[R-390] [KA9EGW] s/n 4214 preliminary test results

[Roy Morgan]

On Sep 17, 2009, at 5:36 PM, <ka9egw at britewerkz.com> <ka9egw at britewerkz.com 
 > wrote:

> The Measurements 82's setup is pretty self-intuitive.
>
> Test setup: a couple-feet hunk of 18AWG stranded jammed into the  
> center pin
> of the sig/gen's "N" connector and the 390's "C" connector.... much  
> everywhere the set tunes, on every band, there's something to
> hear on such a little wire inside a building...

Not surprised you get signals all over the place.

> Reckon if I want conclusive data I'll need an N-to-BNC adapter  
> [readily
> available] and a C-to-BNC [*frightfully* spendy].  Or SO-239 to N/C.

There is a better way.

> Suggestions?  I'm halfway tempted to rip the "C" for an SO239

UGH.. Don't do that.

That C connector is part of the antenna relay.  here's what you can do:

Get a twinax connector - good ones can be had for 4 or 5 bucks.  Get a  
BNC chassis mount connector.  Ground one pin of the Twinax connector,  
file the BNC down till you can force it into the cable clamp on the  
Twinax one, hook the BNC center pin to the other pin of the Twinax and  
push the BNC into the cable clamp after it's tightened in place.   
Epoxy and a spot of solder will do also.

I bought the right tap and drill (I think it's 3/8-32 or 5/16-32  
thread) to tap the cable clamp ring and have made some very nice  
adapters equivalent to the military adapter that usually costs some  
$25 or more now.  a right angle BNC chassis mount connector makes a  
nice installation and leads the feed coax parallel to the rear of the  
radio.

Oh, I forgot.. a bit of hot glue or epoxy will hold the two twinax  
pins in place - you do need this - or they will push back into the  
connector.. They are normally held in place by the two wires in the  
twin coax.

I will also make an adapter to set the input transformer balance (68  
ohms from the BNC center pin to each of the  twinax pins - balanced  
equal in phase feed.)

One last thought: if you want to be careful about your measurements  
and be assured that you are in the ball park with the numbers you  
arrive at for input voltage, you need to consider the loading of the  
signal generator (it needs 50  ohms at the end of the output cable to  
deliver the calibrated voltage).  You may decide to make an attenuator  
for the input to the radio, such as 50:1 with 50 ohms and one ohm  
resistors, or even 100:1 (50 and half ohm) so you can be sure that the  
input impedance of the radio is not changing the voltage at it's input  
terminals.

Being moderately sure of RF voltage measurements at the microvolt  
level to 5 or 10 percent is feasible for us.  At one percent, you need  
all that Agilent or HP can give you.  Folk who report sensitivity  
levels to three decimal points are fooling themselves and most folks  
who read their reports. NIST can measure RF levels below one percent,  
but it takes a room full of equipment and half a century of experience.

Roy

  Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073
Home: 607-898-3607
Cell: 301-928-7794