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The best sources for RFI/EMI in the shack are Grounding and Bonding for the Radio Amateur by Ward Silver, N0AX, available from ARRL, and K9YC.com, Jim Brown’s web site.
Bonding is NOT grounding, but critical for safety and surge protection. Using ferrites properly helps to keep RFI out of the shack. If you operate HF, both concepts are critical to your success!
73, Bill, K8TE
Be careful when using a switch arrangement which has two radios sourcing one or more antennas. The isolation rating of the switch is very important in such cases because RF during transmit on one radio is physically very close to the receive input of another radio. Depending on power levels the receive front end could be overloaded and burn out. Check the isolation specifications of the switch and highest power output you are planning.
73 Dave K1KA
Hi James,
probably not going to hear us. I’m one of the net control stations. I use a dipole and 100w only.
ab1oc the other NCS has legal limit with beam antennas, but he typically doesn’t use that for net control ops, so to reach a broader audience. If Fred switches to the beam and rubs power, it is much more likely you’ll hear Fred.
sorry, but 10 has been a tough band the past several years for DX.
Hi Luke,
I’d like to provide some experience on mobile VHF work. I’ve been running VHF/UHF mobile since 1994, and I no longer use anything other than permanent mounts. I’ve found the absolute best mount possible is an NMO mount. These have the absolute best connection to the truck body, both electrically, mechanically, and RF-wise. My commute is 75 miles each way, and I can hold the repeaters I use for almost the entire trip. For the pickup truck V/U rig I run a dual band FTM-100 FM rig (this includes fusion C4FM.)
I buy my vehicles, run them at least 200,000 miles, and don’t give two craps about worrying about a 3/4″ hole “affecting resale.” My last commuter vehicle ran 250,000 miles (a mazda 3) and I enjoyed excellent ham radio operation for the entire period of ownership. Toss a $3 cap on the antenna mount, and the wholesaler will think it’s a GPS antenna when they drag it to the auction.
For installation, I pop the dome light out of the interior, and drill through the roof with a pilot hole.
Then, from the outside, I’ll use a step-bit drill to cut a super clean hole to install the NMO mount.
My preferred antenna is the Larsen NMO 2/70: https://www.hamradio.com/detail.cfm?pid=H0-000566
the coax is then run over the headliner, and down the B pillar. This way you don’t have any gasket issues.
As for 6 meters, I run a second radio. my second radio is my 6m-160 FT-891. The antenna that I am using is the Hustler mono-bander. I have that mounted to a custom rack over the bed of the truck. This is a full size pickup, so there is plenty of room for a second radio – you just need to figure out the mount. I found a base from Havvis that mounts to the center console seat bolts. here is the link to the seat mount: https://www.havis.com/products/SUB_BRKT_HUMP_1PC_SILV_14_20_TAH_15_20-122310-963.html
I’m still working out the details on the HF installation – these things take time, and you need to try something to see if you like it.
The 891 also has FM, and I’ve been finding quite a bit of phone FM activity on 6 meters! the other really cool thing about 6 FM through repeaters… dare I say you get almost 100 mile coverage.
I think 6m FM is something we should do more of, and of course it is vertically polarized.
There are plenty of options out there. I hope Fred’s and my suggestions help you sort out how you want to go. Have fun out there!
Will today’s “shopping trip” be recorded and available at another time for members, as you did for last week’s Bootcamp?Thanks.-Mike, N3JNH<p style=”text-align: left;”>Thanks Fred. I expect mostly FM repeaters while driving to/from central NY periodically. I’m looking at this as an opportunity to potentially work with 6M, but is it practical while driving?</p>
Ladder line needs to have clearance from conductors for 3 to 5 “widths” around it, or more. Otherwise you run the risk of coupling energy to the outside conductor. At HF frequencies, ladder line is a great choice, but getting it into the shack must be done with care.
As others have pointed out, a 1:1 balun is a good transition from ladder line to coax. Its common-mode impedance should be about ten times the characteristic impedance of the coax. More is better, but do not allow the windings to become self-resonant. (See _Transmission Line Transformers_ by Sevick for a detailed treatment.) #61 material or K-type material is appropriate at HF. Possibly #43.
The use of the tuner means that none of the transmission lines are “flat”, there are mismatches, especially if you are using a fixed doublet antenna (i.e. a dipole but not really half-wave) over many bands. Here, the important thing is getting from a balance line to unbalanced line (coax) to get into your tuner for an impedance transformation to 50 ohms.
The jumper wire shown in the manual between J105 and J106 is the conductor of all your transmitter current, and is no place for a ferrite bead of any kind. Killing the patient is not the same as curing the disease. But, I think you already figured that out.
The “balun” T101 in the schematic is a bit of hack, and is inferior to a 1:1 choke balun. It is more properly called an autotransformer. A major difference is that in normal operation the core of T101 is seeing all the flux from the currents due to the transmitter power. In a 1:1 choke balun, a true Transmission Line Transformer, the core only sees the “error” current, thus little or no flux, and therefore the core’s losses contribute little loss to the system.
The advice to abandon the internal “balun” T101 (“A” in photo) is good advice. And if, where you locate the external 1:1 choke balun (“B” in photo), you ground the coax before it enters the shack, you should greatly reduce local RF currents which may be causing your RFI/EMI issues.
Respectfully,
Spencer, W2SW
Tom,
You don’t mention what antenna the feedline connects. Just because you have 450 Ohm ladder line doesn’t mean the impedance at the bottom end is 450 Ohms, much less without reactance. It’s possible it is much less. It is a common misconception one should always use a 4:1 or 9:1 BALUN with ladder line. The appropriate BALUN value is much more complicated than that. A 1:1 BALUN may be a better choice.
The advice to use a toroid common mode choke is on the money. However, the best place to use it is first at the transition from ladder line to coax. Jim, W8JI, an well-known and respected authority on antennas and transmission lines has an article on the G5RV which I am guessing may be your antenna at: https://www.w8ji.com/g5rv_facts.htm. An excellent, and probably the best, source of information on using ferrites is K9YC.com. Like W8JI, Jim uses modeling and scientific measurements to make his points, rather than anecdotes and Amateur Radio lore.
73, Bill, K8TE
Hello Tom,
I am not sure if you have solved your RF monitor issue or the balun heating issue yet. For the monitor, I would recommend supplementing additional ferrite chokes on the HDMI or USB cable.
On the choke heating. If I am correct in understanding your description and after reviewing the document provided, the choke installed on the jumper wire will heat up due to seeing full common-mode RF current on this single wire. With the switch in position 6, your RF current is traveling on the jumper wire to the interior balun connected to your feed line. Without opposing “differential mode” current the choke is attempting to impede your full RF current and quickly becomes saturated generating heat. I would suggest reviewing alternative mitigation options for the original problem.
Regards,
KC1MDHScott
Hi Tom,
A good balun will certainly work as Fred suggested. But to speak to the excess heat being generated… snap-On ferrites are much less efficient than the Torroid style ferrite chokes.
I would replace that Snap-On #31 ferrite with a #31 Torroid Ferrite, and put about nine turns of Rg8X through the ferrite core. for a great source of torroid cores try this link to Palomar engineers: https://palomar-engineers.com/antenna-products/1-1-balun-kits
Snap ons will work, but in order to stop excess heat, you need quite a long “train” of them.