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Author Topic: Best band for testing when adding grounding to car?  (Read 3371 times)
G7MRV
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« on: February 20, 2013, 07:34:27 AM »

Ok, so after months (probably years) of talking and planning, I am finally in a position to start adding the ground straps to my car.

I understand that as I increase the grounding, the resonant frequencies of my antennas will change, due to the feed impedance changing (lowering I hope!), So I plan on measuring the system before starting, and then again with each additional strap, to keep a track on the changes.

But, I don't want to be changing the antennas all the time, so what would be the band best suited to testing this on? In other words, which band will I see the biggest changes per additional ground strap?

My instinct is taking me two ways! On the one hand, a high band like 10m is more sensitive to changes in length of antenna system components, but a low band, say 40m, is much more dependent on the quality of the grounding.

Testing of the system will be done using an MFJ-259 analyzer and my FT-857.

Martin
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K5LXP
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« Reply #1 on: February 20, 2013, 08:08:35 AM »

This doesn't make sense.  You're not going to "adjust" your bonding to suit a particular antenna.  Not sure what you mean by "changing the antennas all the time".  Once you've tuned one for a particular installation, it's not going to (or, at least shouldn't) change.

Bond every panel, every door, the engine, driveline and exhaust.  When you're done, *then* tune your antennas. If the tuning point shifts radically all you've demonstrated is how poorly bonded it was before.  Measuring the effect of every strap for every antenna sounds like a very tedious and ultimately irrelevant effort.


Mark K5LXP
Albuquerque, NM

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KB4QAA
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« Reply #2 on: February 20, 2013, 08:13:59 AM »

Are you wanting to do measurements out of curiosity?  Or are you planning to only do a minimum of bonding...just enough to improve one or more bands a sufficient amount?

Unless you have a truly atrocious antenna installation I don't think you are going to see dramatic shifts.   You will generally see the impedance come down a bit, and see more consistent broader swr curves.  The gravy is that reception will improve and noise level decrease.

I plan for a basic installation to be:  1 strap per door, two straps per hood/trunk/bonnet/boot, 1 on tail pipe

Do the basic install, then you can step back, measure and admire the improvements.  You can then explore additional bonding, such as more exhaust system strapping, second door straps, and finding any particular offending systems.

Alan K0BG has an excellent discussions and examples:  www.k0bg.com



« Last Edit: February 20, 2013, 08:16:03 AM by KB4QAA » Logged
G7MRV
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« Reply #3 on: February 20, 2013, 08:20:44 AM »

Mark,

It makes perfect sense. Each new strap will change the performance of the system, and I will be measuring the systems parameters after each strap is added. I am not adjusting any of the antennas, only observing the change in the system. What I wish to know is which band will give me the most observable change.

There is very sound reasoning for testing after each step - I cannot have the vehicle off the road to do them all at once. Therefore, any number of things could go wrong. By knowing the system parameters at each point, If I am forced to rapidly make good I am able to retest and ensure all is well before adding the next strap, which may by days or weeks later. It also means I can detect if I foul something up.

What I meant by changing the antennas, is not changing the lengths etc of the antenna, but swapping the antennas between the high band and low band ones. I use separate antennas for each band I operate on. By selecting the best band to observe the effects on, I always have the system set-up the same each time I work on the grounding.

There is also an educational aspect. I want to see how each new bond affects the system, and to learn what the magnitude of those changes are for each different area of the vehicle being bonded.

Martin
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G7MRV
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« Reply #4 on: February 20, 2013, 08:23:29 AM »

Are you wanting to do measurements out of curiosity?  Or are you planning to only do a minimum of bonding...just enough to improve one or more bands a sufficient amount?



Alan K0BG has an excellent discussions and examples:  www.k0bg.com



Yes, partly. I want to observe the way the changes affect the system. But also to check with each step that nothing has gone amiss. Its likely each step may be some time apart. By checking with each step I also ensure Ive not done something silly like one end of a strap isnt making sufficient contact.
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AA4PB
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« Reply #5 on: February 20, 2013, 08:45:11 AM »

Grounding/Bonding is going to have the geatest affect at the lower frequencies. Anything that reduces losses at the lower frequencies will also help the higher frequencies to some extend. I'd do the testing/measurements at the lowest frequency.
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G7MRV
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« Reply #6 on: February 20, 2013, 08:59:29 AM »

Grounding/Bonding is going to have the geatest affect at the lower frequencies. Anything that reduces losses at the lower frequencies will also help the higher frequencies to some extend. I'd do the testing/measurements at the lowest frequency.


Thankyou, thats confirmed what I was thinking.

The lowest I can use is 40m, which is the lowest thats practical for me mobile, so I will use 40m

Cheers

Martin
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N6AJR
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« Reply #7 on: February 20, 2013, 09:14:44 AM »

I use a braid fro the battery to the fender  near by.  I use a ground fro the radio to the chassis ( usually  a self tapping sheet metal screw driven through the floor boards) and then aI run a strap from the antenna mount ( shield side) to a point on the chassis of the car,    this is a goiod start and will probably be enough. do more if you feel like it.  have fun, enjoy
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M6GOM
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« Reply #8 on: February 20, 2013, 06:50:34 PM »

I use a braid fro the battery to the fender  near by.  I use a ground fro the radio to the chassis ( usually  a self tapping sheet metal screw driven through the floor boards) and then aI run a strap from the antenna mount ( shield side) to a point on the chassis of the car,    this is a goiod start and will probably be enough. do more if you feel like it.  have fun, enjoy

No it isn't a good start as it creates ground loops.....

