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Author Topic: Antenna Question  (Read 1569 times)
K3CLT
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Posts: 59




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« on: December 04, 2006, 01:44:36 PM »

Are some HF whip antennas more noisy than others?
I have the Yaesu 857d installed in a 2005 F-150 pick up truck.
I am using Iron Horse antennas for the different bands, all except 20 which is a Hamstick.
With the engine off I run a noise level around S-8 all the time. When I start the truck it goes up one S unit.
I took the antenna off the truck while it was running and the noise went away. I was parked with the engine off and another truck came by and I heard his ignition noise in the radio.
I want to investigate the noise in the truck but want to get a handle on the external noise if I can. It won't do much good to eliminate one if I can't get the other under control.
I was just wondering if the noise level has to do with the gain of the antenna.
I work around Central NJ and some areas the noise level is around a +15.
I am open to any reasonable suggestions. Remember what your ma told ya. If you don't have anything good to say then go back to 11 meters...
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AA4PB
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Posts: 15067




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« Reply #1 on: December 04, 2006, 02:05:08 PM »

In general, the better the antenna receives signals the better it receives noise. With mobile whips, the more loss the antenna has the less noise it picks up BUT it also picks up less signal.

If you are driving around town picking up external noise from power lines, computers in stores, etc. there is not much you can do about it except to drive to a quieter location. A good noise blanker in the receiver can help with pulse type ignition noise (pop, pop, pop) but usually doesn't do much for other types of noise.
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Bob  AA4PB
Garrisonville, VA
K0BG
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Posts: 10248


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« Reply #2 on: December 04, 2006, 03:57:38 PM »

You can garner a lot information by visiting my web site. That said, if you haven't bonded the bed, and other chassis points, you're going to have a LOT of noise.

RFI from ignition, fuel injectors, fans, IAC motors, and a host of other devices do add insult to injury. Most, can be curbed enough to make mobile operation tolerable.

Antenna mounting location and method are also important. Mag mounts, bumper mounts, or any temporary schemes are all suspect. Good wiring is also important.

Alan, KØBG
www.k0bg.com
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K3CLT
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Posts: 59




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« Reply #3 on: December 04, 2006, 04:07:20 PM »

I have the antenna mounted on a mount on the side of the toolbox in the bed. I have a braided ground running from the mount to the bed. I have another running from the mount to the frame. I have one from the bed to the frame. I have one from the radio mounting bracket to the frame.
I have one from the exhaust to the frame.
I have a place on the inside of the bed where I can mount an "L" bracket but I was not sure of that location because it would put the antenna closer to the back of the cab.
I have to watch where I mount the antenna because this is a work truck and from time to time one of my guys may have to load something in the bed and may not be as careful as I am.
I have read your posts on this site and was going to make  a short antenna to start looking for some hot spots in the truck.
Right now I think the truck has about one S unit more noise than the area I'm working in but I did want to get some feedback from some of the hams here before I started going after the noise.
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N5EAT
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Posts: 175




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« Reply #4 on: December 05, 2006, 11:28:51 PM »

All of the mobile rigs I have are equiped with digital signal processing.  This helps a lot.  I have been lucky with my current automobiles (mustang, z-28, and Mazdaspeed Protege).  None of these cars produces a bothersome hash in my radios.  However, on the interstate or in town - I do get lots of hash from other automobiles (where the DSP comes into play).

Unlike Alan - I've used a magnet mount very successfully on my vehicles.  I do have them attached
to the car by more than their magnets as I don't want the antenna and mount to come off and ruin some innocent party's life.  

The last 5 or 6 years, I've not wired radios directly to the car's battery.  This is a great place for the electrical wiring to pick up lots of engine device noise.  The accessory plugs work well for my applications.  I don't have a problem with them heating up, etc; and these connections are quieter than a direct wiring to the battery.  However, A battery in the trunk to which is attached a trickle charger should be nice and quiet(if the battery's only use is to power your radio).  You might want to experiment with a seperate battery for your rig.
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K0BG
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« Reply #5 on: December 06, 2006, 12:24:39 PM »

Mark, lets not start folks out on the wrong foot.

Connecting direct to the battery DOES NOT increase any type of RFI, EMI, or ADI. In fact, it has been shown many times that the opposite is true. In fact, the big three all suggested direct battery connections.

The problem with accessory sockets is the size of wire feeding them. Most of the time it is 16, and in a few cases 14. Even size 12 is inadequate for a 100 watt output radio. While you might not have any problems (yet), using them is a prescription for all things bad.

Adding insult, MFJ has come out with a device which contains a Farad cap, charging circuit, and other goodies to "allow the use of an accessory socket" with a 100 watt radio. It is, nonetheless, a poor idea.

