On Oct 7, 11:58*am, Bob wrote:
Hi,

A bit off topic, but I figure you folks are the true theorists out
there, and would probably know about this.

Am thinking about purchasing a shortwave defined radio receiver from
WinRadio (http://www.winradio.com/home/g33ddc.htm).

Here is copy from part of their spec sheet:

* * *"The receiver's robust front-end is equipped with an
ultra-high-linearity amplifier which results in exceptional
strong-signal performance. This already robust front-end is further
enhanced with a user-selectable preselector that can operate either in a
fully automatic or user-configurable mode. As many as 119 different
filter combinations can be constructed by the user (91 bandpass, 14
low-pass and 14 high-pass). The front-end employs 34 subminiature
electromechanical relays (rather than often used but distortion-prone
semiconductor switches) to ensure high dynamic range."

Was really surprised to see: The front-end employs 34 subminiature
electromechanical relays (rather than often used but distortion-prone
semiconductor switches) to ensure high dynamic range.

I am retired now, so haven't kept up withese things, or the state of the
art nowadays, but are they still using electromechanical relays for
front ends feeding a 16 bit A to D ?

Haven't semiconductor switches, caught up with reed relays for this
application by now, or do they "still" provide a lower "on" resistance,
etc. ?

Any thoughts would be most appreciated.

Thanks,
Bob
Excuse me, Bob, but no where in the description do they mention reed
relays. I really doubt they are using reed relays because of the open
capacitance of the contacts, plus, reed relays often stick shut
because of fatigue, static electricity, and if left closed for a long
time, metal migration will stick them closed.

Bet they are using regular relays, but in miniature form.

Paul

On Thu, 7 Oct 2010 13:49:12 -0700 (PDT), "
wrote:

I really doubt they are using reed relays because of the open
capacitance of the contacts,

Measuring in at 0.1pF? the 1N914 (UHF switching diode) is easily 10
times this and more.

plus, reed relays often stick shut

Ma Bell used them in the millions with 99.999% up-time.

because of fatigue,

We are talking about a switch rated in the 100 Millions to Billions of
operations.

static electricity, and if left closed for a long
time, metal migration will stick them closed.

That is true with issues compounding this, but as the receiver has its
own spectral display, problems will be shown to you directly.

Bet they are using regular relays, but in miniature form.

Which would suffer the same issues you offer above.

Reed relay usage design is not for the faint of heart, but when
properly matched (an ugly word here) to the load, then they can
provide service beyond your (and your children's) lifetime in this
application.

73's
Richard Clark, KB7QHC