Remote Rig
RRC 1258 Support in English => General discussion forum => Topic started by: nocturnal_transmission on 2013-06-03, 00:56:49
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Hello:
I was unable to find an answer on this. I need to send receiver discriminator audio over the RRC-1258 MKII using the audio input; my discriminator output impedance is likely 5k to 10k ohms, ~200mv. However, the 50-ohm input impedance of the 1258 is loading it way down, and I cannot get an adequate level out the far end. The CODEC input gain does not help enough, but I am also finding that the 1258's noise level rises with the gain, so the S/N remains unchanged.
There does not seem to be a schematic for the 1258 for general use (although there are interface instructions for specific use cases - which is great).
I figured there would be a simple jumper for HI/LOW input impedance , but I may have to remove resistors instead? Is there an jumper setting for this?
Where to I find the specifications for input/output level ranges?
Surely the analog and digital input and output circuits schems are available?
Update 1: Schematics found in the back of manual. The Tip to sleeve DC impedance reads 50 ohms; but the ring to sleeve is very high - so possibly the second channel is high-Z. There are two larger 100 ohm surface mount resistors in parallel that provide the 50 ohms on the tip line. Those appear easy to remove if needed.
Update 2 (final): Mine is NOT an (s) (dual channel version). I am hosed as I need both channels (the other for squelched audio). But this is a good page to determine your model:
http://www.remoterig.com/wp/?page_id=1395
As was noted in a another post, R82 and R137, R102 and R103 can be removed (these existing only in the S versions) to raise the "speaker" input resistance to about 1K, instead of the original 50 ohms. This might be enough, but 1k is still low IMHO. I may have to increase the remaining voltage divider resistors (which total 1K ohm) with another higher value set.
It would be nice to have a jumper setting for 50 ohm / ~10k ohm, for each input channel on the (s) version.
Also - still looking for a product like this one with audio input level controls (on the board), selectable de-emph settings (and impedance).
Thanks!
Greg
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I think the schematics show the audio input circuitry.
I was faced with a similar problem, and although it would have been easy enough to remove the resistors I decided to build a small audio amplifier instead Has been working fine for a a long while now.
73 Roger
VE3ZI
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Ho Roger:
I stand corrected! Found the schematics way in the rear of manual; both inputs should have 50 ohms Z, but one is either open or high-Z, and I never found the second set of 100 ohm resistors on the board. Investigating further.
Greg
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There are only 4 big 100 ohms resistor on the pcb. If you only have 2 resistors you have an earlier version with a single channel codec. The audio interface is built to match 99% of the needs but as written in the earlier posts you can by removing the resistors incrase the imput impedance, if you remove the decoupling cap on the input and put a new one direct to your source you get very high input imepdance.
73 de mike
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Hi Mike:
Excellent idea - I can just open C82 and run the audio right into the amplifier's input (with a new DC-blocking cap), bypassing the input resistors.
Is there a capacitor on the ring input (schematic does not show this)?
Greg
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yes C132
/mike