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Weird Issue, Need advise

Discussion in 'General CB Services Discussion' started by scotsmn30, Oct 21, 2021.

  1. scotsmn30

    scotsmn30 New Member

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    Hey there all, I have a Uniden PC76XL with a RM K-203-P, Stryker SRA-10 Antenna with 25" shaft to get above cab mounted to front passenger side bed hole, in a 2013 Chevy Diesel. The SWRs are running 1.3 to 1.4. The issue I am having is that the Radio and Amp work Awesome when the Truck is not running even with the key in the on position, but as soon as the engine starts, I lose all receive. I turn the amp off and I get the normal receive back on the radio alone. It does not seem to be affecting the output at all, just the receive.



    I put a dummy load on the antenna side of the amp and tested it and it worked just fine. I put the antenna directly to the radio and no issues. But Antenna to the amp and boom, no receive.

    Antenna is grounded to the truck and tested with a meter to confirm. Power to the amp and radio are direct to the battery with 8 ga wire.

    Looking for any suggestions on what I might look at for the issue.
     
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  2. secret squirrel

    secret squirrel Lustrous Potentate

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    Bear with me and try this. A lot of times we overlook simple things. Look at the coax connector on the amp and make sure the coax cable end mates up tight in the amp. A lot of times the connector becomes loose from inserting coax that has a touch of solder on the center ground. It causes the connection on the amp to spread a little when the mate up. Your ground will become intermittent and be interrupted. Also, double check your coax from amp to radio and make sure there is not a short, with your multimeter. Start with these ideas if you have not already. Best of luck.
     
    #2 secret squirrel, Oct 21, 2021
    Last edited: Oct 21, 2021
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  3. secret squirrel

    secret squirrel Lustrous Potentate

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    I am first to admit we have a tendency to over complicate things and overlook simple or obvious solutions in favor of more complex models. A great example would be needing to buy a new 6.5 Creedmoor rifle to hunt squirrel. Because the ballistic coefficient of the bullet and the flat trajectory would make a great long range squirrel rifle.
     
    #3 secret squirrel, Oct 21, 2021
    Last edited: Oct 21, 2021
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  4. freecell

    freecell Well-Known Member

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    "Power to the amp and radio are direct to the battery with 8 ga wire."

    eliminate the ground line from equipment to the battery and ground the equipment directly to the nearest vehicle ground inside the cab. make sure there is no excess length in the positive line from the equipment to the battery then try it again.
     
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  5. 9C1Driver

    9C1Driver Sr. Member

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    What freecell said. I have always grounded my amplifiers to a seat bolt or the firewall.
     
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  6. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Common SINGLE point ground for all your system should work.

    Essentially it's running a positive wire to each part of your system - from the battery (or terminal block if you're the type needing the ease and safety of using such).

    Ground (the return) is all the parts connected together - with one tie off to BOND to ground - chassis - as one single point - for grounding.

    upload_2021-10-21_20-0-41.png

    Some people (many really) use a Mag mount and can never truly be able to run this like it can be used, so that excludes the ones using Mag mounts like 'lil - Wil' and K40 or even Firestick types using the simple mag mount - so that puts those types of system at a disadvantage against a true-grounded system.

    So if you cannot ground at the Antenna (Best) Use Amp to ground ALL devices thru Coax Shield / Braid to itself as COMMON grounding point.

    Just keep the connections to power from two locations - preferably having the return to the longest distance away from the battery - this is due to "ground loops" that could form from multi-point grounding or bonding points where circulation currents can form and swamp out your Receive.

    So your Receive cutting out may be from the ignition system of the truck emitting a noise the amps' Pre-amp or because of its; physical location to a signal generated by the truck when the engine is running - can cancel out your receiver due to it.
     
    #6 Handy Andy, Oct 22, 2021
    Last edited: Oct 22, 2021
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  7. loosecannon

    loosecannon Sr. Member

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    i think you are wrong about the fact that you have receive with the amp on and using a dummy load.

    i think that the receive pre-amp transistor in your amp has gone bad.
    LC

    EDIT:
    you said this was a diesel.
    any chance you have two batteries and when the engine is started you are not connected to a battery with the amp?
     
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  8. Slowmover

    Slowmover Supporting Member

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    HA, in diagram you provided we have, “BOARD GROUND needs to be BONDED to CASE GROUND”; how to achieve (or, verify) this?

