K2: AGC versus RF Gain versus AF gain

[Michael J. Linden]

  I've only seriously used two other HF rigs besides the K2, that is a
Kenwood TS-530S and a Kenwood TS-930S. So, when I make comparisons, its
between the K2 and the Kenwoods. When I have the AGC set to FAST on the
Kenwoods and am receiving a CW signal at say S-9, I can turn the RF gain
down to say S-5 (to reduce background noise) and not notice a
significant reduction in the volume of the received signal. However,
when I do the same thing on the K2, I do notice a reduction in the
volume level. Is this normal for the K2?
 
  I have the AGC set at 3.8V on the K2 and I notice only a little
difference between the background noise of a quiet band when I switch
the AGC on and off. Perhaps I still need to fine-tune the AGC a bit
downwards on the K2 or it may just be that the K2's RF gain and AGC
circuitry takes a different approach than Kenwood used to.
 
  Thanks, Michael N9BDF, K2 #4137
 
 
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[G3VVT]

Micheal,
 
The so called RF gain in the K2 is actually IF gain, which is the same as  
used in the JRC NRD-515 RX. The difference is the K2 has fixed RF front end  
gain before the RX mixer with a switchable preamp or attenuator in addition. The  
NRD-515 has no RF amplifier only a switchable RF attenuator in front of the
1st  RX mixer. Not familiar with what the Kenwood RF gain does in the TS-530S
or the  TS-930S.
 
The K2 has a slightly strange action in that a strong signal goes to a  
higher S meter reading pretty much as soon as the RF gain is reduced and when  the
S meter reading goes higher the RX volume does go down as you say. Not a lot  
but perceptible. It is possible to set the S meter with no signal in to the  
level required, say S9, though when a station is tuned in that was S9 with full
 RF gain it now reads higher and the audio volume is less.
 
The JRC NRD-515 volume stays constant until a point is reached that the S  
meter reading rises with reduced RF gain and becomes greater than the reading  
for the incoming signal. The RX audio volume then begins to fall beyond that  
point
 
Looks like a quirk with the K2 AGC action or design.
 
My K2 has had the AGC threshold set to the point where switching the AGC on  
and off has no effect on the no signal background noise. Came out in my case
at  3.70V, though apparently varies slightly from K2 to K2
 
Bob, G3VVT
K2 #4168
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Don Wilhelm-3]

Michael,

Several factors come into play here:
For best sensitivity, you should adjust your K2 so that you discern no
change in the audio level when changing from AGC on to AGC off on a dead
band (caution - a high local noise level on the 'dead band' may cause an
erroneous conclusion).

The S-Meter reading on the K2 may not correspond to the S-meter reading on
your Kenwoods (I don't know what calibration 'standard' Kenwood uses for
S-meter readings).

The AGC (and S-Meter action) on your K2 can be adjusted with combinations of
AGC Threshold, S-LO, and S-HI settings.  If you have the Elecraft SG-1 (or
other constant level signal generator), you can set S-9 equal to 50 uV with
careful manipulation of the above 3 settings - making a chart of the
combinations and the resulting S-Meter activity will help in deciding which
way to move each of the 3 settings to achieve whatever your goal may be.
Some compromise may be the 'correct' answer.

Because S-Meter readings are not subject to any real standards, directly
comparing the K2 to any other receiver may be an exercise in frustration.
After all, "REAL" S (signal Strength) reports are subjective, and reflect
the perception of the receiving station rather than some absolute standard.

73,
Don W3FPR

----- Original Message -----

>  I've only seriously used two other HF rigs besides the K2, that is a
> Kenwood TS-530S and a Kenwood TS-930S. So, when I make comparisons, its
> between the K2 and the Kenwoods. When I have the AGC set to FAST on the
> Kenwoods and am receiving a CW signal at say S-9, I can turn the RF gain
> down to say S-5 (to reduce background noise) and not notice a
> significant reduction in the volume of the received signal. However,
> when I do the same thing on the K2, I do notice a reduction in the
> volume level. Is this normal for the K2?
>
>  I have the AGC set at 3.8V on the K2 and I notice only a little
> difference between the background noise of a quiet band when I switch
> the AGC on and off. Perhaps I still need to fine-tune the AGC a bit
> downwards on the K2 or it may just be that the K2's RF gain and AGC
> circuitry takes a different approach than Kenwood used to.
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[John Magliacane]

As others have pointed out, only a single I.F. amplifier chip is gain
controlled in the K2.  The RF gain, the gain of post mixer I.F. amplifier
transistor, and the gain of the active product detector are not controlled
through AGC, yet they all contribute to the receiver's total gain.

Since the I.F. amplifier chip has a gain range of about 50 db (min to
max) (if memory serves correctly), that's about all the AGC range you'll
have for the entire receiver as a whole.  The RF attenuator/bypass/RF
amplifier provide about 24 dB (-10 db to +14 db) of manual gain control.
The volume control provides the rest.  :-)

About 20 years ago I converted an old Hammarlund HQ-140-X receiver
to a solid state design.  The Hammarlund's AGC controlled the gain
of the RF amplifier and three I.F. amplifiers (all 6BA6 remote
cutoff pentodes).  I kept the same philosophy after converting
each of these stages to 40673 MOSFETs.

The input of each 455 kHz I.F. stage was (is) through a tap on each
of the I.F. interstage transformers.  This "gain deprives" each I.F.
amplifier a bit, and is possibly done for maintaining stability, rather
than for reasons of impedance matching.  However, since there's still
more gain than is needed for the receiver, and since ALL of the RF
and IF stages are AGCed, a tremendous amount of AGC range is
available.  (Significantly more than if only 2 I.F. stages were
used without the gain-depriving transformer taps.)

The result of having nearly all of the receiver's total gain under AGC
control is that the difference in volume when tuning between a strong
signal (such as an AM broadcast) and an empty band (10-meter band noise
at night) is almost negligible.

With a large amount of receiver gain under AGC control, the volume
control essentially becomes a set-and-forget adjustment.

Happy Holidays, everyone.


73, de John, KD2BD


=====
Visit John on the Web at:

        http://www.qsl.net/kd2bd/


               
__________________________________
Do you Yahoo!?
The all-new My Yahoo! - What will yours do?
http://my.yahoo.com 
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Bill Steffey NY9H]

i just bought some USB to serial port converters... like the one I have
been using for the piles of serial stuff i have.  I have no connection to
this place , other than believing it is a good deal for this group.  8
serials from a USB port.

And they are very configurable... from the edgeport software.
And the batch he just put up are 25$ ...  plus $ 10 shipping,,for 8 ports!!!
I bought some at $35 last week.
He has a stash of them...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=31495&item=6732626527&rd=1

here's the factory
http://www.ionetworks.com/products/usbtoserialconverters/index.jsp

73

bill

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com