"Jan-Martin Noeding, LA8AK" wrote in message
...
On Mon, 23 Feb 2004 21:33:39 -0500, "Tom Holden"
wrote:


I seized on the word "delayed" and linked it to the inclusion of a longer
time constant in the AGC to the RF stages of the DX-394 than the time
constant in the AGC to the IF stages. The Handbook example actually says
"As
an option, the AGC to the RF amplifier is held off, or 'delayed', by the
0.6V forward drop of the diode so that the RF gain does not start to
decrease until larger signals appear. This prevents a premature increase
in
the receiver noise figure. Also, a time constant of one or two seconds
after
this diode helps keep the RF gain steady for the short term."

Mentioning a certain voltage level doesn't really make so much sense
when you don't know what the rest of detector stages looks like.
73, LA8AK


Jan-Martin,

I think the issue is that it is NOT a time delay, but a signal level
delay. The AGC does not begin to reduce receiver gain until the signal
reaches some defined LEVEL.

--
Steve N, K,9;d, c. i My email has no u's.

"Tom Holden" wrote in message
.. .
Jan-Martin Noeding, LA8AK wrote:
Mentioning a certain voltage level doesn't really make so
much sense when you don't know what the rest of detector
stages looks like. [snip]

Thanks for the interesting examples, Jan-Martin. The quote was from the
2004
ARRL HB page 17.23 in reference to a schematic/block diagram of a "typical
superhet receiver with AGC applied to multiple stages of RF and IF". The
RS
DX-394 bears some resemblance to this with a resistor in place of the
"Delay
Diode". It beats me how the AGC in this HB example actually controls the
RF
gain - the diode appears to block control. A second one in parallel in the
opposite direction seems to me to be needed.

Tom


Tom,

I don't have the circuit, but have two diodes pointing down. Resistors
on both anodes to +V. Common cathodes with resistor to GND.

+V
___|______
| |
R1 R2
a_| |_b
| |
V V
- D1 - D2
| |
| |
__________
|
R3
|
|
GND

Changing the voltage at point "b" will cause "a" to also change. Another
way to look at it is that you steal different amounts of current away from
D1. Go too low at "b" and "a" won't change any more. It stops. However,
go higher on "b" and "a" keeps going up. It is a limiter.

--
Steve N, K,9;d, c. i My email has no u's.

"Tom Holden" wrote in message
.. .
Jan-Martin Noeding, LA8AK wrote:
Mentioning a certain voltage level doesn't really make so
much sense when you don't know what the rest of detector
stages looks like. [snip]

Thanks for the interesting examples, Jan-Martin. The quote was from the
2004
ARRL HB page 17.23 in reference to a schematic/block diagram of a "typical
superhet receiver with AGC applied to multiple stages of RF and IF". The
RS
DX-394 bears some resemblance to this with a resistor in place of the
"Delay
Diode". It beats me how the AGC in this HB example actually controls the
RF
gain - the diode appears to block control. A second one in parallel in the
opposite direction seems to me to be needed.

Tom


Tom,

I don't have the circuit, but have two diodes pointing down. Resistors
on both anodes to +V. Common cathodes with resistor to GND.

+V
___|______
| |
R1 R2
a_| |_b
| |
V V
- D1 - D2
| |
| |
__________
|
R3
|
|
GND

Changing the voltage at point "b" will cause "a" to also change. Another
way to look at it is that you steal different amounts of current away from
D1. Go too low at "b" and "a" won't change any more. It stops. However,
go higher on "b" and "a" keeps going up. It is a limiter.

--
Steve N, K,9;d, c. i My email has no u's.

Avery Fineman wrote:
[snip]
As to the attack and decay times you specified, seems
good to me. That can be set to suit the individual
listener.

Len Anderson
retired (from regular hours) electronic engineer person

Here is my survey on which I based my targets:

Release-ms
Receiver Attack-ms Slow Medium Fast

AOR AR7030 2/8 SSB/AM 1800 400 -
Collins 75S-3B/3C 1 600 190 -
Drake R4C 1 1000 350 50
Drake R8B 1 2000 300 -
Grundig Satellit 800 1 3000 300 -
Rockwell/Collins HF-2050
30 3500-10000 250+/-50 -


U.S. Federal 30 800-1200
SSB/ICW modes
Telecommunication
Recommendation 1050-1998
"HF Radio Automation
Link" 13
25 Data Mode

Design Target 1-13 1800-3000 300 25

I wonder if there is any merit in making the attack selectable within a
range of 1-30 ms.

Tom

Avery Fineman wrote:
[snip]
As to the attack and decay times you specified, seems
good to me. That can be set to suit the individual
listener.