    1). More than running a bond to a case screw, correct? (Dumb Q out of the way; what specifics?)

    2). For an amp, what specifics? (Like the OP, am using an RMI amp).

    — I need to continue on my KW T680 install with this, it appears. Was already mentally re-arranging line placement in the overhead console on where to install a DC ground-point in the overhead console for main power to shorten circuit length, so this is timely. As in other threads, the truck I’m in is now the permanent assignment — install was quickly done on an ad hoc basis. (Lost starboard mirror heat power so that entire arm will be replaced once in shop. I may re-run ALL power and coax as a result).

    3). Am also thinking of using the MORGAN Bandpass filter again which has two (2) coax grounds (one IN and one OUT; before & after circuit); should “ground” be separate? Separate as it’s an RF BOND (only) versus attaching to the common DC Ground? (And should those two coax bonds be grounded separate from one another?)

    4). I’ll also throw in the more remote possibility of again using the MFJ 945e Mobile Tuner (has a provided ground stud) to be certain of not having left anything out.

    Common Ground Point doesn’t seem unambiguous, but truck driver assumptions can be the thing of legend.

    — Guessing I’ll need a tech to provide interior radio board to case DC ground, and what’s needed for RMI amp. (Drill hole for an exterior stud?)

    — And, if I’m gonna drill console (from underneath), I have to plan ahead.
    3, 2, or 1 ground locations.


    I welcome comments or advice from all.

    Thanks.

    .
     
    #8 Slowmover, Oct 22, 2021
    Last edited: Oct 22, 2021
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  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    @Slowmover - if you need to route a ground - SINGLE ground - then let the coax be that ground run using it';s shield - but in some radios - like the OLDER PC-76 and such - take a DVM and MEASURE in ohms Ω the NEGATIVE lead to the back panel of the radio (Case) if it's greater than 1K ohmic - you have an INSULATED BOARD ground - so you'll have to BOND Case to Board ground (anywhere you see those little board screws) that have a cap to RF bypass the board ground to case grounding allowing RF to flow back in forth but this generates a ground loop issue when you have more than one grounding place in your system (a noise problem)

    See below...
    upload_2021-10-22_10-10-28.png

    You only need and I highly recommend one spot close to the power input
    from your Uniden Power 3-pin connector...

    Try a straight run of coax for this first to see if issues arise - then try the device...​
     
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  10. Slowmover

    Slowmover Supporting Member

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    For my own understanding, is it meant a separate amp power line versus one common to all components?

    .
     
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  11. Slowmover

    Slowmover Supporting Member

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    887A394F-F000-4421-AF7B-F45CDD04F403.jpeg

    1). This, if ohm test indicates coax only? (These are sold as “Coax Lightning Arrestor” for those unfamiliar). What of amp?

    — Sorry if I’m stuck in baby steps mode as I’ve been on the highway for the last month.

    2). Overall — all gear mentioned — all RF & DC to the same ground point(?)

    — Keeping those bond straps shortest plus install/remove ease is a test in itself. Trial fits of gear, then cables (three sets) takes the most time; that, not in an abundance.

    Where
    to drill becomes the biggest Q.


    .
     
    #11 Slowmover, Oct 22, 2021
    Last edited: Oct 22, 2021
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  12. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Try to make the coax the connection go-to point for that common for BOTH RF and DC (Power) - since both are power but in different realms - I'm looking at this as personal experience in both my trucking days and to my own vehicles - Single Point Grounds are about the easiest and simplest ways to accomplish the power needs and cure several ill's that normally occur when the Ground of One - is better than the Ground of another - which then adds a level of complexity - which you don't want.

    Ok, you ask a multi-faceted question - one is being - with single point - where to ground?

    Well, the best is to use the exterior skin - but that doesn't always have the best or lowest level of chassis possible - sometimes it's in the truck itself (overhead of sub-structure) - but to be honest - use the coax and it's connection to the outside antenna ground - and for some in the Fiberglass and Carbon fiber realm, that puts you back to having to make the ground at the CONSOLE your have the radio and amp at - there's nothing wrong with this but you'll get unstable results if and when the RF ground used at the location of where the antennas are at - wants to find a quicker easier path back to the radio or ground.

