How much is too much?

Ex, If I run LMR400 from Antenna down to base of tower and into Poly Phaser Lightning arrester, then LMR400 another 10' or so into the house almost to the radio, but plug it into a SWR meter, then run RG-58 from the meter to the radio say 3', would that RG-58 have to much loss???

How far can you run RG58 without a noticeable loss in signal? With PL 259/Male UHF connectors if that matter.

Power loss charts are for 100 feet of cable.

here is a calculator.

https://kv5r.com/ham-radio/coax-loss-calculator/

10 feet of RG58 at 146.0 MHz will lose 11% or 0.5 db.

10 feet of LMR400 will lose 3% or 0.15 db

RG 58 at 2m will have a 5 db loss per 100 feet of cable, ie 70%, the loss is linear with db so ( not with percent ),  50 feet will be 2.5 db and 44% loss

Better off going with RG8.

I don't disagree...

Really depends on what you're trying to do and how critical the application is. If you're setting up an EME station, sure, use a -400 size jumper. If it's for FM, I wouldn't worry about it. You could save a few fractions of a dB by going with low-loss -240 size cable instead of RG58.

The general rule of thumb is that it takes about 3dB in loss to be noticeable on FM, and 1dB or a bit more to notice on SSB.

For setting up my home base station, I plan to use LMR-240 for about 20' to get from my office to my attic.  From that point on, I plan to use LMR-400.  My conservative estimate is that I'll have about 75 feet of coax from the radio to the antenna, including the surge protector route.

I'm forced to have my shack on the 2nd floor, with easy cable access out the window right next to the shack desk.  No option for having the shack on the 1st floor.

So I have to run coax from a 2m/70cm antenna at its position above the roof eave (about 25' or so off the deck), down to my exterior ground panel that houses grounded surge arrestors (which is about 5' off the deck), then back up to the 2nd floor shack window and in to the shack desk.  So let's say 45' total cable run.  

Should I do RG8 or LMR400UF?  Max 2m/70cm transceiver power is 50W.  The cable will have to flex a fair amount in the surger arrestor panel.

That's no big deal.

No you don't. That's not a good way to do it. Bring up some 6AWG stranded from the ground rod to the window location and mount your lightning protection there. Then your coaxial cable runs can be very short.

6AWG copper stranded is what utility companies use to ground lightning rods on the top of utility poles. Good enough for them, good enough for you and me.

If you don't mind the extra cost, LMR400UF is always going to be a superior choice, especially if it's legit Times Microwave and not a clone. I even use it for short runs just because I like the quality of the cable. But the reality is, if you take my (free ) advice above, it's going to be such a short run that it really doesn't matter.

As a rule, I hate to see more than 1.5dB loss on any run. Unless you start to get into things that are exotic, that pretty much means LMR400 and a max run of 100ft on 2M, and 50ft on 70cm.

That was my original plan as well:  Mount a ground wire and coax ground block on the bottom of the mast at the gable end of my roof.  Take the coax directly into the attic, while a 6ga ground wire goes down to the SPG.

However, I was watching a video yesterday that said that that plan was not a good plan.  He recommended grounding the mast and taking the coax down to the SPG to a grounding block with surge protector, then the coax back up to the 2nd story, very similar to what Jimmy wants to do.

Here is my current plan, note that it pretty much follows your recommendations.  I have the ARRL grounding book on order; it will be interesting to see what it recommends.

Thanks for the help!



ETA:  Note Gamma762's comments on the my above plan in this thread:  https://www.ar15.com/forums/outdoors/More-2m-Antenna-Questions-advise-and-pic-requests-/22-701516/?r=-1&page=1&anc=12036729#i12036729

You can certainly believe who you want. I don't know what video that is, but obviously I'm not in agreement with it.

From a purely theoretical standpoint putting the lightning protection directly onto the ground rod is obviously superior. One cannot argue that such a path is shorter and lower resistance. But from a practical standpoint the difference is immaterial. If it was not, then we'd be losing utility poles to lightning at a frightening rate.



That won't be the first time Gamma and I have disagreed

Everyone has to find their own salvation. I have had extremely good experiences with the configurations I recommend, and I've adopted them based on the logic I've described. I used to run a Winlink RMS station 24/7/365, damn the torpedoes and the lightning, it was NEVER off the air. My current station pretty much runs 24/7 and is never disconnected from the antennas either. In the last 15 years I've lost 3 Morgan (used to be "ICE") lightning protectors. Each gave up its life as designed. So I'm taking some kind of hits and have been OK.

Just remember that the sort of things we do will never survive a direct hit. You need to meet Motorola R65 standards for that level of goodness. How many live inside all metal buildings, or have put up air terminals (lightning rods) around their antennas? Nobody I know!

