[Hallicrafters] RTMA Dummy Antenna needed for alignment?

[lrlayton at cox.net]

The SAMS photofact alignment instructions for my SX-42 describe the RTMA dummy antenna as a 200MMFD cap in series with a  20uh choke. The RF choke is shunted by a 400 MMFD cap in series with a 400 ohm carbon resistor.

This same circuit is is shown in my copy of the RCA Radiotron Designers Handbook 4th edition, with values recommended to be within 10 percent of those listed.

I made up a small metal box with this circuit inside  years ago and have used it to align my SX-42 as well as many other receivers with good results. I would avoid the TV balun as most will attenuate  HF signals.

Les Layton
Las vegas, NV




---- Randy Perkins <w5kcm at sbcglobal.net> wrote: 
> Please disregard my posting about the RTMA dummy antenna. With some 
> additional searching the archives, I was able to locate where it looks 
> like I can use an old TV balun and get good results. Thanks & 73, Randy, 
> W5KCM
> 
> Randy Perkins wrote:
> > Hello to the group.
> > I am in the process of restoring my SX-99 receiver. In the alignment 
> > instructions they speak about using this RTMA Dummy Antenna in between 
> > the signal generator and the antenna input terminal.  In the 
> > Hallicrafters SX-99 book it shows the schematic for this Dummy Antenna 
> > and also in the Sams Photofact for the SX-99. The Hallicrafters book 
> > shows the inductor in this circuit to be 20 microfarad in the Sams 
> > photofact it shows it to be 20 millifarad. Does anyone know the correct 
> > value for this inductor?
> > Is this RTMA dummy load actually necessary? How critical are the 
> > component values? What is this RTMA Dummy Antenna for? Digging through 
> > the junk box, I have found the resistor and capacitors or pretty close. 
> > If the inductor is 20 microfarad would some small enameled wire about 1 
> > ohm resistance wound on a small form suffice? Any info on this is 
> > appreciated.
> > 73, Randy, W5KCM
> > ______________________________________________________________
> > 
> ______________________________________________________________