[Hallicrafters] RTMA Dummy Antenna needed for alignment?

[jeremy-ca]

As Roy mentioned "sensitivity tests" is the magic phrase.

If the input coils were designed for a high impedance antenna and a low 
impedance generator was placed across them then the excessive loading would 
give erroneous readings. You can notice the effect when using a coax fed 
dipole; in many cases the signal drop is rather dramatic.

If the dummy load isnt available, missnamed since it is an early attempt at 
a broadband matching device, isnt available then wind a 9:1 balun on a 
FT50-43 ferrite toroid. The old TV baluns are pretty much useless below 
20MHz if you want accurate readings.

Carl
KM1H


----- Original Message ----- 
From: "Roy Morgan" <k1lky at earthlink.net>
To: <hallicrafters at mailman.qth.net>
Sent: Tuesday, April 29, 2008 12:27 AM
Subject: Re: [Hallicrafters] RTMA Dummy Antenna needed for alignment?


>
> On Apr 28, 2008, at 11:10 PM, Roger D Johnson wrote:
>
>> The whole idea of the dummy antenna was to align the input
>> of the receiver with the "standard" 50 to 100 ft wire
>> antenna most listeners used in the old days that generally  gave .... a 
>> compromise adjustment
>
> There was another reason, also:
>
> At the time the "Standard Dummy Antenna" was defined, there were few 
> standards.  Manufacturers could claim most anything about the  performance 
> of their receivers, and did. Fair comparisons between  receivers could not 
> be made.  In addition, the military was  increasingly specifying the 
> performance of receivers and found there  was no common method of setting 
> up test conditions for sensitivity  acceptance tests.
>
> I think it was in the late 1930's (perhaps 1938) that the predecessor  to 
> the RTMA published the spec.  There was an article in a national  magazine 
> (Perhaps the IEEE journal) that seems to have introduced the  thing, and 
> likely has more information about the thinking at the time.
>
> Roy
>
>
>  Roy Morgan
> k1lky at earthlink.net
> Lovettsville, VA 20180
>
>
>
> ______________________________________________________________