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Re: Radio for Radio
To: "CRTech" <crtech@crtech.org>
Subject: Re: Radio for Radio
From: Jim Turvaville <jim@rt66.media>
Date: Mon, 10 Sep 2018 13:06:08 -0700
In-reply-to: <830893665.249995.1536607774559.JavaMail.zimbra@bevcomm.net>
References: <830893665.249995.1536607774559.JavaMail.zimbra@bevcomm.net>
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My experience with car radios for EAS monitoring as well as translator relay use has been great.  A couple of thoughts:

1.  Many new radios have RCA line outputs designed to be plugged into external power amps, which allows us to not connect speakers at all to the unit. Then a simple matchbox can take the unbalanced signal to +4 studio grande balanced audio. 

2.  In absence of the RCA plugs I have used 70-volt transformers to create a better impedance match.  Take the radio outputs and connect to the 8-ohm side and put a 600-ohm load resistor across the 70-volt side and it will typically load just fine and not have notable audio distortion.  Volume out on the radio itself will determine level on the side of the transformer, so adjust carefully. 

3.  Use a good UPS to hold the radio power supply so it will not go off or in standby mode in case of a power blink. 

As always, YMMV!!

Jim "Turbo" Turvaville -  SBE Certified Radio Engineer 
Turbo Technical Services -  www.jimturbo.com 
Route 66 Media - www.rt66.media

---- On Mon, 10 Sep 2018 12:29:34 -0700 Mark Carol Bohnett <mbohnett43@bevcomm.net> wrote ----

Dear Sirs

We have a Full Power site in Minnesota that is fed primarily with a IP based signal.  The emergency back up has been an off-air broadcast receiver but the antenna is only 15ft off the ground, directly in behind a large self supporting tower (lots of grounded steel).  Depending on the day, the signal is fair but never clean.  In fact I have to point my antenna between the steal struts to get any signal. 

If I move the antenna and pole to the other side of the tower, the signal and sound quality is perfect.  The problem is the site is owned by American Tower who charges you for the very air you breath while on site!  We are attempting not to add more monthly costs to a moderately supported signal; therefore, we are searching for an alternative.

I was commissioned to use a "car radio" for a test (and to my surprise) and the audio quality was actually better that the professional receiver. 

Now I have to build a site with a car radio and interface it into the broadcast world.  I have used in the past the Bogen impedance matching transformers.  The spec is 10K input to 600 balanced out.  The speaker output of the radio is 8 ohmn therefore, I am looking for a 8 ohmn to 600 ohmn transformer.  I found the "Classic 119DA" transformer but they are pretty pricey.  Has anyone found (in this same or like situation) some "miracle" cure for matching a car radio into a line level device (preferably without a amplifier in between)?

If not, I'll probably go with the Bogens and hope for the best, but I wanted to see if any one had found a better alternative before I build the site.

Any thoughts would be appreciated.

E. Mark (MN)

Follow-Ups: Re: Radio for Radio
(Willie Barnett <wbradiolists@gmail.com>, 14 Sep 2018 16:41:25 -0000)
References: Radio for Radio
(Mark Carol Bohnett <mbohnett43@bevcomm.net>, 10 Sep 2018 19:29:59 -0000)
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