Dealing with RF in the Shack

[@ouijim]

Heil Pro7 headset on ICOM IC-718 had feedback on headset audio cable, eliminated with ferrite ring. Using ferrite and RF Chokes all around shack and portable as needed. Newest Antenna is TRUELADDERLINE Doublet 44 feet with Balun Designs 4114 4:1 Balun, LDG tuner, works like a charm.

[@n4hnhradio]

I love me a doublet. That’s why I have two. The ZS6BKW is in the doublet family, though not a doublet in the strictest sense. My 160m doublet has the gain of a Yagi; I just can’t rotate it. 73, de N4HNH

[@ouijim]

@@n4hnhradio Noticed you live in Suwanee GA . My dad was born in Suwanee, relatives around Buford. Dad's buried in Whitehall : ( I miss Georgia, as I remember, dirt roads, woods, pine trees, peaches, scuppernong grapes, country breakfast at grandparent's home ; )

[@n4hnhradio]

It’s very grown up now. I can’t find a dirt road anymore. But we still have good breakfasts and other foods…and pine trees. 73, de N4HNH

[@Larry-AK0Z]

I have an EFHW antenna and a 5 ferrite chokes on a pigtail between the end of my coax and into the antenna feed point. I don't have any radials or grounds on the antenna or radio and I have no RF in the shack. I work the world and break pileups. 100 watts.

[@n4hnhradio]

100W can be very effective with a dipole and good propagation.

[@thuff3207]

Thank you for your video and I agree an impedance inline can really help. It’s sage advice to over spec spec all magnetics!

[@davidc5027]

Thanks for the info Doug. 73 David

[@n4hnhradio]

You’re very welcome, David! 73, Doug

[@roundtracker]

Great video.. I was just told I had rf on my audio... I'd like to know what I sounded like so I can recognize what it sounds like..

[@n4hnhradio]

Your transmit audio will sound distorted. It could be slight or it could be horrendous. It’s not a bad idea to use a Mix-31 choke on the mic cable, but the source of the RF is often the shield of the coax, especially with an antenna that requires an antenna tuner. Snap-on, Mix-31, ferrites, like the ones in this video, are recommended. Make sure you get correct physical size for your coax.

[@ernietech-101]

Hi Doug, it's good to have videos about grounding in the shack. It's a topic that is more often overlooked, and certainly shouldn't be. My only add would be to remind everyone that you can't have too many good clamp-on ferrite chokes. Put them on the coax at the rig and at the antenna. And because RF runs on the outside of a conductor, put them on the DC and AC power lines as well.

[@n4hnhradio]

Yes indeed! That’s why I say the more the merrier. By choking the RF that is riding the shield of the coax into the shack, it should generally keep it from getting into the power wires. But sometimes you get RF from the antenna itself, if you are in close proximity to a radiating element. I have a friend whose antenna is right outside the house, at the same level as his radio and only 10 or 15 feet away. He gets RF from the antenna itself. He has snap-on chokes everywhere. It is a temporary setup though. He will be moving the shack to the basement as soon as his daughter moves out. She is living there while her house is being built. 73, de N4HNH

[@n4hnhradio]

You don’t seem to understand multiband dipoles (OCF, EFHW) or doublets very well. Common mode current is common when operating an antenna on a non-resonant band. The antenna match (aka antenna tuner) will make the transceiver or amp see 50 Ohms, but there are still standing waves on the feedline. Why have an antenna system that allows common mode current? Why not have a perfectly tuned antenna for every band? Many people live in a subdivision on 1/3 to 1/2 acre of land. They don’t have enough property to install a perfectly tuned antenna for every band, and keep them 1/2 wavelength away from their house and away from one another (look up proximity effect). You probably have a separate coax-fed dipole for every band. Not everyone has that much real estate to work with. Some don’t have enough land to install their antenna more than 1/2 wavelength away from their shack either. Radiated energy from the antenna itself can enter the shack. If you are fortunate enough to have a perfectly matched antenna for every band, with all of them installed more than 1/2 wavelength away from your radio shack, consider yourself blessed.

