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Astron PS and Your Ground

Discussion in 'General Technical Questions and Answers' started by AI5DH, Oct 29, 2019.

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  1. AB6RF

    AB6RF Premium Subscriber QRZ Page

    The transformer secondary side has nothing to do with this.
    You could remove the whole transformer, and still the AC safety ground is directly connected to the coax braid right there at the back of every tube amplifier.

    https://i.imgur.com/fkj6Tra.png[​IMG]
     
    WR2E likes this.
  2. N8VIL

    N8VIL Ham Member QRZ Page

    I agree with having the DC negative being isolated from AC mains ground for the simple fact that if the DC negative cable became open from the power supply to the radio, I would not want the radio getting its negative return path through coax or other accessories through the AC service grounding. With the negative terminal isolated from PS chassis ground you would know if the negative connection to the radio was open. Radio would not power on.
     
  3. AI5DH

    AI5DH Ham Member QRZ Page

    Nor would anyone else if given a choice. You understand the loop and know DC current will be flowing through your coax shield. A small amount during RX Stand-By and much higher in TX. It has to because it is in parallel with the neg PS conductor. Does not matter if the DC cable opened or not. There will be current on the ground circuit. If the DC conductor opened, then all current uses the coax as the return path. When the cable is solid. a small amount current still flows through the service ground.
     
    Last edited: Oct 30, 2019
    N8VIL likes this.
  4. AI5DH

    AI5DH Ham Member QRZ Page

    There is also another negative effect of allowing DC current to flow on your ground electrode system. You get a Galvanic Corrosion on your ground system accelerating corrosion and failure.That is why Telephone companies bond Positive to ground to eliminate galvanic corrosion.
     
    N8VIL likes this.
  5. AI5DH

    AI5DH Ham Member QRZ Page

    Beg your pardon. The transformer has a lot to do with it. I agree with you a Linear Amp will bond the AC and RF Ground together. That will allow AC Current to circulate. However if the jumper is removed in the DC Supply, no DC current can circulate. With the jumper in, would allow both AC and DC currents to circulate. So yes the transformer has something to do with what will happen either way. So if you remove the jumper in the PS. it will block DC current and eliminate galvanic corrosion on you ground electrode system.
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    I calculate the resistance of 2ft of #8awg (the black lead between the supply and the radio) as being ~2 mOhms. At 20A, that produces a 40mV drop.

    Now consider your second (parallel) path: 5ft of green #14 wire in the line cord, 30ft of #14 Romex (bare copper conductor) to the panel, 5ft of #6awg to the panel's ground rod, 30ft of #6 in the cross tie, another 10ft of coax shield to get through the house wall back to the rig. Ignoring the resistance of several screw/clamp connections, the total resistance is ~120mOhm, which is 60x the 2mOhms in the black jumper. The voltage across this second path is 40mV, so the current is 40mV/120mOhm = 333mA

    Let's see, 20A goes down the black wire and 333mA arrives at the rig via the external path. Hardly something to get worried about! All the external path did is lower the impedance of the black wire from 2 mOhm to 1.967 mOhm.

    I say it again, you are making a mountain out of a molehill. It matters not at all if the grounding jumper is in or out!
     
    Last edited: Oct 30, 2019
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    BS. The 40mV that is dropped along the black wire between the Astron and the ham rig is the forcing function for the supposed Galvanic action. You must have failed Chem 101 and/or never looked at the Electromotive Series Table. Find me any reaction that is driven with only 40mV applied?

    ...and, the 40mV is only present on SSB voice peaks. During receive, the drop along that wire is more like 4mV.
     
  8. W5UAA

    W5UAA Ham Member QRZ Page

    I remember a few years ago, when I was at Kunia, when ever I went up to one of the antennas I had to check on regularly, I passed the station ground. One day, I brought a current clamp meter and measured just under 2 AMPs flowing straight to ground (or from ground... I don't know which way). Of course, this station ground had probably somewhere in the neighborhood of between 1,000 and 2,000 computers, radios and other assorted specialized electronic equipment attached to it. I was responsible for somewhere between 300 and 400 of them. My point is, unless you use extremely tight scientific methods in an extremely well controlled environment, there will be current flowing to/from ground. Even in the dense electronics environments I've been in, with specialized electronics folks following all known electronic/electrical standards and being inspected at least annually, there was current flowing to/from ground. Today, the first thing an adventurous new ham "homebrewing" his first computer to radio interface seems to learn is what a "ground loop" is, since there's one created with just about all first "homebrew" computer to radio interfaces. They learn quickly what it does to your outgoing transmitted signal.

    Haven't used an Astron in several years now. Never knew of this negative lead bonding thing with Astron. Never caused an issue with me when ever I delved into the computer to radio modes.
     
  9. KD0CAC

    KD0CAC Ham Member QRZ Page

    Interesting have to follow .
    But reading through this , at least in my mind a little related is isolation transformers / variac , on the inside the primary & secondary are tied together .
    I've looked into this a little when putting together a repair bench , oscilloscope etc. and the need for differential probe ?
    Not as versed , but it would seem that is I disconnected the internal ground between the Pri. & 2nd - that that would accomplish the same issue - using oscilloscope on AC line , with scope plugged into variac ?
    Holding off on such till I can afford a differential probe & or confirm the internal ground issue ?
     
  10. AI5DH

    AI5DH Ham Member QRZ Page

    I will say again you are missing the point and made my case for me. Thank you for that.

    Since you did not hear yourself, you admitted there is a voltage gradient along the ground path the loop forms. You said it not me, you calculated 40 mv remember? You have knowingly, willfully, and approve of injecting a unwanted signal into your 0-Volt reference. That is why you do not want any kind of current flowing in you ground circuit. It produces a voltage gradient along the length aka noise. The DC offset is not that much of a big deal because it does not get picked up and amplified like AC. By having the jumper in you also invite circulating AC currents which show up as 60 Hz from utility leakage of a multi-ground-neutral distribution system. AC voltages will be higher because now you have to add in reactance on top of resistance. The AC circulating current can be detected, picked up, amplified, and heard in both TX and RX audio and cause bit errors.

    All I am telling folks to do is if they do not like the possible consequences of a design flaw Aston has built into the product line, you the user can fix it. There is nothing positive to be gained leaving the jumper in and a simple test to know if your Astron has the jumper or not. You claim yours float, well go put the jumper in. :p
     

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