Jedi VHF/AIS station design

[dannc]

Thank you for this design and commentary.

Later,
Dan

[Jammer]

Originally Posted by s/v Jedi

I used to remove the coax from my radio until I got half electrocuted from the charge hanging in the air and caught by my antenna. When I moved the coax plug center pin towards the radio, sparks jumped almost an inch

This is why you should have a drain resistor so that your ground is not completely isolated. 1k is small enough to drain the charge and is large enough that you won't get any measurable difference in galvanic corrosion.

[s/v Jedi]

Originally Posted by Jammer

This is why you should have a drain resistor so that your ground is not completely isolated. 1k is small enough to drain the charge and is large enough that you won't get any measurable difference in galvanic corrosion.

I think you know that the isolated power supply has nothing to do with ground but then why do you write “so that your ground is not completely isolated” ? The ground in my diagram is not isolated at all, it is bonded to the Dynaplate.

If you propose to put a 1k resistor in those lines then you loose surge protection so I don’t understand where you want this resistor?

The static charge comes from the antenna and as I got zapped just on one hand that was unscrewing the connector from the radio, I guess the circuit was completed via the coax shield. But when I hold the center conductor, which was not arcing to the outer ring of the connector, towards the metal of the radio antenna connector, it arced at a comparable distance so maybe the charge to ground was higher.

When connected to the radio, the radio will take care of that and if it reaches a threshold then the gas tube arrestor will do that. Also, when the coax switch grounds the center conductor it’s drained to ground as well.

I have never experienced galvanic corrosion on my RF ground but I can see that happen easily when you connect stuff like DC negative, AC neutral etc. like some have

[team karst]

You do want a high value R from otherwise insulated antennas ref earth. I have used even 100kOhm. Otherwise very high values of potential can develop. I think marine auto-tuners do this too. Short vhf antennas dont seem to be as susceptible as larger hf arrays. This talks to draining off atmospheric induced static charge to avoid receiver damage, not strike mitigation. Sometimes done with a coil across the rf path. If an ohmmeter on the radio ANT fitting measures some conduction, then the static drain is built in. You can research precipitation static and the like which manifests itself as receiver noise.

[s/v Jedi]

Originally Posted by team karst

You do want a high value R from otherwise insulated antennas ref earth. I have used even 100kOhm. Otherwise very high values of potential can develop. I think marine auto-tuners do this too. Short vhf antennas dont seem to be as susceptible as larger hf arrays. This talks to draining off atmospheric induced static charge to avoid receiver damage, not strike mitigation. Sometimes done with a coil across the rf path. If an ohmmeter on the radio ANT fitting measures some conduction, then the static drain is built in. You can research precipitation static and the like which manifests itself as receiver noise.

Where do you connect that resistor? Between which parts of the diagram?

The antenna is not isolated? The diagram clearly shows it being grounded by the bonding plate.

I think you are talking about the coax center conductor? I have not yet seen any radio that doesn’t have this in their end stage, but a member just pm’d me a surge suppressor that also has a static bleed inductor as well as a DC blocking capacitor, which sounds like a very good plan.
https://www.arraysolutions.com/as-30...mME9sIzN_gtgoI

I think you misinterpreted my diagram. There is no antenna isolation.

[team karst]

Yes, the antenna is not ISOLATED. The outer shield is continuous in the system; ant to radio. But, the center conductor may be INSULATED from ground, thus this talk of bleeder resistor or L from center to earth.

The other confusing point is coax switch isolation. This measurement is an rf port relative power measurement. Take a 3 port rf switch. Port A is switched to port B. A power meter attached to port C will show a much lower rf level than what is present at A and B. 40dB down is a factor of 10,000:1. That is, 10,000 Watts applied to the active ports results in 1Watt on the OFF port.

[s/v Jedi]

Originally Posted by team karst

Yes, the antenna is not ISOLATED. The outer shield is continuous in the system; ant to radio. But, the center conductor may be INSULATED from ground, thus this talk of bleeder resistor or L from center to earth.