Surge protector can't force a surge to go one way or another, all it does essentially is create a temporary short circuit. From there, where the surge energy goes just depends on impedance. If the surge protector is that far away from the ground system, the relative impedance of the path to ground compared to the coax going into the house will be such that a notable percentage of the energy will just continue to follow the coax. Since the antenna is (probably) DC grounded just a few feet away, the surge protector really isn't doing anything if located up high... if you do that, just run the ground wire down and forgo the surge protector.

That's not correct. Lightning is an impulse. The standard lightning impulse used for modeling has a 1 to 2 µS risetime, and 50 µS fall time. That's pretty close to DC. The impedance of a 6AWG stranded wire is going to be nil at that speed, and it will not choose coax preferentially. But even that argument is moot since the gas discharge tube will start conducting very quickly and works in concert with the very strong impedance presented by the capacitors and inductor. Thus no energy will get onto the coax to speak of.

Here's a couple of photos of the inside of one of my old, damaged Morgan units. The antenna goes to the GDT side, the radio goes on the static drain resistor side. I need to get off my butt and repair the thing. It probably just needs a new gas tube or capacitors (or both!)

Attached File


Attached File

Guess what?  Both can be right and both can be wrong and both can be right and wrong at the same time.  With the energy involved and potential for plasma which does not always follow the normal rules of physics, there is no way to predict what WILL happen with a lightning strike.  A friend of mine witnessed a strike less than 100 feet from his point of observation, it was not a fraction of a second event. This event involved a wooden hulled sailboat docked at a bulkhead and was observed from a second story office window across a small parking lot, he was at eye level to the strike.   I have read that there are sometimes multiple pulses in a "strike" and sometimes "counter strikes" within a single event.

The only way to avoid it, is to be somewhere else.

Yeah I really need some help on this.  I know to minimize the feedline runs as much as possible.  On the side of my house where the shack window is, that's also where the main entrance panel and 2 original ground rods are.  I have driven 3 new rods, separated by 2x their length, bonded them with #4 solid copper, and bonded that to the entrance panel ground with #4.



I have that book, have gone through it 2x, made notes, and followed up with online research.  I think when you read your copy you'll find that they recommend having a 1st floor shack if at all possible, and to keep the connection from your surge arrestors to the ground rod network as short as possible.  If the distance between your arrestor panel and rod network is short enough, they say to use 2" copper strap in order to maximize the conductor surface area and take advantage of the skin effect.  It would be even better to have your arrestors mounted at the top of one of the ground rods.  But I don't see how I could fully weatherproof that.  I like the idea of a protective arrestor panel, but I don't like the cost.

When it comes to handling surges, it's all about minimizing impedance to earth ground.

However, I have gleaned a few things from my learnings.

A) the 3 grounds are 1. equipment safety ground, 2. RF ground, and 3. surge/lighting ground.  #1 is taken care of by modern 3-prong grounded outlets.  #2 isn't so big a deal these days as compared to 40+ years ago when many homes did not have any sort of safety ground and the often homebrewed ham gear could have odd stray voltages.  #3 is what we've talked about above, providing a low impedance path for surges to get to the ground rod network.

B) It's accepted that we can't stop the damage from a direct strike.  But there's plenty of lighting events that can jack you up well short of a direct strike.

C) I have learned to listen to guys like aa777888-2 and accept that the real world is different.

But I still can't decide where to mount my surge arrestor panel, and thus how long the cable runs will be. :(

It's not so much that the world is different. But never let perfection be the enemy of good enough. All the texts will tell you what's perfect, but few resources will advise on what's good enough.

With my station now located in the basement my lightning protection is Morgan arrestors on a Morgan ground rod mount. I weatherproofed it by simply dropping a Rubbermaid container over the top of it to keep the rain off. That's worked fine for going on 6 years or so. If you decide to go in this direction that's the "good enough" solution. No need for a fancy box.

I have R56 training next week...


I'll check back after that

I have some in outdoor installation that were just coated in Plasti-dip that have been in service for over 10 years. Which reminds me that I should go check on them.

Someone may say, well that's not going to protect me from a direct strike, but it's better than nothing, I'll drive in a couple of ground rods here, run a ground wire over there, etc.

The problem is that a half-a$$ed installation of extra grounding stuff can actually create RFI problems and electrical safety issues. It's pretty easy to create a ground path through the ham station that's very hazardous. Things get complicated in a hurry. I'm not saying don't ground anything, I'm just saying that folks need to take a step back and look for the unintended consequences.

