[R-1051] 1051 Audio conections

[Ray Fantini]

The two line audio outputs of the 1051 family of radios are very clean and flat response when terminated into a 600 Ohm load. Have to remember that this same radio was used in early digital and Fax circuts so response was a key issue. Biggest problem is that in most applications of using the radio people have no idea about connecting a low impedance balanced source to a high impedance load like the unbalanced input to a computer sound card. What's worse is that almost all of the consumer junk that's available these days has audio output and a microphone level input and not a line input so unless you use an attenuator you will over drive the input to the computer and drive it into distortion. The more expensive class of workstations or systems with standalone audio cards tend to have line level inputs and many external professional audio interfaces will support 600 Ohm balanced inputs. Beranger has several USB supported audio devices that are under $100 but one of my favorite cards right now is the plane old Creative Labs Sound Blaster Audigy Fx PCIe Sound Card, supports line input and output including 600 Ohm and will sample in 24 bit resolution at 192 KHz along with supporting a signal to noise ratio in excess of 106 Db, not a bad card for about $40

Ray F

-----Original Message-----
From: R-1051 [mailto:r-1051-bounces at mailman.qth.net] On Behalf Of Nick England
Sent: Sunday, November 09, 2014 12:33 PM
To: R-1051 Discussion Group; stevehobensack at hotmail.com
Subject: Re: [R-1051] Back Panel Plug Diagram

I went looking at the schematic and probably the easiest place to tap is at the top of the line level control - the signal at that point is directly out of the product detector (in SSB/ISB) and also the AM detector (via just an emitter follower from the detector diode). Or you could pick up that same point under the chassis on the module connector.

*Oh wait! - I apologize - I missed the xmtr sidetone connection on the rear at J4-Y (USB/AM) or J4-X (LSB) - that signal goes to the same point in the audio chain (through a 15uf cap). It is "intended" to be an input, but there's no reason you can't use it as an output.*

As Ray says, the mechanical filters in the IF chain will probably be a limiting factor (although there is some feedback in the audio line drivers that might further shape their freq response). The AM filter is listed as FSN 526-9421-00 Collins F 500 Y 70 AM - so 7 kc wide rather than the 8 or
16 in your R-390A. let us know how it works!

Apologies if I am repeating stuff that "everyone knows"- I am new to the
R-1051 and just started to explore the circuitry.

Cheers,
Nick England K4NYW
www.navy-radio.com