Talkback through my ferrite beads?

[Cutlass327]

A quick description of my setup. Galaxy 939 with a Galaxy DX88HL, strapped together with steel strap, mounted on the "bottom" of a milk crate on its side. A Superstar 400 AB1 class amp mounted to the "top" of the crate above the 2 radios. Using a separate D104 Silver Eagle for each. I have a Powermax 100A power supply bolted to the back of the 2-drawer filing cabinet this setup is setting on. I use 8ga cable for power/ground for the amp, and it feeds a 8 slot fuse block that the radio powers are connected to.

I have been chasing a whine in the 939, and it is affected by turning the 88 on or off. It will start with the 88 on or off, and it is random. If 88 is off, and whine starts, I turn 88 on, it stops but comes back immediately after I turn it back off. Or, vise versa on the 88.. During this time, I have been installing ferrite beads on power cords, antenna coax, etc to see if it would change. Well, just so happens that it didn't make a bit of difference, BUT, I started getting a "talkback" when I had the amp on. I have looked off and on over the past week to track it down, and tonight I just happened to be moving the power cables around (I had strapped them together to tidy them up while adding beads) and I felt a bead buzz. I put it to my ear, keyed up, and heard myself thru 2 of the beads on the 8ga amp power cord and on the main power to the terminal block everything branches from.

Why would these beads be vibrating? In the Q/A section of the page on Amazon, someone said they measured them to be closest to a type 43:

I was unable to definitively determine what mix these ferrite "snap-its" were. My best guess is they are mix 43. They do not appear to be any of the following mixes : 31, 46, 61, or 75. I made the following measurements using an MFJ-269 antenna analyzer connected to a single square turn of 16 ga hookup wire through the ferrite. I tried to make the leads as short as practical. The results were not that impressive which matched my impression of the performance for my application when I used them. Anyway, here are the measurements. I hope they are of benefit to someone. I can neither confirm nor condemn suitability of this product for any particular purpose.
Freq(MHz) R X Z (magnitudeohms and angledeg)
1.8 0 j9 9/_ 90
3.6 4 j16 16.5/_ 75.8
7.2 11 j28 30/_ 68.9
14.4 26 j45 52/_ 59.9
25.8 49 j62 79/_ 51.7
28.8 53 j63 82/_ 50.0
36.0 72 j72 101/_ 45.0
100.0 143 j49 151/_ 18.9
So, based on the numbers above, the best match appears to be mix 43.

Amazon product ASIN B00MFCD56C

 

[543_Dallas]

A lot of amps don't have enough filtering to keep RF off the positive power cable.

Do you have the positive and negative ran through the same bead? If not try running both + & - through the same ferrite. Preferably a large donut with several wraps as close to the piece of equipment as possible. When on one cable only the dc current can saturate the core.

I'm not sure about the number you have. I've always went by the manufacturers datasheet and had good luck.

 

[Redbeard U812]

Good info there. Thanks. Been chasing unwanted talk back myself. Will look for ferrite doing the shimmy.

 

[Cutlass327]

The bead I was using is the one on the right. These are the 3 I have currently available.

I had just the one on the positive only. Would there be any gain in having a ferrite on it? or would I just be wasting time/money?

Also a picture of my setup I was trying to describe.

 

[Cutlass327]

The ring one and the 8ga cable I am using for power

 

[S&W357]

I like that milk crate rig. Good looking & neat.

 

[Cutlass327]

It's nice, because if I need to move it, I just have to disconnect the main line to the antenna and unplug the Anderson connector from the power supply and it is completely disconnected. I have a couple grp31 commercial batteries I have a pigtail for if I really need mobile for some reason, or if the power is out.

 

[Cutlass327]

OK. Here's an observation I just accidentally discovered. The aftermarket power cords for both Galaxies have fuses in power and ground side. Both radios had the ground 4A fuse blown. The only way they were grounding was thru the antenna shield from the amp. How much of that squeals and whistles do you think would have been from that? Would that cause more feedback from the mike on key-up when the amp is on?

What size fuses should there be in these cords for the power and ground side?

 

[Redbeard U812]

Something I did was use a separate ground system. All components get grounded to a common ground. Out to a ground rod. Did that and alot of my static/ hash rf dropped.

I do this in my truck also.

 

[Cutlass327]

I have a 5/16" stud terminal for each B+ and B-, and then a fuse block and a ground bus for the smaller cords connected to those by 8ga wire. Main feed, amp, fuse/ground blocks are connected to the 5/16 studs. The main power goes thru a 100A relay before the terminal so I can power it all off when not in use.