Read this 12 page thread over on QRZ last night and this morning.  A whole lot of disagreement with a lot of the same comments as here.  However, it appears the consensus is to have the coax go to near ground, surge protect it with a conductor to the SPG and then go back up.  

https://forums.qrz.com/index.php?threads/where-to-put-the-surge-protector.656080/

ETA:  When is someone going to fix the goddam hot link "function" on this site?  

It was a Dave Casler video; unfortunately I can't find it at the moment.

I don't want to design my shack based on beliefs.  I want to base it on Best Practices.  Everything I'm reading says to take the coax to near the SPG, so that's what I'm going to do.

Here is my latest design.  Note that I ground both the antenna mast and coax shield at the mast base.  Also, I went to #6 ga copper wire, since I can get it in 100 ft lengths and it meets the minimum.



As far as extra coax required for this design is concerned, the difference is readily seen above:  It's basically the two red lines below the "Coax In" text box.  Once in the attic, the coax will run down the length of the house to the fourth porch post, about 20 ft, then drop to my office.

What is really critical when you add grounding like that is that your grounds... grounds that you are adding, along with the existing electrical safety ground, telecom/cable ground, cold water... are all bonded together OUTSIDE the house. Because if they aren't, your ham station becomes the bonding, which you do not want. Your ground is right there at the electrical entrance and you mention bonding so this is good, but for someone else considering something similar any new ground rods you add need to be connected to existing grounds with a heavy gauge wire/strap.

Exactly, that's what the blue text box refers to.

Also, I'm not depending nor considering the existing (maybe) home electric utility ground rod.  I'm just going to assume it's not there or, more likely, is only driven 3-4' at most.

I lived at my last house (which I had built) for over 5 years before I discovered the two #4 copper ground wires from my two breaker boxes were grounded to - thin air.

My neighbor next door accidentally ran over one of his ground rods and bent it; he asked to help him fix it.  We tried to disconnect the ground wire and compression fitting.  While trying to pull the fitting off, we pulled the entire ground rod out of the ground!  It's length was less than 2'.  

I'll connect to mine just like the NEC, Motorola R56 and probably the ARRL book require, but I'm not counting on it.

exactly

everything is a ground path.

but some are better than others and most are only temporarily in nature

a strike will take the least impedance ground until it isnt and then find the next one

The 8 foot circle of dirt around a ground rod acts like a capacitor when a bolt starts using it to go to ground because the ground simply can not absorb a strike charge fast enough. a charge builds up in the dirt just like on the plates of a cap

then it finds the next lowest impedance etc etc

I remember an instructor in Jr College telling us that there could be enough voltage differential along the ground to kill livestock because the difference in voltage from their front to back legs was enough to cause current flow that would kill them. How well done the meat might have been was a topic of speculation in class that day.

Found this pic somewhere in the QRZ thread mentioned above.  Makes sense to me:

Thanks for that graphic.  Now I understand why shacks should be ground floor or basement.  

No matter how hard you try, the voltage at an elevated shack will NEVER be zero.  The riser from the ground rod to the shack will be in some way parallel to the wire coming down from the antenna and will have some induced voltage during a strike.  It takes only the tiniest bit of that MILLION volts to be a problem in your shack.

Back to the cable loss issue, I found this over on the Quicksilver radio site.  Thought it might be interesting to post it here.



Note that the "USA-XXX" cables are their house brand versions of the standard LMR-XXX coax cables.  According to them, most LMR-type cables are made overseas (read China); their USA- versions are US made.  Have no clue to the veracity of the claims.  Anyone here know anything about Quicksilver?

https://qsradio.com/shop-now.html#!/Coax-&-Ladder-Line/c/8424427

Looks like they're selling Davis RF cables, Davis OEMs for various vendors such as the Wireman.

https://www.davisrf.com/coax.php

Times-Microwave has a loss calculator on their website that has all their cables plus most standard/milspec type cables for comparison.

https://www.timesmicrowave.com/Calculator/Embed

Except that it describes no modern cell tower at all. Modern cell towers have the radios at the top, not the bottom. And a fair bit of other radio technologies, as well. So how do they do it if that picture is correct? Because it is not correct. Strategically placed impedances prevent it, and strategically placed lightning rods, too.

And the tower is not a factor. The impedance of a tower is much higher than that of a 2 or 3ft piece of coax. Which is why arrestors are needed to provide the strategically placed impedances.

Cell towers and lots of "high rise" installations.

Here's the thing. It's ok if your radio is at 10,000 volts, or 100,000 for that matter, as long as every connection to the radio is also at the same voltage. Slavish devotion to single-point grounding and surge suppression is required. And that only protects the station... in the case of a home, you also have to worry about the rest of the home and contents.