[@glennstevenson6242]

I learnt a lot from this video. Thank you.

[@n4hnhradio]

I'm glad you found the video helpful, Glenn. RF can be troublesome, but it is par for the course with certain antennas. However, for certain antennas, it can be worth the trouble. 73, Doug

[@xjohn1970]

I use them. I have 4 MIX 31's on my LMR 400 inside shack right after it leaves the FT-DX10

[@n4hnhradio]

They are very effective aren’t they?

[@Frank_K4FMH]

Good video, Doug. Miss Mark @ HRO! Consider a W1IHY Julius Jones iPlus switcher box for your rigs. Love mine!

[@n4hnhradio]

Hi Frank! I miss Mark too. I started buying from him in 1991. He had only been there a few years back then. 73, Doug

[@allenpamscofield]

I had a problem a couple of years ago with RF getting in the shack. When I keyed up, the display on my weather station scrambled. I put a small ferrite choke on the weather station power cable and that helped straighten up the issue. Later, I picked up one of the MJF-915 line isolators to try to keep RF out of everything else. I haven't had any problems since. Thoughts on the line isolators? I'm using an OCF and RG8X coax.

[@n4hnhradio]

Line isolators can be very helpful. With multi-band antennas, operating on a non-harmonically-related band, common-mode current can ride the shield of the coax back toward the shack. The antenna matching unit will make the transmitter happy but the standing waves still exist on the coax.

[@reidlanham2011]

Thanks for the video! On grounding, what is your recommendation for grounding a 2nd floor shack? The good news is that my shack is directly above the house ground rod, and I do have both a window and a pass thru to get outside. Thanks! 73, K8JLW

[@n4hnhradio]

When your shack is on the upper floor, you just have to run a longer ground wire. I know people who don’t run a ground wire. Their theory is that if you must run too long of a ground wire it can actually make matters worse. Mine is probably 25 feet to the ground rod, but so far, after 24 years I haven’t had an issue related to grounding. Since you have a direct route to make it to the ground rod, I would recommend grounding. 73, de N4HNH

[@reidlanham2011]

@@n4hnhradio Thanks! I had heard that too about too long of a ground wire but I will give it a go.

[@Frank_K4FMH]

Reid & Doug, I have a 2nd floor shack. I modeled mine after W8JI’s barn loft contest station. Before carpet was laid during construction, I ran copper tape strips in a 1’ grid pattern on the si flooring. They were soldered at each intersection. A 3” wide copper strap from GA Mtn Copper intersected the grid at my operating position. This strap continued into and down a pvc pipe installed behind the sheet rock and outside the brick (looking like a standard drain pipe) into a downward-facing elbow. The elbow has a cap with a slot for the copper strap which connects to the first of three ground ride run in sequence. They are close to a sprinkler head for some hydrangeas so the ground stays moist most of the year. With the advantage of new construction or just good luck in general, I’ve never had one indicator of RF issues my shack. I checked my ground bus against the ground strap going outside using an MFJ 931 without any appreciable need for adjustment on 160-10M. Someday you don’t need a ground reference in a 2nd floor. But I took this precaution while building. Thanks for your video, Doug, and your Q, Reid. 73, K4FMH

[@shawnp6653]

@@n4hnhradio Geez, some practical real world experience advice - thanks for that! Do you have just one ground rod outside a window -- that's what I would have to do (along with a fairly long wire from a buss bar to the window pass-though - probably use insulated stranded). 73 de KI5GX

[@n4hnhradio]

Yes Shawn. The rule books says keep the ground wire as short as possible but I needed enough to make it outside to the ground rod. It is hammered into the ground next to a deck support post, outside the shack. Inside, all the grounds from the equipment are connected to a common lug. 73, Doug

[@marks2254]

