Many hams find that their HF mobiles receive more noise than they do usable signals. Common noise sources include the ignition system and alternator.

Spark plug noise is propagated through ungrounded body panels and the exhaust system, which is normally suspended from rubber vibration dampers. The rubberized supports insulate the exhaust from ground, essentially creating a radiating spark antenna.

To deal with spark noise, use tinned copper braid to electrically connect the hood (or bonnet) to the firewall of the vehicle. This will turn your hood into a Faraday shield. Stainless steel clamps of the proper size may be used to clamp braid to the exhaust system, (typically in two places- one near the front and one in the rear) thereby reducing the radiation of noise. DX Engineering DXE-TCB-050 Tinned Copper Braid is a half-inch wide and ideal for this purpose.

Kenwood PG-3B Inline DC Noise Filters PG-3B

Kenwood PG-3B Inline DC Noise Filters PG-3B

For alternator noise, products like the Kenwood PG-3B Inline DC Noise Filter will eliminate noise from DC supply lines in radios up to 100 watts output. As a fringe benefit, noises other than alternator noise, like that of onboard system control computers, will also be reduced.

You really don’t have to suffer with vehicle-generated HF noise. A little elbow grease and some handy tools and parts will go a long way toward making HF mobile operation more enjoyable.

Hamvention 2016 officially began this morning! But before we get into that, we want to share what occurred during a very busy day yesterday.

If you followed along, you’ll know Content University 2016 was absolutely packed. After CTU wrapped up at the Crowne Plaza Hotel, Four Days in May began at the Holiday Inn in Fairborn, OH. There was also the Content Super Suite, and the ever-popular Contest Super Suite pizza and wing party.

In between it all, DX Engineering found time to set up its Hamvention booth, which will feature several new products this year.

But the highlight of the night might have been the ICOM dinner, which was Star Wars themed. And yes, that does mean Star Wars “characters” made an appearance. We have the exclusive pics below.

Stay tuned this weekend to DX Engineering’s Facebook, Twitter and Instagram accounts as we bring you more live coverage from Hamvention. And follow the DX Engineering blog throughout the weekend for behind-the-scenes coverage from the show!


Hamvention has not yet officially begun, but hundreds of Hams have herded themselves into Dayton already for Contest University 2016.

The event has been sold out for some time, and only standing room remained this morning in the Crowne Plaza Hotel ballroom in Dayton, OH, where things kicked off at 7am.

Last night’s activities included CTU registration, a live broadcast of Ham Nation, and a pizza party, which wrapped up around 11pm.

CTU 2016 professors include: Val Hotzfeld, NV9L; Doug Grant, K1DG; Frank Donovan, W3LPL; Ed Muns, W0YK; Rob Sherwood, NC0B; Joel Harrison, W5ZN; Tim Duffy, K3LR; Bob Wilson, N6TV; Tim Jellison, W3YQ; Greg Ordy, W8WWV; Kirk Pickering, K4RO; Andy Blank, N2NT; and H. Ward Silver, N0AX.

DX Engineering, a premier sponsor of Contest University, is on hand at the event and will provide social media coverage during Dayton Hamvention. Stay tuned for more info and coverage from Hamvention 2016, and take a look at our CTU registration and class pictures below:


RF lightning protectors are designed to protect RF equipment by equalizing the potential difference between the center pin of the coax cable and its shield. The majority of RF protectors do not feature indicator lights to show whether or not they are still functioning. Since power is not readily available at some installation points, an indicator light is not practical.

So how do we know if the protector is still functional?

PolyPhaser Coaxial Lightning Protectors IS-50NX-C0

PolyPhaser Coaxial Lightning Protector IS-50NX-C0

Since the IS-50 and IS-B50 are the most widely used PolyPhaser RF protector series, application in Land Mobile Radio, SCADA systems, amateur radio and many others, this paper focuses on their specific testing condition.

The following whitepaper from PolyPhaser includes an overview of how lightning protectors work and how to test for and assess possible damage from lightning.

See the PDF from PolyPhaser: Testing RF Lightning Protectors without Indicators.

Question: What’s an easy and inexpensive way of improving my mobile radio receiver performance?

Most mobile installations, for safety reasons, position the radio out of the way, under the dashboard, on the passenger side of the vehicle, or even under the seat! As result, the mobile radio speaker is often facing down, away, up at the dashboard, or into the carpet.

Yaesu FTM-3100R VHF FM Mobile Transceivers FTM-3100RSome radios, like the new series from Yaesu that includes the FTM-3100R and the FTM-3200DR, include a “front facing” speaker. This is an improvement, but it might be facing your passenger’s knees rather than your ears.

So, what do you do?

Answer: Use an external speaker, and mount it closer to your ears!

