TS-850 Direct Injection questions

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wannavoodoo
Audio Head
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Joined: Tue Sep 17, 2013 2:05 pm

TS-850 Direct Injection questions

Post by wannavoodoo » Thu May 01, 2014 7:36 pm

I modified my TS-850 for Direct Injected AM audio as per KA0KA's website http://www.ka0ka.com/am_mods.html.

I ran an audio patch cable between IC3 on the underside of the IF board and connected it to the RTTY port on the back of the radio. I disconnected the previous RTTY circuit and used a 4.7 ohm coupling capacitor just like the instructions on the above website.

I know its advised to use a Jensen Isolation Transformer but I don't have one yet. I'm curious why when I try to run audio from my Xenyx 802 mixer from its main TRS unbalanced line out to the direct injection port on my TS-850 the resulting audio is very thin/distorted sounding?

Is it absolutely necessary to use a transformer to fix the impedance mismatch between pro audio gear (low impedance) and the balanced modulator (high impedance) to get decent sounding audio with an 850 direct injected?

I've seen countless videos and posts of people who recommend hooking up a mixer like my 802 straight to the ACC/ACC2 jack on the back of whatever radio. I'm assuming piping audio into the ACC port is comparable to going straight to the balanced modulator IC.

I intend to buy the transformer (was thinking it was more for RF/HUM avoidance) but am curious if not having is why I can't even get halfway decent transmit audio out of my 850 or if I have something else wrong. I have double checked my 4.7 ohm coupling capacitor's polarity and the connections as per KA0KA's website.

Any input would be appreciated.

wannavoodoo
Audio Head
Posts: 8
Joined: Tue Sep 17, 2013 2:05 pm

Post by wannavoodoo » Thu May 01, 2014 7:49 pm

I just switched to SSB and plugged in headphones to hear what the TX monitor sounded like with the direct injection using LSB and it sounds fantastic.

I wonder why SSB would work OK with this setup and AM would not?

Still digging...

wannavoodoo
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Posts: 8
Joined: Tue Sep 17, 2013 2:05 pm

Post by wannavoodoo » Sat May 03, 2014 11:04 am

On a whim I decided to plug in my SDR dongle to the PC to use to monitor my TS-850's AM transmission instead of my Drake R8A.

I actually sound just fine on AM. Very wide in fact pretty respectable with just the Xenyx 802 and dynamic mic plugged in.

No idea why the Drake was picking up my AM audio so horribly, I've always used it on the bench as a monitor radio with whatever I was transmitting on.

So... I'd say I've got voodoo AM and if I can find an Inrad #475 or if a DSP-100 landed in my lap for reasonable money (hah!) I'll have some voodoo SSB too.

Now time to build a decent audio chain...

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Post by Voodoo Guru » Mon May 05, 2014 1:39 am

Howdy wannavoodoo,

Sorry we haven't responded sooner but were in the middle of moving and time is short for sure.

You have hit upon all the suggestions that we would have suggested, especially with listening to the AM Signal with an off air monitor that can receive the bandwidth your transmitting.

A transformer is not absolutely necessary and the 4.7uf Cap will work just fine. The transformer just gives you more isolation and a better match.

It is great to still hear of people experimenting and modifying their rigs. This is what it is all about, getting in there and having fun!!

Take care,
Voodoo Guru
From Deep in the IDD of the Sub-Harmonix Realm

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