Hi Doug, Does the common mode current flow down the coax to the point that the ferrite is placed then get stopped there? If so, why not mount the ferrite on the coax outdoors before it enters the shack? Thanks. Mark

[@charlieoscar09]

That is where it should be.....Any returned RF into the shack is bad

[@n4hnhradio]

Great question, Mark! In the case of my Doublet antenna system, there is no coax outside. The ladder line comes in through the top of the window and immediately connects to the 4:1 BalUn. The common mode current is flowing on that 9 foot long piece of LMR-400 coaxial cable. For my other antennas, I have chokes outside as well. The coax going to the OCF dipole is coiled under the deck (2 turns at approximately 16-18” diameter) and I have chokes clipped over the 4 quadrants of that coil of coax. It did the same for the ZS6BKW. I coiled the excess coax and choked it. I’m fairly sure I showed that in one of the antenna work videos I shot this year, but I can’t remember which one. If snap-on chokes are enough, I prefer them. If they aren’t enough, I go to a 1:1 choke BalUn, outside if practical. The loss through a BalUn is minimal but if the snap-on is enough, there is no need for the choke BalUn. 73, Doug

[@marks2254]

I think I have Common mode current on my coax because my nearby tv turns on and off when I key the mic and my swr meter moved a lot when I touched the coax or the meter. In an attempt to fix that I put ferrites on the coax feed line. Ended up with 4 of them in the entry panel outside. That caused my low SWR point to move From 7.2 MHz to 6.6 MHZ and I couldn’t get it back to 7.2 by altering the antenna length. In fact, I couldn’t get it to move much off of 6.6 MHz no matter how much I changed the length. The ferrites did cure those two problems though. The next thing was to remove the ferrites, which restored my swr meter flinch and my tv problems. At that point I called my regular radio store and they recommend a coax noise filter from Palomar Engineers that is supposed to mount on the antenna connection of the radio then the feed line connects to the other end of the filter. The unit was too bulky to mount directly to the radio so they had me stand it off from the radio with an 18 inch piece of coax. That fixed the swr meter flinch but not the tv problem. When I asked why not choke it outside, they said I didn’t want to do that. I don’t know why. The antenna is an ocfd with a 4:1 unun at the feed point and it’s trimmed for 7.2 MHz. The mast is mounted to the house with one leg of the antenna passing within 10 feet of the radio room. Since ferrites fixed the problems it doesn’t seem like it’s an antenna proximity problem? The tv problem only occurs when transmitting at over about 50 watts. Any idea why the ferrites caused the low swr point to move and not be adjustable? Or why the radio store suggested the indoor filter instead of an outdoor choke? Any other comments or suggestions? Don’t worry too much about saving me money, I’ve ordered one of those 500 watt power combos from Elecraft so since the unun is only rated at 200 watts and the wire is only 18 gauge, that’s all going to be replaced anyway. The filter is rated at 500 watts but I’m guessing you’d say to upgrade it too?Thanks Doug.

[@n4hnhradio]

I’ve told some hams before that antenna work can sometimes seem like witchcraft. Sometimes the antennas don’t play by all the rules. I’ve had chokes move the point of resonance but not as much as happened to you. Are your chokes a Mix-31 type? Mix-31 works best for 10 MHz or less. But Mix-31 is also effective for up to 300 MHz. Mix-43 is good for 2-meters, and Mix-61 for 70 centimeters. I use Mix-31 because my RF in the shack problems fall well within the HF spectrum. With antennas from the doublet family, the length of the ladder line matters. My doublet is resonant at 17m because it was resonant at 16 MHz and I trimmed the ladder line to shift it. When it was resonant at 16 MHz, it exhibited a less than 2:1 SWR on 20m and 17m, but neither band was perfect. I needed less ladder line anyway, so I trimmed the ladder line and moved the resonance point to 18.130 MHz. If you watched the video where I tried the 97-Ohm 1:1 BalUn for my doublet, per the recommendation from BalUn Designs, the length of the coax between the BalUn and the amplifier/tuner shifted the SWR around. This is because the BalUn output impedance was 97-Ohms and the coax was 50-Ohms. The coax acts as a type of matching stub in that scenario. Now that I’m using a 4:1 BalUn (200-Ohms to 50-Ohms transformation) the length of the coax doesn’t affect the SWR. I proved that by trying 6 feet, 9 feet, and 12 feet of coax again. So, all that is to say, variables play into this. Coiling the coax can affect the SWR. How many coils can affect it. Could be good and could be bad. Ferrite chokes can change the match somewhat, though I haven’t personally seen it move as much as with yours. Anyway, I choke outside when possible, and inside. I like that Palomar Engineers sells the snap-on chokes in packs of 5, 10, or 15. These types of chokes are handy to keep around. 73, de N4HNH