There are many options available, but DX Engineering has a very economical speaker that works great: the DXE-281. This will allow you to position the speaker closer to your ears and reduce the interference from road and other noise.

How and where do you mount it? There are as many ways as there are different vehicle styles and configurations. You may have to use your imagination. In this writer’s case, there is an unused sunglasses holder built into the headliner of the vehicle.

DXE-281 in Sunglasses Holder

This provided a perfect place to position the speaker much closer to the driver’s ear, and it required no drilling or other modification of the vehicle. This is but one example of a simple, inexpensive, but effective mobile installation upgrade, and it cost less than $20!

DXE-281 in Car Sunglasses Holder

Many hams ask why they should bother to add the recommended radial field to their ground-mounted vertical antenna. There are reasons why it’s a good idea.

Ground Radial
Ground-mounted verticals use the Earth as their counterpoise. The vertical radiator is only half of your resonant or non-resonant vertical antenna. The other half is counterpoise; an imaginary radiator directly opposite, and on axis with, the wire or aluminum standing on the ground. This second half essentially makes your antenna a vertical dipole. Because of varying soil conductivity and chemical composition, some “ground” is better at the conduction of RF energy than others.

Why does the ground need to conduct at all? The vertical does that. Consider that your antenna represents a load at the end of your coax. Ideally, the RF current flows out the center conductor from the transmitter, but also must flow back to the transceiver on the coaxial shield to complete the current loop. If the vertical is radiating the current, then where does the returning current flow come from? The answer is the ground!

A radial field enhances the ability of the ground around the vertical to conduct RF energy. The radials “collect” the return current required for efficient antenna operation. Some hams complain that radials narrow the bandwidth of the antenna. This occurs because the radial system raises the “Q” of the antenna system. The higher the “Q” value, the more efficient the antenna will be. With a good radial field, radiation resistance will decrease, RF current will increase and bandwidth will narrow. That is just as it should be. Be aware that a poorly efficient antenna can have a good SWR. How efficient a radiator is a 50 ohm resistor across your coax? That’s called a dummy load and they all have very low SWR!

When your vertical is ground-mounted, use a good radial field to raise radiation efficiency. You’ll have a better antenna system that will benefit your station and the joy of your radio hobby.

Question: Is it OK to run an amplifier on 120 volts AC?

This is a question that many new Amateurs ask themselves when they’re buying their first amplifier. There are many reasons to ponder this, and one of them is: “I’ve already got a 120 volt outlet in the shack, and I don’t want to spend a fortune putting in a 240 volt line.  Electricians are expensive!”

“What difference could it make? I’m going to be running about a kilowatt output regardless of the line voltage. I know that a typical 1 kW output amplifier will draw a maximum of about 15 amps on 120 Vac and 7.5 amps on 240 Vac. In either case, that’s about 1,800 watts input (120V x 15A or 240V x 7.5A) and since Ohm’s law tells us that volts x amps = watts, there should be no difference – right?”

Wrong! That ignores voltage drop.

There are many reasons why running your amplifier on 240 Vac is a lot better:

  • Line voltage regulation is better.
    1. Typical voltage drop of drawing 15A on a 120 Vac 20 Ampere circuit (12 gauge wire) is about 3 percent. This means that every time you transmit, your 120 Vac line is going to sag to about 116 volts.
    2. This doesn’t seem like much of a difference, but in a tube amplifier, your high voltage is going to also be sagging by that same 3 percent! If your amplifier uses 3,000 Vdc, it will be dropping 3 percent to about 2900 Vdc (and all your other power supply voltages will drop by 3 percent, too!)
    3. This will cause the line voltage that your other appliances receive to drop whenever you transmit. This is enough to cause noticeable dimming or blinking of typical household lighting. This doesn’t go over well with spouses and kids!
  • On a 240 Vac 20 amp circuit, you will draw half as much current.
    1. By the above analysis, you’d think that this would result in your 240 line voltage dropping by only half as much as we saw on 120, or 1.5% – but, you’d be wrong.
    2. The benefit of twice the line voltage results in a whopping 4:1 improvement in line voltage regulation and your 240 volt line will only vary by 0.75% to 238.2 Vac when you transmit. Even on a 240 Vac 15 amp circuit (with smaller 14 gauge wire) you’d only have a 1.2% drop to 237.12 Vac.
    3. On 240 volts, your high voltage will only vary 0.75% instead of 3 percent. That 3,000 Vdc will only drop 22.5 Vdc when you transmit to 2977.5 Vdc – way better than dropping to 2900 Vdc! All of the other power supply voltages will remain more stable and only vary by 0.75%!

You’re making a significant investment in your amplifier. Give it the 240 Vac power it deserves so it can give you the best performance!


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