 ns for many of the VHF parts).
A larger minority carrier lifetime is better for MF/HF and for
attenuators also, and the HP's 5082-3081 is also of this kind.
The usually drawback for this is the slightly higher equivalent
forward resistance (higher losses) for the same bias.
The BA379 and 479 were used for TV input stages also and
were really inexpensive when compared with other pin diodes.
The HP's -3081 are very expensive.
Other good candidates for MF/HF applications are the Infineon's
(former Siemens) BA595, BA885 , BA895 which are specified
for 1 MHz to 2 GHz, 1.6 us, a typical equivalent resistance of
4.5 ohm at 10 mA and they are SMD, so they may be better
for replacing the existing front end switching diodes of the
modern MF/HF transceiver than the -3081.
It may not be the case, but you may have to check also for the
existing diode bias, if it is to low, you may obtain a better IMD
response mostly because of the attenuation introduced by the
replacements, hi, hi.
The BA479 may have an equivalent r of about 15 ohm at 2 mA bias,
and when considering four series diodes (2 for each of the bandpass
filters and 2 for the preamp), you may obtain a good IMD response
solely because of the suplemental 6dB of attenuation introduced by
the low biased pin substitutes.
They have to be biased for about 10 mA, and maybe much more
for the -3081 for lower losses. As I remember, one of the RadCom
articles feedback pointed to this possibility.
73,
Greetings from Bucharest,
Traian, YO9FZS
Jan Erik Holm wrote:
> There are other diodes that can be used in that
> application.
> You might try BA379 (or BA479), low cost compared
> to the HP diode.
>
> 73 good luck / Jim SM2EKM
> -------------------------------------------------------
> Alek Petkovic wrote:
> > Anybody know of a cheap source of 5082-3081 Pin Diodes?
> >
> > We are looking to buy 100 or so to modify some FT-1000MP transceivers.
> >
> > They are extremely expensive here downunder.
> >
> > 73, Alek
> > VK6APK
> >
> > http://www.qrz.com/vk6apk
> > http://profiles.yahoo.com/vk6apk
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> >
>
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