RFI / Computer Software

KD5TTZ · Post by **KD5TTZ** » Fri Jul 20, 2007 5:54 am

Hey Gang,
I was doing a little experiment with my audio.
I was trying to use Adobe Audition 2.0 to create some VooDoo, Now with the ASIO sound card there is no latency so the DriectX and VST real time fx work pretty good. Like I said just an experiment.

So all this connected to the head phones sound awesomely great, but when I monitored from the radio(connected to the dummy load) I get an enormous amount of RFI. At that time I wasn't running any amplifier.

I am trying to figure out what was causing the RFI, could it be that the radio (Kenwood TS-2000) is just not going to work with VooDoo?

Or could it be the the computer getting RFI?

If anyone could shed any light on this subject, please do.

Thanks,
God Bless,
KD5TTZ

w5cul · Post by **w5cul** » Fri Jul 20, 2007 4:46 pm

Are you using a shielded cable to pass audio from the computer to the radio? Is there an isolation transformer installed between the two? Or, less expensively, is the cable wrapped several times around a ferrite core? All of these will help in eliminating RFI problems in the audio. When I had my Mark V connected to the computer sound card for recording and playback, I had to run both the transmit and receive audio through a couple of Jensen 1:1 transformers to clean up the induced trash. Hope this helps.

Post by **Voodoo Guru** » Sat Jul 21, 2007 3:36 am

Yes, Mike has hit upon the best solution for the RFI problem in the Computer.
We had to do similar things here.
The problem area here was that the RFI was getting in thru the Keyboard.
The solution was to add several 'snap-it' mix 31 ferrite cores to the keyboard cable.
We then also added it to the rest of the I/O cables for good preventative measure.
Fixed the problem

God Bless!

KD5TTZ · Post by **KD5TTZ** » Sat Jul 21, 2007 11:34 am

Good Answer,
But I use a wireless keyboard and mouse.

Any other ideas?

Thanks,
Kyp

Post by **w5udx** » Mon Jul 23, 2007 4:33 am

Kyp,

The first question is, Do you have RF in your shack without the computer hooked to the radio?

I would try and isolate the RF first on the coax coming into the shack, if you haven't done so already.

I.C.E. and some line isolators should do the trick, If you have done all of those things already,

it could be coming thru the AC into the power supply on the computer, you might try and isolate it from the wall.

Tripplite makes a good isolation power strip/box that works great for this at my house.

Just some other ideas to combat RF. Gotta luv it.

Post by **Voodoo Guru** » Mon Jul 23, 2007 5:55 am

Good Answer,
But I use a wireless keyboard and mouse.

Well, there is usually a receiver with some wires on it going to the computer.
We had one here before that we had to put ferrite on.
Good answer from Greg too!
Man.....guess you must be some kind of board with hammy radio to be on here posting!!!
Great to see ya!

KD5TTZ · Post by **KD5TTZ** » Mon Jul 23, 2007 9:15 am

I have been trying to get the VooDoo for a while now. I have the equipment to do the job. It just seems like what ever I do I get RF into what ever I am using.

No I did not get the I.C.E as of yet. It is in the making.

I was just thinking that into the dummy load at 25 watts should not produce any RF, but I guess I was wrong.

I am currently going through some life changing events that prohibit me from purchasing anything at this time. So if I don't have it, I probably wont be getting it for a while.

So if you guys have any home brew ideas, send them this way, I would appreciate it.

God Bless,
Kyp

!KANT · Post by **!KANT** » Wed Jul 25, 2007 2:07 pm

Well one of the first things I thought of [instead of the usual] was whether or not the PC was purchased (prebuilt) or homebrewed. In some cases, which I have experienced myself, is that cheap motherboards can be most notorious for RFI susceptibility.

BUT!!!.....

Seeing that you have RFI with low power with a DUMMY LOAD--which I have experienced also--sounds like POOR isolation [as Mike mentioned]. The best remedy IS the isolation transformer. Believe it or not you should try one of the cheap car audio isolators--yes, their intent is to eliminate ground loops to eradicate HUM.....but it'll do the same thing. And at $5 - $10 on eBay or your local car audio outlets it's a minor investment that you can try.

The Line Isolators [Greg mentioned] I use here and those have eliminated RFI to the home theater--too bad it took me a while to understand where to place it in the transmit chain.

!KANT · Post by **!KANT** » Wed Jul 25, 2007 2:10 pm

Well one of the first things I thought of [instead of the usual] was whether or not the PC was purchased (prebuilt) or homebrewed. In some cases, which I have experienced myself, is that cheap motherboards can be most notorious for RFI susceptibility.

BUT!!!.....

