[BC] Xmitters at aol.com

Mon Apr 9 08:40:51 CDT 2007

The circuit feeding the telco pair should not be connected as 150 ohms unless
there has been a problem obtaining the required frequency response. This 2:1
reduction in audio level will reduce the S/N (2:1 = 6 dB). Usually noise is the
problem on phone circuits. You are allowed 0 dBm (1 milliwat in 600 ohms)  with
peaks to + 8 dBm. You should use the available headroom and not compromise
it unless a lower Z feed is necessary to help equalize the line.

--
Cheers,
Richard B. Johnson
Read about my book
http://www.AbominableFirebug.com

 -------------- Original message ----------------------
From: "Dana  Puopolo" <dpuopolo at usa.net>
> 111C's also worked great for splitting audio to multiple studios. Years back,
> I connected one winding to the output of a medium powered stereo receiver (a
> Pioneer SX-434), and used the other three windings to distribute air monitor
> to three separate studios. Worked great.
> 
> -D
> 
> ------ Original Message ------
> Received: Mon, 09 Apr 2007 03:06:46 AM EDT
> From: "Milton R Holladay Jr." <miltron at mindspring.com>
> To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
> Subject: Re: [BC] Xmitters at aol.com
> 
> According to Bell System practice, part of your second paragraph is not
> precisely correct.  The pair of windings that go to the line should be wired
> in parallel on both ends, to help overcome the line capacitance.
> A specific set of the windings is designated LINE (I believe it is 1 & 2 and
> 5 & 6) and the other set is designated DROP (3 & 4 and 7 & 8  ?)and is wired
> 600/series or 150/parallel to match the customer's needs. This is the case
> no matter which end of the circuit it is on.
> This arrangement should be flat to 15,000Hz for a quarter mile or more,
> depending on cable type; maybe several miles if you had old timey open wire
> lines.
> The 23A was the equalizer for 8kHz, and the 16816 for 5, 8, & 15 kHz,
> succeeded by the 20159
> I believe Barry has official data posted for at laest the 111C.  I have seen
> one old one in a cast iron case...................
> M
> ----- Original Message ----- 
> From: <RichardBJohnson at comcast.net>
> To: "Broadcasters' Mailing List" <broadcast at radiolists.net>;
> <broadcast at radiolists.net>
> Cc: <RLO2L at aol.com>
> Sent: Friday, April 06, 2007 9:37 AM
> Subject: Re: [BC] Xmitters at aol.com
> 
> 
> >
> > The telco 111-C "repeat coils" are available on the surplus market. They
> are probably the finest audio-frequency transformers --ever. They have four
> shielded coils and the core is a toriod made of mu-metal strip. Very
> impressive for something designed in the 1920s. The companion shunt
> equalizers are also available although I don't remember the number. They
> consist of a tapped inductor and tapped series resistors. Basically, you
> shunt-out
> > the low frequencies the same amount as the high frequencies have been
> shunted-out by the line capacitance. A one-mile long physical pair, with no
> side-legs or stubs can be equalized to over 100 kHz, so equalizing it to 15
> kHz is a no-brainer. You won't need any amplification, the line-loss after
> equalization will be less than 10 dB.
> >
> > You connect your  station's audio feed at the studio to the outgoing 111-C
> "coil" primary. You make the primary by connecting any two coils in series.
> You connect the other two series-connected coils to the phone line. At the
> transmitter, you connect another "coil" the same way. On the telco side, you
> connect will your shunt equalizer but don't connect it yet. Since you
> probably don't have a helper at the studio, you go to the studio and send 15
> kHz. You go back to the transmitter and measure the signal, it will probably
> be about 9 dB below  what you are sending from the studio. Write this down!
> Then you go back to the studio and send the exact same level at 100 Hz. Then
> you go to the transmitter and connect the equalizer. You leave the resistor
> in its default (mid) position, and you adjust the taps on the inductor to
> reduce the 100 Hz level to the level of the 15 kHz tone previously measured
> and written down. You should be able to get it within 1 dB.
> >
> > The result will be an equalized "program channel A," in telco lingo. For a
> mile-long line, you will certainly
> > have it equalized well enough for AM, perhaps even FM. In a previous life
> I was able to equalize stereo pairs to 15 kHz, although I needed a Langevin
> EQ-257-A  equalizer. It had a multi-turn wirewound potentiometer in series
> with
> > the inductor.
> >
> > --
> > Cheers,
> > Richard B. Johnson
> > Read about my book
> > http://www.AbominableFirebug.com
> 
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