    So with what you worked with in other trucks - still works here in your newer one too - just have to (behind closed doors) make the grounding bond points better for the exterior skin - and let your coax worry about the electrons wandering thru it

    Because of the potential differences of the ground itself (chassis) the reactive side of the equation can easily become unmanageable
    • - caused by RF ground being better in one location because it's closer to the antenna while another location is providing a better DC ground because it's closer to the battery return
    • - so you get this "Chemtrails over Coffee" effect that although noisy, makes the system seem workable, just not very well
      • - but to stabilize the grounding many just tack on wire and wire after wire...don't do that!
      • - the single point sources, trailing back to the antenna for Ground (longest run from the battery for Shield) and the shortest run from the Battery for Positive (power) provides the best in loss per foot of distance an electron must travel (if they really do) because of the SINGLE source, Single Return methodology works - you still suffer from Ohmic losses - but your system has a better balance of power draw as you use it.
    There have been ham books written on this subject for many years, but if you ever look at a properly grounded station - many bond their systems to a single point using a Buss distribution system to handle power and common ground - then let the electrons find their best, easiest path back and away from the station and operator - making it a safer system to handle with far fewer noise and ground loop issues.
     
    #12 Handy Andy, Oct 22, 2021
    Last edited: Oct 22, 2021
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  13. Slowmover

    Slowmover Supporting Member

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    89FC0581-B7F0-48C2-8A85-0AAA9BB11137.jpeg

    This is how I distribute 12V up in the overhead console of a Kenworth T680 from 6-AWG. (BATT is almost 20’ away). A POWERWERX PD75. (Online, or at HRO).

    My current proposition (having discarded console steel as “the buss bar” as I was doing):

    At present, NEG returns to the battery bank (temp install). No ground stud in overhead steel structure yet. Nearly 40’ something feet circuit-length.

    This device is a copper buss bar with APP connectors. Satisfyingly heavy for its size.

    -- A second PD75 to handle DC Ground + RF Bond is as far as I get mentally in doing a clean-up for Single-Point Overhead-Console Ground Stud in this KW.

    — Size of a buss bar matters. Other designs may be adequate (and cheaper), but the PD75 has both covered connections AND can be laid over flat, thus I could mount the pair on wood side-by-side such that would fit confines.

    — FWIW, installation/removal ease (speed + access) is important.

    1). 12V Neg Main jumper from original PD75 where NEG exits to the second buss bar POS connector. At other end of loop, NEG main out to console steel ground point. (A hole I’ll drill and use a SS screw + I/O star washer).

    2). Within that second buss bar loop, RF Bond straps from radio gear routed here as they have earlier intercepted the coax outer shield braid (or have bond studs).

    3) Each of the two antennas is about nine (9) feet distant, so installation of bond straps in quarter-wave lengths doesn’t appear as correct in connecting them to this device in the overhead.

    — With two antennas (cophase harness), going out from gear to mirror arms to bond doesn’t make sense either.

    4). Thus, the Overhead Console Ground winds up as one of three points for bond of the coaxial cable outer shield in a common reference.

    a). Overhead Console Bond
    b). Port Antenna Bond
    c). Starboard Antenna Bond

    I tend to “think” (loose definition, ha!) in terms of a parts list to get things done. Theoretical basis (versus hypothetical) may make sense (coax outer shield as common ground reference), but how else to achieve this isn’t. Best attempt, here.

    — As of this writing I don’t see a feasible way past the three-point problem due to distances involved. (The mirror arm mounts are bonded to cab structure steel about 18” away by woven strap as well as by designed truck construction. Same structure as for overhead console. Each antenna is bonded at the antenna feed-point literally against the PL-259).

    — Last, RF Bond of Amp & Transceiver cases is stuck in my mind. Power lines to each offer the 12V ground, but we see the recommendation often enough to add a jumper to the case for stray RF, nonetheless. That portion — valid or not — has me stuck in “how to?” as something desirable to achieve.

    — Other devices already have bond studs, but not this pair. Radio is a Galaxy DX-959b and amp is an RM Italy (one of several choices). What is best method to attach RF bond to each and thence to the second buss bar? As it seems this is sorta where we started.


    HA, your patience and effort are much appreciated. To the OP: I didn’t realize this would turn into a hijack, so I hope it is not far from solving the original Q. (Thanks).


    “His only tool is a hammer and thereby all problems are nails”, is what it’s like mentally as a truck driver out on the road when it comes to grasping new ways of accomplishing goals.

    .
     
    #13 Slowmover, Oct 23, 2021
    Last edited: Oct 23, 2021
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