The other confusing point is coax switch isolation. This measurement is an rf port relative power measurement. Take a 3 port rf switch. Port A is switched to port B. A power meter attached to port C will show a much lower rf level than what is present at A and B. 40dB down is a factor of 10,000:1. That is, 10,000 Watts applied to the active ports results in 1Watt on the OFF port.

Yes okay, the surge suppressor I linked above had that static charge bleeder in the form of an inductor I was told and this is a good recommendation.

The isolation in the switch is a matter of shielding. There is no direct galvanic connection but there is RF radiation that is picked up at the other port because shielding isn’t perfect. At 60dB this is just fine but someone reported only getting 40dB or so. I suspect that non-genuine switches are being sold because this Japanese switch has been on the market for a long time. I don’t think the genuine product has that much units that fail to meet specs because normally Japanese products are pretty decent with that.

I will try to find tests for this switch and suppressors when they are exposed to transient surges. I actually expect them to do well. I have very good results with surge suppression at the place in Florida we have, where we would have multiple incidents per year and now everything has been okay for three years since I installed 3-level protection and all the gear is still showing green lights for health.

[S/V Illusion]

Originally Posted by s/v Jedi

Yes okay, the surge suppressor I linked above had that static charge bleeder in the form of an inductor I was told and this is a good recommendation.

The isolation in the switch is a matter of shielding. There is no direct galvanic connection but there is RF radiation that is picked up at the other port because shielding isn’t perfect. At 60dB this is just fine but someone reported only getting 40dB or so. I suspect that non-genuine switches are sold because this Japanese switch has been on the market for a long time. I don’t think the genuine product has that much units that fail to meet specs because normally Japanese products are pretty decent with that.

I will try to find tests for this switch and suppressors when they are exposed to transient surges. I actually expect them to do well. I have very good results with surge suppression at the place in Florida we have, where we would have multiple incidents per year and now everything has been okay for three years since I installed 3-level protection and all the gear is still showing green lights for health.

Apparently, you misread my comment about the port isolation of Daiwa switches. I didn’t say one I tested was 40dB but rather 40dB down from the other. They are duplicate switches, not some clone.

Unless you test what you have, there is no telling how well it functions in the real world.

Suggesting the failure observed is a result of some knock-off isn’t accurate. . I’ve been using coax switches for decades in ham radio.

[s/v Jedi]

Originally Posted by S/V Illusion

Apparently, you misread my comment about the port isolation of Daiwa switches. I didn’t say one I tested was 40dB but rather 40dB down from the other. They are duplicate switches, not some clone.

Unless you test what you have, there is no telling how well it functions in the real world.

Suggesting the failure observed is a result of some knock-off isn’t accurate. . I’ve been using coax switches for decades in ham radio.

Oh… now I’m really confused… so it was like one was 60dB and the other 40dB less so only 20dB? And it was the genuine product (how to tell?).

I think I can test this easily with my NanoVNA so l will report my findings. I think I’ll also order another one from Amazon to see if it tests right or not, maybe even open it when not to compare insides… before returning it

I would not be able to tell a genuine product from a knock-off and have no idea what the switch that I have is or even where it came from. I could still use one with bad isolation in this case because the other port is just a dummy load.

[team karst]

Up in W NY, the anti lightning capital of the US, my radio antenna suffered a direct strike. It melted one side of my ladder line, then came across my lightning “arrester”. It was made with a toroid L center to shield, a series capacitor, then a neon lamp center to ground. The puny neon exploded, the shunt L core lost its permeability , but ultimately conducted most of the charge to 3 ground rods. My receiver was connected, but undamaged (11 tube design). Lots of collateral mayhem throughout the house.

I forgot; why is a rf switch in the discussion?