Seeing that you have RFI with low power with a DUMMY LOAD--which I have experienced also--sounds like POOR isolation [as Mike mentioned]. The best remedy IS the isolation transformer. Believe it or not you should try one of the cheap car audio isolators--yes, their intent is to eliminate ground loops to eradicate HUM.....but it'll do the same thing. And at $5 - $10 on eBay or your local car audio outlets it's a minor investment that you can try.

I use a RadioWorks Line Isolator and those have eliminated RFI to the home theater--too bad it took me a while to understand where to place it in the transmit chain.

KD5TTZ · Post by **KD5TTZ** » Wed Jul 25, 2007 2:38 pm

The PC was built. I purchased all the best parts that I could get. (At the time)

Check out this page. http://www.sm5cki.se/rw%20t5g/index.htm

This page also. http://www.airmail2000.com/rfi.htm

Do I need an isolator between each item? Like out of the radio to the tuner and to the final? Also the audio line insulator as well. Should I use these everywhere that I can connect one?

I will try to build one, I can not buy one at this time.

God Bless All.
Kyp

KD5TTZ · Post by **KD5TTZ** » Fri Jul 27, 2007 8:41 am

I am looking at the TRIAD TY-144P, and the TRIAD TY-146P Transformers. How would any of you rate the 144 to the 146.
I can get the 144's for 3.25 each and the 146 for 5.00. Anyone know where I can get them cheaper? This is from a supply house here in Alexandria.

God Bless.

Kyp

w5cul · Post by **w5cul** » Thu Aug 02, 2007 10:13 pm

Kyp,

You may want to rethink the transformer choices you have made. Here are a couple of hyper-links that will take you to data sheets detailing the transformers. Pay close attention to the "Frequency Response", as well as the "Total Harmonic Distortion" parameter. The lower and upper bound frequencies they list usually indicates the audio bandpass they are capable of passing. Unfortunately, they start at 200Hz.

http://www.alliedelec.com/Images/Produc ... Y-144P.pdf

http://www.alliedelec.com/Images/Produc ... Y-146P.pdf

w5cul · Post by **w5cul** » Thu Aug 02, 2007 10:29 pm

Kyp,

I was just thinking that into the dummy load at 25 watts should not produce any RF, but I guess I was wrong.

This is a good indicator that you have some grounding issues, like no or very poor ground for completing the circuit. The circuit being RF out to dummy load via the center of the SO-239, returning to ground through the ground shield of the cable heading for the station ground point. What kind of Ground system do you have in place? Also, are you sure that all of your audio cables are internally wired properly? That alone can definitely cause RFI in your audio at low power levels.

I think if you use the I.C.E device, that will keep RF from entering the shack via the coax heading for the antenna. I have mine jumpered between the amp and the standalone antenna tuner/selector, using the station ground point as a mounting point. Seems to work very well.

w5cul · Post by **w5cul** » Sun Aug 05, 2007 2:42 pm

Kyp,

I have been improving some of my old audio projects today, going to smaller form factors, and I ran across the transformers that I used to interface the audio rack into the computer. I used Jensen JT-11-FLCF transformers. They run about $37 minus shipping. I know that is more than you budgeted for, but, the data sheet for this transformer will give you an idea of the specifications that you are looking for. These guys are flat from 20Hz to 20Khz. Kind of over kill on the high end of the audio bandpass for our application, but exceptional transformers none of the less. I also ran across an old project box that I mounted a Jensen JT-DB-E 12:1 transformer. This was used to directly interface the audio rack gear right into the MIC jack of the Mark V prior to me tapping the balanced modulator. It is a step down transformer that will take the line level audio coming from the rack gear down to a MIC level that the radio's MIC jack calls for. Without something similar, if you were to interface the rack gear directly into the MIC jack, you would have a strong possibility of overdriving the MIC amplifier in the radio, as well as pickup AC hum and RFI. Either of these setups can be wired for any radio, Kenwood, ICOM, Yaesu...etc.

Just thought I would pass that info along.

Take care,

KD5TTZ · Post by **KD5TTZ** » Tue Aug 21, 2007 5:56 am

Well guys,
I am off to a new job.
I am heading off shore with a company by the name of Enterprise.
I am an I&E tech by trade, and just couldn't resist the $$$$$$$ offer any longer. Its a 14/14 so I will have plenty of time to get projects finished.

I hope to at least have echo link up while I am out there.

You guys take care, and I will be hearing ya in a few weeks, I am leaving out this week for orientation (5 days) then on the 29th for a 14 day tour.

God Bless,
Talk to yall soon.
Kyp

w5cul · Post by **w5cul** » Tue Aug 21, 2007 7:53 am

Kyp,

Alrighty, look forward to talking with ya during your breaks. You be careful out there!!

Take care,

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RFI / Computer Software

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