[@marks2254]

Thanks Doug. Yes, mix 31. Witchcraft is the word I was looking for.

[@stevepatterson2290]

question what if you grounded your coax ( shield) on both ends ?

[@n4hnhradio]

Hi Steve! Well, RF ground and safety ground aren’t the same thing. And ground wires have to be kept extremely short or they too become radiators. Some ops will not ground anything. I know some. They’ve been operating for decades with no lightning damage. They swear by it. People with a shack on the upper floor would have to run a long wire to get to a ground rod. Then the ground wire itself could become the problem. The whole grounding thing is a can of worms. Me? I grounded everything. The chassis of the amplifier where that 9 foot piece of LMR-400 screws in is grounded to my ground rod. Maybe I should have tried it without the ground connection. But, the solution was simple. Snap-on chokes. People who can install a separate perfectly resonant antenna for each and every band probably don’t know what RF in the shack is. I have 1/3 acre. I had to borrow my neighbor’s tree for one side of my doublet. With a multi-band antenna, RF from common mode current is inevitable. 73, de N4HNH

[@stevepatterson2290]

@@n4hnhradio well I ground everything as well. everything goes to a ground rod I have a 6" shield ground to the same ground rod and at the antenna end another 6" shield ground. I use a hustler 5Btv 73s

[@n4hnhradio]

The 5BTV is a tried and true antenna. 73, de N4HNH

[@derletztezeuge1]

Does it matter where the ferrite chokes are placed on the coax ??

[@n4hnhradio]

I think it’s a good idea to place them nearer to where the coax enters the shack or just before it enters the shack. Just inside the shack can protect the ferrites from degradation due to sun and rain. But, in my case, the ferrites are working fine in the middle of the 9 ft. piece of coax. There is no coax outside for this Doublet. The ladder line comes in and connects to the 4:1 BalUn. The 9 feet of LMR-400 coax connects the BalUn to the amplifier/ATU combo.

[@spunkyspice4777]

I purchased to these cause my radio has this type noise while listening to the MW W band. These did not work. The instructions read to attach these to the radios power cord.

[@n4hnhradio]

These are to choke RF from radiating off the coax into microphones, computers, etc.

[@spunkyspice4777]

@@n4hnhradio I read several years ago these were for noise coming into regular listening type radios.

[@n4hnhradio]

They might help a little on RX but the voltage level induced on receive is nowhere near the voltage level on TX. I installed these to minimize RF radiating into my TX audio, which is the subject of the video.

[@spunkyspice4777]

@@n4hnhradio Is there any way to block noise coming in to the radio?

[@n4hnhradio]

@spunkyspice4777 yes. Some noise is atmospheric. You can’t stop it. The DNR in the Yaesu radios can help with atmospheric noise. Noise from power lines is best dealt with by using something like the Timewave ANC-4 or the QRM Eliminator. There is a playlist on my channel about dealing with noise. Noise from certain electronic devices in your own home, or a close neighbor’s home, has to be stopped at the source. Certain devices, like LED light bulbs, wall-wart power supplies, laptop power bricks, wireless phone chargers, plasma TVs, garden lights, food sealers, gaming consoles can be a source of noise. Power your radio with a battery. Turn off the circuit breakers in your panel one by one. Find out which circuit is producing the noise. Start unplugging devices on the circuit. You can find the exact device that is causing the noise.