With respect to mag mounts, no matter how many magnets they have, they add ground loss to a system that has too much ground loss as it is. But that is not the reason I don't recommend them. The bigger and heavier they are, the more likely they are dislodge in a crash. Adding insult, most insurance companies will not cover losses for devices not permanently attached to the vehicle in question.

If we're going to recommend alternative hookups, at least lets make sure we give both sides of the story.

Alan, KØBG
www.k0bg.com
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AA4PB
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Posts: 15067




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« Reply #6 on: December 07, 2006, 05:07:12 AM »

I agree with Alan here. It would be a poor radio that permitted engine noises picked up by a power cable passing thru the engine compartment to enter the radio. Other than alternator whine (which is really an audio frequency noise), most noise enters via the antenna. It is simple to verify this by disconnecting the antenna at the radio.

Lighter socket wiring is not sufficient to support a 100W radio. In addition, there is no reason to believe that wiring to a lighter socket would pass any less noise than direct wiring, in fact the opposite is true.

Virtually every commercial radio installer wires directly to the battery or to a nearby connection if it is provided.
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Bob  AA4PB
Garrisonville, VA
AD5X
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Posts: 1626




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« Reply #7 on: December 07, 2006, 07:05:41 AM »

“Adding insult, MFJ has come out with a device which contains a Farad cap, charging circuit, and other goodies to "allow the use of an accessory socket" with a 100 watt radio. It is, nonetheless, a poor idea.”

Actually, the MFJ-4403 looks kind of intriguing to me.  In my early mobile days, I used a 12V 4-AH battery plugged in parallel with my cigarette lighter socket to power my TS-50 (my mobile radio at the time) which easily handled the SSB peak current required.  Worked great, though it was definitely a kludge!   Recently I bought a Gamma HPS-1a power supply that consists of a tiny 12V 5-amp switching power supply with a 5-farad capacitor bank at the output (see my review at www.ad5x.com).  This power supply does a great job of powering my IC-706G at 100 watts SSB.  The capacitor bank provides the peak output current, and the small switcher re-charges the capacitors in between the peak current demands.  According to their ad, the MFJ-4403 has a 4-farad capacitor bank.  It seems that this should work pretty well with the 10-15 amp cigarette lighter capability.  Not that I need this (my cars have DC power cables wired directly to the battery or to alternate high current accessory connectors), but I’m going to get one when they are available and play around with it.  I’ll put a review here on eHam after I’ve evaluated it.

Phil – AD5X
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N5EAT
Member

Posts: 175




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« Reply #8 on: December 13, 2006, 08:21:14 AM »

Alan:  I was noting that you don't like the idea of mag mounts.  Anyone who reads your website (which I have several times) would know that.  I was just mentioning that I have had really good luck using a mag mounting with HF.  I have also had some dedicated
mounts with actual holes drilled into the roof of my car.  

I have found a good mag mount on the roof of a car to work pretty much as good as a drilled-in mount.  I've found it to work better than many bumper mount situations (which you've mentioned).  I may not have phrased my reference to you properly.  I hope you did not take offense.  I consider you to be the authority on mobile hamming on EHAM.  I mentioned your dislike of mag mounts so as to direct the reader to take your advice in preference to my own.  In other words, a compliment. You are correct that a mag mount can prove dangerous to others.  I tend to anchor my mag mounts via drilling holes in the roof rain gutters(etc) and
attaching guying for my antenna system should it be knocked loose.  

My personal experience is that when I've run wiring directly to the car battery under the hood, the extra length of wire tends to pick up more engine generated noise than the short wire I use with the accessory plug.  Also, on 10 meters - you can really get RF back into the radio via the power cord as the cord gets longer.

For what it's worth, if you took offense at the manner in which I used you as a reference, I apologize as I did not mean it as an indication that you, the expert, would highly disagree with me.  I actually consider you a beacon of intelligence in these forums.
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W0FM
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Posts: 2080




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« Reply #9 on: January 04, 2007, 02:40:19 PM »

N5EAT states:

"My personal experience is that when I've run wiring directly to the car battery under the hood, the extra length of wire tends to pick up more engine generated noise than the short wire I use with the accessory plug. Also, on 10 meters - you can really get RF back into the radio via the power cord as the cord gets longer."

I personally think the opposite is true.  There is still wire running from the accessory power socket that, eventually (if not directly) runs all the way up to the battery.  It may consist of multiple lengths of varied gauge, but it's still has to get from the socket to the battery.  Add to that the cord from the accessory power plug up to the back of your rig (usually another 3-6 feet) and I think the combination actually equals more linear feet of wire than would a direct connection to the battery terminal.

Just an observation.

73,

Terry, WØFM

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