[AMRadio] Using Heath SB 610 Monitor Scopeto monitor modulationonAM transmitter

[Jim Wilhite]

Ron, I suggest you hook the monitor scope to the grid of the 1st. IF 
tube.  The reasoning behind this is non-linearity is reduced to some 
extent.  I had a hookup to my receiver one time and when people found 
out they wanted reports on their envelope.  Well there are many things 
that will affect that pattern.  The SB 614 I owned had some 60 cycle hum 
in it and it is very difficult to get out.  If you notice in the manual 
of the 614 Heath said to put an RCA plug with a very short piece of wire 
attached from the center pin to ground into the Vertical Input jack. 
The purpose is to eliminate any 60 cycle pickup and introducing 
additional distortion on the displayed pattern.

So after a couple of times of people wanting reports, I disconnected it 
to keep from trying to explain what I was seeing.  Most people wanted 
quality reports and I wasn't comfortable explaining that what I saw 
might not be what they were transmitting.  To be accurate you need to 
check the linearity of all the stages preceding the attach point.  If 
you seen much, be hesitant about giving reports.  This hook up is kind 
of all right for baseline reports but the linearity of the received wave 
will be affected by the distortion you have in your receiver.  If the 
distortion is low, you are good to go, if it is high then you won't be 
telling the guy the entire picture.

Get a distortion analyzer and check your receiver to get an estimate of 
how much distortion is present before you get to technical.  Don/K4KYV 
found some problems with his HO 10 and had to modify it to correct the 
problems.  He might explain which would help you.

Jim/W5JO




> Thanks Jim
>
> You make excellent and insight points as always.  I have encountered 
> the
> issues you speak about in interfacing my 610's with various vintage
> receivers like my NC-300 and 75A4.
>
> Thank goodness that I stumbled across small 455Khz and other 
> frequencies
> "IF" cans at Antique Electronics Supply in Phoenix.  With some minor 
> surgery
> both 610's are monitoring received signals on my receivers.  On the 
> NC-300 I
> went directly to the plate of the 2nd IF and coupled it through a 5PF 
> mica.
>
> On the 75A4 I went to the grid of the 2nd detector tube and used 4.3 
> PF
> mica.   Both have full deflection and ad a bit of "fun" to monitoring 
> by
> being able to see the everyone's signal.
>
> But then, it has been mentioned from time to time that I am "a tad"
> obsessive about these beautiful old boat anchors.
>
> Cheers my friend
>
> Ron Weaver   W6OM