Len Anderson
retired (from regular hours) electronic engineer person

Here is my survey on which I based my targets:

Release-ms
Receiver Attack-ms Slow Medium Fast

AOR AR7030 2/8 SSB/AM 1800 400 -
Collins 75S-3B/3C 1 600 190 -
Drake R4C 1 1000 350 50
Drake R8B 1 2000 300 -
Grundig Satellit 800 1 3000 300 -
Rockwell/Collins HF-2050
30 3500-10000 250+/-50 -


U.S. Federal 30 800-1200
SSB/ICW modes
Telecommunication
Recommendation 1050-1998
"HF Radio Automation
Link" 13
25 Data Mode

Design Target 1-13 1800-3000 300 25

I wonder if there is any merit in making the attack selectable within a
range of 1-30 ms.

Tom

"Tom Holden" ) writes:
Avery Fineman wrote:
[snip]
As to the attack and decay times you specified, seems
good to me. That can be set to suit the individual
listener.

Len Anderson
retired (from regular hours) electronic engineer person

Here is my survey on which I based my targets:

Release-ms
Receiver Attack-ms Slow Medium Fast

AOR AR7030 2/8 SSB/AM 1800 400 -
Collins 75S-3B/3C 1 600 190 -
Drake R4C 1 1000 350 50
Drake R8B 1 2000 300 -
Grundig Satellit 800 1 3000 300 -
Rockwell/Collins HF-2050
30 3500-10000 250+/-50 -


U.S. Federal 30 800-1200
SSB/ICW modes
Telecommunication
Recommendation 1050-1998
"HF Radio Automation
Link" 13
25 Data Mode

Design Target 1-13 1800-3000 300 25

I wonder if there is any merit in making the attack selectable within a
range of 1-30 ms.

Tom


Traditionally, the circuitry was too bulky to make it more complicated,
so there was always tradeoff. With semiconductors the added circuitry to
make attack and decay independent doesn't require much space, or added
cost. Once one has that in place, one can fiddle with the actual times.
Maybe making it completely variable is not useful, but it'll only cost
a switch to add multiple times.

Michael VE2BVW

"Tom Holden" ) writes:
Avery Fineman wrote:
[snip]
As to the attack and decay times you specified, seems
good to me. That can be set to suit the individual
listener.

Len Anderson
retired (from regular hours) electronic engineer person

Here is my survey on which I based my targets:

Release-ms
Receiver Attack-ms Slow Medium Fast

AOR AR7030 2/8 SSB/AM 1800 400 -
Collins 75S-3B/3C 1 600 190 -
Drake R4C 1 1000 350 50
Drake R8B 1 2000 300 -
Grundig Satellit 800 1 3000 300 -
Rockwell/Collins HF-2050
30 3500-10000 250+/-50 -


U.S. Federal 30 800-1200
SSB/ICW modes
Telecommunication
Recommendation 1050-1998
"HF Radio Automation
Link" 13
25 Data Mode

Design Target 1-13 1800-3000 300 25

I wonder if there is any merit in making the attack selectable within a
range of 1-30 ms.

Tom


Traditionally, the circuitry was too bulky to make it more complicated,
so there was always tradeoff. With semiconductors the added circuitry to
make attack and decay independent doesn't require much space, or added
cost. Once one has that in place, one can fiddle with the actual times.
Maybe making it completely variable is not useful, but it'll only cost
a switch to add multiple times.

Michael VE2BVW

Steve Nosko wrote:
Thanks for the interesting examples, Jan-Martin. The
quote was from the 2004 ARRL HB page 17.23 in reference
to a schematic/block diagram of a "typical superhet
receiver with AGC applied to multiple stages of RF and
IF". The RS DX-394 bears some resemblance to this with a
resistor in place of the "Delay Diode". It beats me how
the AGC in this HB example actually controls the RF gain
- the diode appears to block control. A second one in
parallel in the opposite direction seems to me to be
needed.
I don't have the circuit, but have two diodes
pointing down. [snip]
That's interesting, Steve but the circuit looks like this:

RF Amp----MXR------IF Amp
| |
R R
|------|---------|
| | D |
C R ---from AGC
| |
-----
|
GND

Just noticed an asterix by the 'delay' Diode that says it may be replaced by
a test-selected resistor - that's the way the DX-394 is done.

Tom

Steve Nosko wrote:
Thanks for the interesting examples, Jan-Martin. The
quote was from the 2004 ARRL HB page 17.23 in reference
to a schematic/block diagram of a "typical superhet
receiver with AGC applied to multiple stages of RF and
IF". The RS DX-394 bears some resemblance to this with a
resistor in place of the "Delay Diode". It beats me how
the AGC in this HB example actually controls the RF gain
- the diode appears to block control. A second one in
parallel in the opposite direction seems to me to be
needed.
I don't have the circuit, but have two diodes
pointing down. [snip]
That's interesting, Steve but the circuit looks like this:

RF Amp----MXR------IF Amp
| |
R R
|------|---------|
| | D |
C R ---from AGC
| |
-----
|
GND

Just noticed an asterix by the 'delay' Diode that says it may be replaced by
a test-selected resistor - that's the way the DX-394 is done.

Tom