Mobile Questions

Discussion in 'Mobile Radio Systems' started by KG4HNY, Dec 10, 2012.

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  1. KG4HNY

    KG4HNY Ham Member QRZ Page

    I just bought an FT857D for my soft top Jeep Wrangler. My plan is to mount a HamStick to one side of my rear bumper and a dual band VHF to the other. The bumper is aftermarket steel. I have read K0BG a handful of times and even sent him a PM here several months ago. I still have a few questions.

    I know mounting to the rear bumper isn't ideal, but I'm not left with many options. This is an offroad rig and the only flat horizontal surface is the hood. I really am holding to mounting on the rear bumper for several reasons of functionality not related to radio communication. What kind of performance can I expect with this setup?

    The next is another bonding question. I am a simpleton so please don't laugh. I trust the website gives proven fact. Please help me understand the logic. Why isn't the vehicle already bonded via it's original structure? For example, the tailgate is connected to the rest of the vehicle by the latch and hinges. To me, a strap seems to make just another one of those connections. Secondly, do you need to have a complete series of bonding to be effective? Let's say for argument that I bond only my tailgate to my inner tub and also bond my hood to my front fender. This would be different than, say, bonding my tailgate to tub, tub to exhaust, exhaust to fender, fender to hood. Is it imperative to bond a complete "circuit" or do I still get benefit of bonding independently if I have to. Why? I'm sure bonding everything is better. I am asking why, not whether or not it is.

    I really feel like I have taken in all this information but there are these small pieces of understanding that I still don't have. Thanks in advance for the help!

    This may be irrelevant but here is my bumper: http://www.aceengineeringandfab.com/ACE-JK-Rear-Bumper-with-Tire-Carrier_p_51.html
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Re "bonding," since these are add-ons, you can do one at a time to see what, if any, difference each one makes (once you have the rig and antenna fully installed and operational).

    The difference between a wide copper strap and the factory connections is simply "lower impedance for RF." What the factory does may make a good "DC" connection (or maybe not -- in many cases, it wouldn't matter) but their straps, springs, hinges and so forth aren't designed to be low-impedance RF conductors at, say, 30 MHz. You can improve those by using wide copper straps, and sometimes improve them more by using a lot of them.

    I've always started by installing the antenna and rig, first. Complete the cable connections and start measuring stuff, noting noise levels with the engine running, etc. Then, start "bonding" and take notes after each new bond is installed to see what changed.
     
  3. K0BG

    K0BG Ham Member QRZ Page

    Very sound advice from Steve (excuse the pun!). Did you install a common mode choke?
     
  4. K0BG

    K0BG Ham Member QRZ Page

    double post. Sorry
     
  5. KG4HNY

    KG4HNY Ham Member QRZ Page

    I have t started the install yet. Only the radio has been ordered. This is the preplanning phase.
     
  6. N7WR

    N7WR Subscriber QRZ Page

    I have had Jeeps myself and had to use the rear bumper on one side to mount an HF antenna (Tarheel II in my case). Worked fine BUT using several of the tips from K0BG's site to suppress noise was essential. Don't forget to bond the muffler/tailpipe especially if your antenna will be on the side where the exhaust is. If it were me, that is the first component I'd bond as I have had too many instances where everything else was bonded except the muffler/tailpipe and only when I strapped them with wide, flat copper sheeting did noise get significantly suppressed.
     
  7. KC9UDX

    KC9UDX Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    You're lucky!! My bumperettes will not support an antenna in a way that makes it usable!

    You are correct. The strap is totally redundant. It does nothing that the vehicle's bolts can't do. I think most people don't realise the size of the bolts. The problem comes in where you don't really get a good electrical connection between two parts bolted together. You have issues of surface corrosion (which you may or may not be able to see).

    The only way you're going to know if and where you need bonding straps is through experimentation.

    Incidentally, my YJ came from the factory with a lot of rather wide braided bonding straps. Unfortunately, I removed them long ago and replaced them with some expensive welding cable to make a really good DC path...
     
  8. KG4HNY

    KG4HNY Ham Member QRZ Page

    So what would be the point of using a grounding strap with factory bolts?
     
  9. KC9UDX

    KC9UDX Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Take your bumper off and measure resistance around the bolted area, of the bumper, and of the frame where the bumper bolts on. Measure the continuity of the bolts in various places. You will likely find it's not very consistent. This is DC. Imagine how much worse it is for AC.
    Granted, you may find that it's actually a very good DC path. You're still not seeing the AC path.
    The third possibility is that you have a good DC path and a good AC path.

    Which one of those three situations you have depends on age, luck, and rust-inhibitors. The less likely your Jeep is to rust, the less likely it is to have good conductivity at connection points.

    By adding bonding straps, you're adding potentially better current paths in parallel to the existing ones. In any case, that's less impedance.
     
  10. KA9MOT

    KA9MOT Ham Member QRZ Page

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