Re: New Mixer

---------

From: Paul Harden (pharden@aoc.nrao.edu)
Date: Fri Mar 24 1995 - 17:41:08 EST


>From: Clark Fishman (FSAC) <cfishman@fsac3.pica.army.mil>
>Subject: New Mixer
>
>I just got a data sheet from Analog Devices on the AD831 Low Distortion
>Mixer....this puppy is a modified Gilbert cell mixer with built in
>amplifiers on all ports...you gets +24 DBM 3rd order intercept with only
>-10 DBM local oscillator drive...... The amplifiers are direct coupled
 (snip)
>without all those Toko coils....Bad news (sorta) These mixer draw
>about 100 ma from the power...I can live with that...now to get
>some samples......
>
>WA2UNN Clark Fishman cfishman@pica.army.mil

I have just received some samples and a development board from Analog
Devices for a product they hope to start fabricating this summer. It is
the AD607 and AD608. It is a super beefed up NE602 in the front end,
followed by 100dB of IF amps, with breakouts for adding external ceramic
or crystal filters (IF drives a 300 ohm load!), with both an in-phase and
quadrature detector driven from on on-board PLL, etc. You can either use
the internal 80-dB range AGC, derived from full-wave detectors off each
IF amp, or apply your own external AGC. If using the internal AGC, the
AGC "pin" becomes an RSSI/S-meter drive. It draws 7.8mA with full IF gain.
It also has a control pin to put the chip into a 300uA standby mode, which
switches OFF in 1uS and ON in 500nS --- thus I'm hoping I can utilize this
feature as a direct T-R switch for the receiver.

I've started breadboarding/modifying the development board for a 40M
QRP rig. (The development board is intended for a 450MHz receiver!) Not
very far along yet (got carried away designing a VFO for it to select
either LSB or USB ... something I always wanted to do on a QRP rig). But
gonna build a prototype using both chips to see which one works the best.
At this time, it appears one would be suitable for a very low parts count
QRP rig, while the other could be the answer to a very stable QRP receiver
approaching the performance of commercial rigs (with a proportional number
of additional components!). Expected introduction cost of the chip is
$15-20 (the marketing dept. really had no idea) with hopes it will be a
$5-8 chip once into their third or fourth production run. She claimed they
had orders already to backlog them 6 months once they start fabrication.
Obviously they've had ONE small production run, or else I wouldn't have a
couple of them and a development board in front of me.

Anyway, I can keep the list informed of the development and progress if
there is any interest. And perhaps while on the subject, anybody got any
neat ideas on what they would like to see in a new generation QRP rig?
There's some amazing gagetry out there for $1 or 2. Some of 'em sitting
here on my work bench. (Some of those salesmen can sure be generous!).
I'm also playing around with a new directional coupler hybrid IC (about $2)
that can be used to isolate XMT power from the RCVR with its 90dB of
isolation ... i.e., automatic full-QSK with "no moving parts." (This is fun,
considering my job is to build DIGITAL circuits).

Have a good weekend on HF ...
Paul NA5N

----NATIONAL RADIO ASTRONOMY OBSERVATORY ----- Socorro, New Mexico -----
| VLA - Very Large Array Observatory - Worlds largest radio telescope |
|VLBA - Very Long Baseline Array - even larger |
--------(pharden@zia.aoc.nrao.edu) --- (73 de NA5N) --------------------


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