[s/v Jedi]

Originally Posted by team karst

Up in W NY, the anti lightning capital of the US, my radio antenna suffered a direct strike. It melted one side of my ladder line, then came across my lightning “arrester”. It was made with a toroid L center to shield, a series capacitor, then a neon lamp center to ground. The puny neon exploded, the shunt L core lost its permeability , but ultimately conducted most of the charge to 3 ground rods. My receiver was connected, but undamaged (11 tube design). Lots of collateral mayhem throughout the house.

I forgot; why is a rf switch in the discussion?

Yes, direct strikes are devastating and safeties work surprisingly well. For a direct strike, the surge suppressors are self sacrificing, basically just establishing an initial path to ground, which the lightning bolt then expands as it sees fit.

That your receiver survived was probably just as much from it’s tube design as it was luck because just the transient surge through the ionizing and the air itself is powerful enough to do a lot of damage.

We were inside our boat during an evening night in Curaçao when lightning struck the boat at anchor next to us. Our hair was raised literally, also on arms during the forming of the leader and we heard a noise like a starting elevator before the big boom after which it got dark and quiet for a couple seconds before the lights came on again (DC!) and systems beeped in error or rebooted by themselves.

The switch in the diagram serves multiple purposes:

- allows complete galvanic isolation of the radio from the antenna center conductor without needing to unscrew the coax connector from the radio, which got me zapped.

- with the radio switched to the dummy load instead of antenna, the dummy load protects the radio against static charge damage, which got my expensive Kenwood radio zapped.

- allows an easy way to do testing and maintenance without needing to handle the big stiff coax from the antenna.

This in addition to the surge protection as well as the power supply isolation.

[S/V Illusion]

Originally Posted by s/v Jedi

Yes, direct strikes are devastating and safeties work surprisingly well. For a direct strike, the surge suppressors are self sacrificing, basically just establishing an initial path to ground, which the lightning bolt then expands as it sees fit.

That your receiver survived was probably just as much from it’s tube design as it was luck because just the transient surge through the ionizing and the air itself is powerful enough to do a lot of damage.

We were inside our boat during an evening night in Curaçao when lightning struck the boat at anchor next to us. Our hair was raised literally, also on arms during the forming of the leader and we heard a noise like a starting elevator before the big boom after which it got dark and quiet for a couple seconds before the lights came on again (DC!) and systems beeped in error or rebooted by themselves.

The switch in the diagram serves multiple purposes:

- allows complete galvanic isolation of the radio from the antenna center conductor without needing to unscrew the coax connector from the radio, which got me zapped.

- with the radio switched to the dummy load instead of antenna, the dummy load protects the radio against static charge damage, which got my expensive Kenwood radio zapped.

- allows an easy way to do testing and maintenance without needing to handle the big stiff coax from the antenna.

This in addition to the surge protection as well as the power supply isolation.

Haven’t read all of your comments but as long as the outer braid of the coax is electrically connected, it makes little difference whether the coax center conductor is isolated. You are half way there.

[team karst]

Originally Posted by S/V Illusion

Haven’t read all of your comments but as long as the outer braid of the coax is electrically connected, it makes little difference whether the coax center conductor is isolated. You are half way there.

Maybe. Maybe not. Invariably, radio “lightning arrestors” attempt to clamp all the antenna conductors together. Low tech designs use spark gaps to encourage a fault path. If you look at the base of am broadcast tower/antennas, you may find two largish metal balls some cm apart setting up a spark gap. Smaller commercial quality devices employ gas tubes, which have predictable breakdown V, independent of pressure and humidity.
But, in these cases, they are somewhat hampered by response time. Gas tubes take a microsecond to respond. All this said, having a short placed pre-strike from center to shield removes this time constant, and therefore is more effective.

[S/V Illusion]

Originally Posted by team karst

But, in these cases, they are somewhat hampered by response time. Gas tubes take a microsecond to respond. All this said, having a short placed pre-strike from center to shield removes this time constant, and therefore is more effective.

A testament to the practice of using true grounded switches grounding both ‘sides’ of the coax. Everything else is questionable window dressing.

[team karst]

Pretty sure B &W and DowKey did it right. Not sure about others.