[NJARC] IRE Alignment

[NICHOLAS SENKER]

Thanks Al, you're a wealth of information.  I don't know what we would do without you!
Nick

----- Original Message -----
From: Al Klase <al at ar88.net>
To: New Jersey Antique Radio Club <njarc at mailman.qth.net>
Sent: Mon, 10 Mar 2008 20:43:49 -0400 (EDT)
Subject: Re: [NJARC] IRE Alignment

Visit our web site - See http://www.njarc.org
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Hi Nick,

The output impedance of the old "Standard-Signal Generators," like the 
General Radio 1001-A, was 10 ohms.  This is not acceptable for critical 
alignment of a broadcast receiver designed to work with a random-wire 
antenna, e.g. and inverted-L maybe 40 feet high and 60 feet long.  The 
solution was the IRE, sometimes called RMA, dummy antenna.  This is a 
network that sits between the generator output and receiver input. 

The generator ground is connected to the receiver ground.  Between the 
generator output and receiver antenna terminal there is a 200pF cap in 
series with a 20mH inductor.  The inductor is shunted by the series 
combination of 400pf and 400 ohms.

The net effect of this is that the generator is connected to the 
receiver by a 200pF cap at frequencies below 2 MHz, and a 400 ohm 
resistor above 2 MHz.  I often just use a 220pF cap for the broadcast 
band and a 390-ohm resistor for the shortwave bands.

All this make a slight difference in the alignment of the input tuned 
circuit.

Al

NICHOLAS SENKER wrote:
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> I have just finished recapping a GE J-71 table radio  and am touching up the alignment.  The procedure (Riders 12-29) calls for a IRE dummy antenna for the RF alignment.  What does this mean?  I just used a loop on my RF generator and this seems to work fine.
> Another interesting thing about this receiver (1940-41 vintage) is that the shortwave bands are dead while the broadcast band works fine.  While recapping I noticed a disconnected wire that was neatly clipped and tucked out of the way.  Reconnecting it to the band switch, I now get SW reception.  I recall a discussion on the Broadcaster about wartime radios having the SW bands  disabled, presumably to limit propaganda?  I think this was one of them?
> Nick Senker
> _______________________________________________
> NJARC mailing list
> NJARC at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/njarc
>
>
>   

-- 
Al Klase - N3FRQ
Flemington, NJ
http://www.skywaves.ar88.net/

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