Mixing the radios Part 2

 

The other day, I mentioned that I'd brought this Audio Telex TX8000 mixer. It's as old as the hills. 

You can see on the top left some markings.. and if you look really carefully you can see spots all over the front of it. 

I received it yesterday and quickly found this to be paint (or something). A few minutes with metho and a rag, and I was able to clean the front fascia up good as new. 

After the clean up, I installed it under the radios. I really haven't done any testing - just straight in to see what happened. The IC706 and G90 being the first connected. The XLR output goes to the mic input on my Xenyx 302USB mixer to mix it with my PC audio and out to the speakers. 

Everything works as expected. Bonus. 

The IC706 has always had a fair old hum going on - my speaker setup has a subwoofer and it's wound up a fair way (bass guitar player.. I tend to like feeling sound). The addition of this mixer certainly boosted the signal a bit, bringing the hum along for the ride. A quick adjustment of that channels bass control though whilst listening to some stations having a QSO, allowed me to drop the bass down enough to get that hum down without drastically impacting the sound quality. I took the top off the treble while I was at it, which made some difference to how tolerable the static is. 

The ongoing problem I have is interference to my PC audio when I TX from the IC706. It seems to be going via the audio from my PC into the Xenyx mixer. If I disconnect that cable whilst TXing, it goes away. 

Unfortunately due to my cabling setup, the audio cable runs behind the radios to a wall socket. I tried a few turns of the cable through a toroid near the desk without much success. I think my next attempt will be to pull the cable out so I can see its path, and get as much of it through a toroid at the back of the radio as I can and see if that helps. 

It's by no means the end of the world, and it's only the IC706 that does it. The G90 doesn't cause the same problem on either antenna, and they're both pushing the same power out.

In other news...

On the subject of mixing.. I recently posted about isolation between the antenna switches. 

An observation I've made since I moved to the 4 switch setup is how utterly capable of receiving my G90 is even though it's set to a position with no antenna. If set on an FT8 busy band, the waterfall will halve.. but will still receive plenty of signals.  Unless I set the switch on the antenna that isn't being used for TX to an empty position this continues. 

It's become a necessity - when I first set it up, harmonics excepted, I could generally TX on the IC706 and have the G90 on another band without much drama. Now it's overloading regardless of band - it's not obnoxiously bad (ie the signal isn't angry red), but it's steamrolling through whatever the G90 is set to with a pretty solid signal. This means I'm stuck effectively cutting off the G90 every time I use the IC706.

The only other thing I really haven't ruled out is that these all use a common earth given that the feedlines are mounted on the same strip of aluminium. 

When I'm feeling a little healthier (my sinuses have been giving me grief), I might try bypassing the switch boxes and see if the behaviour is improved. I won't be able to help needing to keep the radios on different bands given the proximity of the antennas, but if I can stop the IC706 interfering with everything, we'll call that good. 

I was trying to avoid doing that until I get hold of an IC7300. I really wanted to have a pair of fully capable radios to mitigate the need for jumping between antennas. I do however need new glasses - the Specsavers version of $200 glasses that most peoples health insurance covers usually still turn into $600 pairs for me. The second pair "free" is anything but if I want to make them wearable. I also desperately need new tyres. Once these are all paid for, that might become something of a possibility.