Martin...

Just use flattened RG213 braid and go across the hinges on the boot/hatch and again on the bonnet although I found doing just one hinge on each gave the same reading as doing both sides but still did both sides as a "belt and braces" method. You can do the doors but I noticed no observable difference on my Mondeo with the analyser. I also didn't notice any difference bonding the exhaust to the car either but if you get RFI it is worth doing that.

Don't bother using the FT857 to do this - just use the MFJ and observe the frequency that x=0 is at and what R reads after you've added a strap. By the time I'd stopped adding bonding, the resonant frequency of my Tarheel had dropped over 300kHz.

« Last Edit: February 20, 2013, 06:56:42 PM by M6GOM » Logged
K1CJS
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« Reply #9 on: February 21, 2013, 04:18:10 AM »

The greatest change in resonance or giving your antenna a "ground plane" to work against will be when you bond the hood and trunk lids, to a lesser extent, the doors.  The bonding of the engine and the various other metal components of the car is done to lower the noise the rig receives--and possibly transmits--as much as possible.

Multiple ground points in the rig power supply leads will create ground loops, especially when you start bonding the various car components together.  That is one reason that most hams will take the factory recommendation and run the power leads back to the battery, making the power connections there, near the battery.  I'm not going to re-ignite the old argument about connecting to the battery terminals here.
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W8JX
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« Reply #10 on: February 21, 2013, 08:18:52 AM »

Grounding/Bonding is going to have the geatest affect at the lower frequencies. Anything that reduces losses at the lower frequencies will also help the higher frequencies to some extend. I'd do the testing/measurements at the lowest frequency.


I disagree, it has been my experience improper or inadequate grounding/bonding will effect higher HF bands most in a mobile. Especially when dealing with ground looping and RF feed back.   
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N6AJR
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« Reply #11 on: February 21, 2013, 10:03:49 AM »

M6GOM, I beg to differ with you.  In my car I have a trunk lip mount on the trunk lid and when driving at speed the trunk lid floats up and down on the rubber gasket and the hinges make intermittent contact, causing picket fencing while driving freeway speeds..With a ground from the battery to the chassis, and a ground fro the radio to the chassis, and a ground braid from the shield side of the mount to the bolt on the chassis side of the trunk mount solved the problem.  no ground loops, every thing has a ground to the chassis, and it is a unibody construction car.

In my pick up I have five radios , several of which are multiband and have 8 antennas. 4 are on the roof of the cab ( 220mhz/900 mhz/1.2 ghz and a 2m 440 ) on nmo mounts and the other 4 are on the bed rails, ( 2m/440/6m , a 2m only, an ATAS 120 and a DK 3, mostly for 80 and 160 mobile).the truck has a grounded rack holding the radios, and the coax shield for all the antennas is grounded at the antennas, and there is bonding between the battery and the chassis. They all work fine with no problems.

I also have a 1600/800 watt poser inverter for 120 volts AC so I can run my laptop and a pot of coffee when contesting mobile.  Ain't bad for an old disabled vet who has all this done by friends. and they work fine.
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AJ3O
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« Reply #12 on: February 23, 2013, 09:01:44 AM »

Note for the exhaust.

Bond it at many spots.
IE: If it is a large vehicle and the exhaust is long, bond it in at least 5 spots to cut down on noise. If is is a compact car, 2 spots might do.

The metal exhaust pipe from the engine to the tip is essentially a floating antenna as the exhaust is typically not solidly mounted to the frame but "Hung" with rubber and steel mounts. On a larger truck such as mine, the exhaust is almost 22' long. Anything over 3 - 4' on hf will resonate and affect your antenna system noticeably.

Visit K0BG.com and read. His info is just about the best.

73,

Joe / AJ3O
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KC8QVO
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« Reply #13 on: February 23, 2013, 01:19:26 PM »

Joe -

I discovered the exhaust pipe ground on my 2003 1/2 ton silverado, about 8 years ago or so. It made a huge difference in the noise level. In fact, one year when I was on my trip home from my place in Canada the noise level on the bands started getting worse and worse. When we stopped for the night I got under the truck and discovered that the strap had broke all the way off. I didn't have the materials with me to fix it that night, so I just put up with it until I got home. The subsequent vehicles I have had and installed HF in I have grounded the exhaust pipe as part of it - just in one location towards the rear of the truck.

My current truck is a 2011 CCLB F350 with the 6.7L powerstroke engine. I haven't even thought of measuring the exhaust pipe length, let alone more than one ground. In your experience - does it really make that huge of a difference? I understand the resonating properties - but that is why I grounded the one time to start with. I am really curious after your post if there is much merit to more than one ground. By using the one ground it shorts the "antenna" and, unless I am off my rocker, destroys the radiating ability. Wouldn't it be akin to shorting a dipole by jumping the legs together in the middle or towards the ends?
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