What does your setup look like?

[retman1222]

i could use some education here, i had thought that the GDT should be outside the building and go to ground prior to the cable entering the building???

[wiedehopf]

Honestly these gas discharge tubes won’t stop lightning really.
They are meant to protect the electronics from static electricity connected to lightning in the area.

I’d expect everything to be fried from a direct lightning strike hit.

[geckoVN]

Thanks. Hadn’t spotted them until you mentioned the earth cable.
The SDR’s have input protection diodes that will clamp a modest voltage.

GDT’s are great, but also have some drawbacks.
They are (relatively) slow to respond and the “kick in” voltage depends on the gas used. The down side of this is the voltage front may peak to several hundred volts before the arc lights up and clamps the voltage. Even then, the clamp voltage will be 20V which may be enough to blow the protections diodes if they’d survived the original spike.

bourns_understanding_elusive_vfp_and_effects_on_surge-protection.pdf

[foxhunter]

@wiedehopf

I’d expect everything to be fried from a direct lightning strike hit.

I thought about the same saying how can this tiny thing protect the devices from a strike.

Now i have my device outside connected to a lightning strike protector to avoid that a strike goes further into the house electricity.

I might loose the Raspberry, but fine with it.

[SoNic67]

Is evident that those suppressors are only to protect from induced voltage effects of a strike, not a direct hit. Like a strike on the HVAC units close on that roof or a near-by strike.

A direct hit won’t make it fully inside the building, the cable ground itself would be “jumped” trough the insulation to the nearest ground point (like building beams under the roof membrane). Roof membrane can catch fire. Metallic parts thinner than 3-5 mm would be melted (that’s why any HVAC unit needs strike devices).

Residual voltage on the cable would still be in KV range and damage everything downstream. That’s why building lightning protection strike devices and building ground conductors to ground are essential. In US, by code (NFPA780), every building with installed lightning protection has to be provided with SPD’s on power panels and comm cables entering the building. Induced voltages from 25-100 kA strike currents are significant.
The peak values of currents which can be exceeded with 50% probability are: 31 kA for negative lightning (first stroke) and 35 kA for positive lightning. The peak values which can be exceeded with only 5% probability are: 69 kA for negative lightning and 250 kA for positive ones. Generally, as higher object is, the higher the lightning’s current value is.

[abcd567]

@wiedehopf

I’d expect everything to be fried from a direct lightning strike hit.

A gas discharge device or even a disconnect switch or physical disconnection will not guarantee protection against a direct or close strike. A small air gap of few inches or even few feet, will not stop a lightning bolt that has already jumped across miles of air between cloud and ground.

 

 

@abcd567

2. Lightning and Surge Protectors for Electronic Equipment

Lightning protectors, Surge protectors and UPS units provide good degree of protection of Electronic equipment from voltage spikes from everyday power surges, static build up, and distant lightning strikes .

However when lightning strikes a building directly or very close to it, lightning/surge protector simply cannot have any effect on the tremendous amount of currents and voltages involved. Lightning current in a direct hit is simply too big to protect with a lightning discharge device, or a little electronic device inside a power strip, or a UPS unit. The lightning will just flash over or through the device.

Even a disconnect switch or physical disconnection will not guarantee protection against a direct or close strike. A small air gap of few inches or even few feet, will not stop a lightning bolt that has already jumped across miles of air between cloud and ground.

[foxhunter]

@SoNic67

A direct hit won’t make it fully inside the building, the cable ground itself would be “jumped” trough the insulation to the nearest ground point (like building beams under the roof membrane). Roof membrane can catch fire. Metallic parts thinner than 3-5 mm would be melted (that’s why any HVAC unit needs strike devices).

Thanks for the explanation.

[abcd567]

@SoNic67

That’s why building lightning protection strike devices and building ground conductors to ground are essential. In US, by code (NFPA780), every building with installed lightning protection has to be provided with SPD’s on power panels and comm cables entering the building. Induced voltages from 25-100 kA strike currents are significant.

@abcd567

How Much Power A Lightning Bolt Contains?

Lightning bolts carry from 5 kA (5,000A) to 200 kA (200,000A) and voltages vary from 40 kV (40,000V) to 120 kV (120,000V). If we take an average bolt , with current 100 kA and voltage 100 kV, this average bolt will carry power as calculated below:

Power in an average bolt = 100,000 A x 100,000 V
= 10,000,000,000 Watts or 10 Billion Watts .

 

 

@abcd567

Components of Lightning Protection

(1) Building Lightning Protection System (BLPS) for the Protection of Building and Persons Occupying it.
Consists of:

1. Lightning rods on roof
2. down conductors bonding lightning rod to earthing rods
3. earthing rods.

(2) Lightning & Surge Protectors for Electrical and Electronic Equipment:
Consists of:

1. Bonding of the antenna and dish mounting hardware to the building ground
2. Bonding the incoming coaxial cable sheath to the building ground
3. Surge/Lightning protector at antenna and dish coaxial cable entry to building
4. Surge protectors on the AC power wiring
5. Additional surge protectors on signal wiring
6. Supplementary “Point-of-Use” surge protectors at the equipment to be protected.

[tbeid970]

I experimented with different setups and finalized one in my attic. When I tried to cleanup everything by coiling the coaxial cable, etc. (see attached picture) my positions reported numbers dropped off by about 50%. The number of aircraft reported beyond 50 miles dropped to close to zero. I have since uncoiled the cable and separated things more and then numbers are back up.

Does this make sense to those of you that understand these things?

[SoNic67]

My guess: Something is not right with the cable connectors or even cable itself. When coiled, you put stress on them and they probably separated, hence the reduction in numbers.
Also, that antenna is supposed to be oriented the other way around, with ground lower than the rest.

[wiedehopf]

@tbeid970

Does this make sense to those of you that understand these things?

You’re putting all the noise generated by the electronics back into the natenna.
You have some coax, just use it to get the power supply / RPi / SDR below / further away from the antenna.

Suspending the antenna by it’s top part and having it just hang down will likely provide better results but that’s not as critical as the other thing.

[geckoVN]

The cable you are using is RG58.
Ok at lower frequencies, but too lossy for microwaves.

Either replace it entirely or cut it short and re-terminate.

[abcd567]

@geckoVN

The cable you are using is RG58.

Sharp vision

[wiedehopf]

@geckoVN

Either replace it entirely or cut it short and re-terminate.

I’d say it’s short enough.
Not great, not terrible.

[geckoVN]

@wiedehopf

I’d say it’s short enough.
Not great, not terrible.

I get what you are saying, but the performance changes if the cable is moved - maybe connectors or perhaps the assemble was poor.
Either way, it needs to be repaired or replaced. If it is to be replaced, I’d go for something better than RG58.

[FeverBeaver]

You’re right, but for (very) short lengths it should not be a major issue.
What is very short depends on your installation. I run 1.5m (4.5ft) and it only brings a minimal attenuation (quickly 1dB at worst case, as it is given for 18dB @ 1GHz per 100ft).

[tbeid970]

Thanks for the reply. I’ll get a new, shorter cable and try that. I knew the antenna needed to be mounted vertically, but didn’t read anywhere that there was a top/bottom issue in the orientation.

[tbeid970]

I’ll try those suggestions. Thanks.

[tbeid970]

Thanks. I’ll get something better than RG58; and shorter.

[abcd567]

@wiedehopf

Suspending the antenna by it’s top part and having it just hang down will likely provide better results

My FA Antenna Indoors, near a window. Suspended by a string tied to top of antenna. Performs very well.