[@kb9jqu]

Doug how did you verify the RF was gone? OTA testing to another operator or monitor function or something else? Thanks and 73 de kb9jqu - Curt.

[@n4hnhradio]

Curt, I listened through my Heil headset, using the monitor function. It was very obvious. Before the choke, I couldn’t run 400W on the 80-meter band. All other bands were fine. I only had RF in the audio when transmitting at 400W or more on 80 meters. Even with the choke, the RF started creeping back in at 700W. I added another snap-on choke and went to 1050W with no RF in the TX audio. I didn’t go above 1050W because my Elecraft software warned me. At 3.856 MHz I’m not supposed to exceed 1025W. That is the limit the Elecraft ATU calculated, based upon the SWR it had to match. I then tried it on the air. Jack, on 3.856, told me it sounded great. He was one of the ones who told me I had RF in my audio before. 73, Doug

[@kb9jqu]

@@n4hnhradio cool you could self test with monitor function. Good to know!!!

[@TheExtraTerrestrial]

Any tips about problems with speakers making noise? I have a pair of Audioengine A5s on my PC (which is in the same room), and whenever I tx, they make some sound.

[@n4hnhradio]

Speakers can be a touch one to deal with. Snap-on ferrite chokes or ferrite chokes that have a inner diameter to allow you to loop the speaker wire 2-3 times through it. I’m using a Bose computer speaker system with no issue. I was also getting into the 1991 era surround sound system for our TV. I replaced it with a VISIO sound bar and all is good there now. I hope this helps. 73, de N4HNH

[@TheExtraTerrestrial]

@@n4hnhradio Cool, I will give it a try. I have some snap-ons on hand. Which cord should I put them on? The left speaker plugs into AC and has it's built-in amp, and then it connects to the right speaker via speaker cable. They are connected to my PC with a 3.5mm plug. Is this just one of those 'try it and see' things? Worst case, I can just turn them off, but would be nice to sort out.

[@n4hnhradio]

Snap the ferrites on each and every wire that you can. 73, Doug

[@tomm899]

What does rf sounds like in the Audio?

[@n4hnhradio]

It sounds like a crackling distortion. It’s just plain nasty. Depending upon the amount getting into your audio, it can span from a minor crackle to bad enough that people can barely understand what is being said. Sometimes RF gets the blame for a poorly setup ALC. That can also create a type of distortion. I don’t use ALC for my amplifier. I just carefully set up my TX audio. 73, de N4HNH

[@tomm899]

@@n4hnhradio THANKS. K4VTE

[@Totalplonker]

Speaking about audio... I experienced RF interference in my home theatre setup and it was only after thorough investigation that I finally solved it by purchasing shielded cables. 🥳

[@n4hnhradio]

Shielding cables are great but they don’t stop all RF. RF loves a shield.

[@Tinman386wisconsin]

What did it sound like when you had rf in your audio? If i try to low drive my amp my audio sounds pinched and distorted. I'm now thinking that might be the problem. When i increase drive it cleans it up at least enough to see improvement but i don't like running max power all the time.

[@n4hnhradio]

Generally speaking, RF in your audio will be worse the more power you run. It’s makes your TX audio sounds distorted.

[@fairbanksmorse112hpheadles3]

You cannot get rid of rf from your shack! You are transmitting rf form your antenna and it permeates you and everything out to infinity.

[@n4hnhradio]

We walk around in electromagnetic radiation all the time. Not enough w/m to affect us, thankfully. Our antenna system, if installed correctly, will direct our signal away from us - most of it at least. The RF in this video is from common mode current. Read about commode mode current, as it relates to antenna systems. It comes in on the outermost portion of the shield of the coax.