[Elecraft] K3 and SM-220

Sun Oct 10 19:02:10 EDT 2010

Don't know.  Never had occasion to use or look inside a SM-230.  My 
experience is limited to the SM-220.  Perhaps someone else on this list 
has the info you need.  However, all that being said, it would not 
surprise me if the band-scope option used the same module for both 
units.  If the SM-230 used a module called the BS-8, it is possibly the 
same unit.  If the part number is different, then some more examination 
would be needed.  

Keep in mind, however, how the band scope works.  It is basically an 
electronically tuned receiver that derives its tuning voltage from the 
horizontal sweep oscillator in the band scope - which at root is 
basically an oscilloscope.  The sawtooth signal from the sweep 
oscillator drives a varactor (voltage variable capacitor) diode 
connected to the tank circuit of the BS-8 oscillator.  The oscillator 
then sweeps back and forth around the 8.83 MHz IF, either plus or minus 
20 kHz or plus or minus 100 kHz,  depending on the bandwidth selected.  
The BS-8 oscillator signal is mixed with the 8.83 MHz IF signal from the 
radio, resulting in a new IF (for the band scope only) that is amplified 
and detected, then sent to the SM-220 (or SM-230) vertical amplifier.  
The resulting varying amplitude signal then corresponds  approximately 
to the level of any signals present ,   which then appear as "pips" on 
the spectrum-display screen.  Most all spectrum analyzers work this way, 
at least the "conventional" analog types.  The Elecraft P3 is probably 
rather different in how the detection and display process is 
implemented, but remember it has access to a whole box full of software 
tools that the older SM-220 and SM-230 do not have.

In order for the SM-220 or SM-230 to display signals from the K3, or any 
other transceiver, all that is needed is for the band-scope oscillator 
to be able to sweep back and forth  within the desired offset from the 
transceiver IF, and  for the band-scope unit's "front end" to be able to 
tune to the desired transceiver IF.  Everything else from that point on 
is pretty much independent of  what radio it is connected to .  Some 
band-scope adaptors don't even have a tunable RF front end, instead they 
rely on the transceiver's  signal processing circuits to provide the 
needed selectivity.   

Spectrum analyzers and band scopes are essentially the same animal.  A 
basic display is easy.  The hard part comes when you want precise sweep 
linearity, exact amplitude calibration, and the ability to separate and 
measure "close in" components of modulation products.  Those last items 
are the reason that -hp- (Agilent), and other high end test equipment 
manufacturers can command prices of $15K to $50K for their instruments.  
For example, consider the measurement of a 1.2 GHz FM signal from a data 
transceiver that I work on from time to time.  I happen to have a 
Tektronix spectrum analyzer that will display discrete modulation 
sidebands that are only 50 Hz apart, and measure their exact amplitude 
and frequency offset from the main carrier.    It is however, rather 
bigger than a breadbox,  and it costs a bit more than the SM-220.

- Jim, KL7CC

Radio Amateur N5GE wrote:
> On Sun, 10 Oct 2010 13:58:20 -0800, Jim Wiley <jwiley at alaska.net>
> wrote:
>
> Hello Jim.
>
> I have a Kenwood SM-230.  I wonder if the same holds true for that
> model?
>
> Tom Childers, N5GE
> Licensed since 1976
> QCWA Life Member 35102
>
> n5ge at n5ge.com
> http://www.n5ge.com
> http://www.swotrc.net
>
>   
>> Open up he SM-220.  The band-scope option is in a small metal box toward 
>> the rear of the scope.   It will be marked either BS-8 or BS-5, for 8 
>> MHz or 5 MHz respectively.  It may be possible to retune the unit to the 
>> desired operating range, although it may be necessary to juggle some 
>> component sizes.  A schematic can be obtained on line I think.  Note: if 
>> it is a BS-5, the only difference between the units is the oscillator 
>> coil and a few components.  Replacing the appropriate parts with those 
>> for the alternate frequency range will make the switch.  Since these are 
>> "discrete" parts, the swap should be straightforward.  The 8 MHz version 
>> may have enough tuning range to shift over the K3 IF without changing 
>> parts.  As supplied, the BS-8 is set for use with an 8.83 MHz IF, if I 
>> remember correctly. The band-scope print is part of the main SM-220 
>> manual. .
>>
>>
>> - Jim, KL7CC
>>
>>
>> DM4iM wrote:
>>     
>>> Elecrafters,
>>> i like to interface a Kenwood SM220 Scope to a K3.
>>> There is a Pan Display Option installed, but there is no hint
>>> if it is the BS-5 (3.3Mhz IF) or BS-8 (8.83Mhz IF).
>>> How can i determine which Pan Display i have?
>>> I got this scope from a SK w/o any manuals.
>>> If it is the 8Mhz IF, can i retune it AND will it work with a K3 /
>>> KXV3A ?
>>>
>>>
>>>   
>>>       
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