[Kenwood] SM-220 question

[Bryan Swadener]

Hi Ron,
 
Unfortunately, most recent transceivers use a "Roofing Filter" that limits bandwidth to +/- 10 or 20 KHz.  That limits how far up/down from your receive frequency you can see with a bandscope (nee Pan Adapter or Spectrum Analyzer).  Fortunately, my TS-850's design still has a Roofing Filter but doesn't limit the bandwidth at the output. It's as wide as the bandpass filter on the rcvr frontend.  So far as I've seen, MOST rigs fit the previous description.
 
The SM-220's function as a Pan Adapter isn't all that good.  The sweep oscillator in the BS-5 (3395 KHz IF) or BS-8 (8830 KHz IF) drifts badly, the CRT's generic graticule doesn't work well for an SA (Spectrum Analyzer), and the low persistence phosphor of the tiny 3" CRT often misses short-duration signals such as SSB and CW.  Then, to make mattes worse, to use it as a xmtr monitor and Pan Adapter requires turning knobs to toggle between modes.  That is a major PITA.  As a xmtr monitor, it doesn't have triggered sweep.  The trace is there unless/until you turn down the intensity.  The SM-220 is OK at one or the other but not both functions.
 
All of this is why I prefer to use my inexpensive Tek 2236 'scope (with larger CRT + triggered sweep) as a xmtr monitor and Heath SB-620 (or Advantest R4131B) as a Pan Adapter. That is, until I can afford Larry N8LP's LP-500 Digital Station Monitor and LP-Pan (about a kilobuck for both).
 
So yes, the SM220 will work as a transmitter monitor as-is (just not that well).  The good news is, you can sell it for LOTSA money and put that money toward something that works better. Or just have it on your desk as a "Blonde Unit" (just for show). That's how I "use" mine.
 
vy 73,
Bryan WA7PRC

> ----- Original Message -----
> From: rbig <rbig at cox.net>
> To: kenwood at mailman.qth.net
> Sent: Mon, 21 Jan 2013 00:19:35 -0000 (UTC)
> Subject: [Kenwood] SM-220 question
>
> I have a nice SM-220 lurking back in the closet.   I think it's time for it to get out and on my desk.   My problem is I know little about the signal monitor.
>
> Let's start with trapezoid.   WIth it all hooked up, I thought maybe you could monitor you xcvr as well as final trapezoids.
>
> 1.  However, I see that if you don't use your final, it somehow has a trapezoid that is "meaningless"  I'm not sure how this all works, but is in fact the trapezoid of your xcvr only really meaningless?
> If so, It wouldn't be of any use to me displaying it.  The final trapezoid yes; the xcvr trapezoid no.
>
> 2.  I can just add the two tone connection to the mike on my xcvr, and see those patterns.
>
> 3.  Not sure of control setting, but there is another way to get voice patterns as you talk----lot's of squiggly lines jumping up and down.
>
> The reason I'm asking this, is because I think we can do some things with it being in place, and no changes added in.  Just park it on the desk, and use it without adding anything.
>
> 73 de Ron, K5BDJ