1.5 KW Amplifier Off Grid

Running a full kilowatt from battery power has it’s challenges. This note steps through the design and installation of the amplifier, inverter, battery bank, and solar panels. First, the amplifier. It is a Flexradio 4O3A PGXL. To reach 1500 Watts output it requires 220 Volts AC. It does not run on DC. Here it is waiting for some AC while sitting next to the Flexradio 6600 exciter .

The next item is the inverter which provides the AC. A Victron Energy model Phoenix Inverter Smart 24/3000 has been chosen. It provides 3000 watts at 230 volts when connected to a 24 volt battery. This inverter was chosen because it has RFI certification, a reputation for meeting specifications, and it was less expensive than some others.

Next component is the 24 volt battery bank. LiFePO4 lithium ion batteries were chosen, of course. The capacity of each cell is 180 AH. Sixteen cells are connected in parallel/series to provide 24 volts DC with a capacity of 360 AH. Aren’t they pretty?

Finally, the solar panels. This array is four 100 watt panels wired in series/parallel to provide enough voltage and current to charge the batteries.

It really works! This is the control panel on the amplifier. Notice the output power is shown in the upper left corner, 1512 watts. Id is the current on the drains of the LDMOS finals, 43 amps. It is also nice to notice that under the load of a full kilowatt the inverter is holding the AC at 228 volts. With no load the voltage is 230 volts which means only a 2 volt drop at full output.

A clamp-on ammeter on one lead of the AC shows 9.3 amps of current.

One concern during the design phase was whether the AC connector on the amplifier was heavy enough. It is only a type C13 which is a 10 amp connector. Today’s measurement of 9.3 amps and the fact that the connector stayed perfectly cool to the touch is reassuring.

Next a look at some of the “glue” holding the stages together. The batteries are protected by a BMS. BMS stands for Battery Management System. It’s the big red thing. It will cut off the power if the voltage is too low or too high and it will try to keep the cells balanced. Electrically it goes between the negative terminal of the battery and the negative lead to the inverter. One small red wire goes to each cell to keep track of the state of the cell.

To the left of the BMS is the shunt resistor for a Victron battery monitor. A battery monitor is not required but makes it easy to keep track of the battery’s state-of-charge remotely. The black thing in the upper left corner is a terminal block. A copper strap connects between the terminal block and the shunt resistor. These items together make up the negative leg of the circuit.

In the positive leg there is only one component. That is a 250 amp fuse. Victron specified big 1/0 cable for the inverter DC power, and specified the 250 amp fuse.

One other piece of glue is the AC circuit breaker. A GFCI breaker is connected between the inverter and the amplifier to protect the inverter from overload and to protect humans from electrocution. It is 16 amp 240 volts. Don’t hunt for this unit in the 2020 NEC code. It is not a product designed for the U.S. market. It is designed for the 230 volt standard in Asia and Europe. This project is using European standards rather than U.S. The main difference is this is not “split phase” as in the U.S. which means there is no third wire on the 220 volt circuit. Why is it done this way? Because with the U.S “split phase” wiring a second inverter would be required to get the third wire, approximately doubling the cost. There is no safety or any other reason not to use the European standard. This system is entirely off grid and therefore NEC code is not required. Safety is a big concern and all European standards have been adhered to for safety.

Some observations

Sizing and the capacity of the components is a big part of any design. Today’s numbers provide some insight. The amplifier was drawing 9.3 amps AC at 228 volts. That’s 2120 watts (watts instead of VA because power factor is assumed to be 1 due to automatic PF correction, so watts and VA are equal). The amplifier was producing 1514 rf watts which is an efficiency of 71%. This calculates to 92 amps DC from the batteries (unfortunately no dc reading was taken). Looking next at state-of-charge (SOC), good practice for LifePO4 batteries is to limit depletion to 20 per cent SOC. That is, operate with SOC between 20% and 90% which provides 70% of rated capacity. Usable capacity would therefore be .70 X 360 AH or 252 AH ( or 6678 watts at 26.5 volts). Under a constant load of 92 amps the batteries would be expected to last 2.7 hours. With a 50 per cent duty cycle mode like FT8 the batteries should run at least 5 hours. There are no plans to operate at 1500 watts on FT8. This is just a worse case example.

Concerns would include whether the 4-panel solar array (400 watts) is adequate to maintain this large battery. That would not be the best way to look at it. Consider instead whether the array is adequate to provide typical amplifier operation. If the amplifier is operated two hours a day at 50 per cent duty cycle that would use 92 amps ( or 2438 watts at 26.5 volts). The panels generate about 2 kw on a good day (400 watts X 5 hours of sunshine). That is close to the 2.438 kw of typical usage. Good to go. On cloudy days the batteries are oversized so they will have capacity to operate for more than one day without sunshine. Winter is close and some hard numbers will soon be available. If needed the existing PWM charge controller could be replaced with a MPPT controller for 30 per cent more output. After a few weeks of operation in November the batteries have recharged to 90% every day when there was sunshine. As of late December during the solstice all is still functioning well.

A lot of effort and expense went into this project but it is proving that running a kilowatt from batteries off the grid is possible.

November 22, 2020 – The amplifier has a problem. It is refusing to transmit on all bands except 160 and only puts out 500 watts on 160. This problem started after receiving a message that SWR was too high and the amp should be shut down. The amp was quickly shutdown but has not worked correctly since. It was connected to the A3S antenna on either 15 or 17 meters when the failure occurred. Possibly the amp was putting out too much power for the A3S and a trap shorted out. Apparently the amp’s protection circuits failed. A ticket has been opened with Flexradio but Covid and Thanksgiving have delayed the response.

December 12, 2020 – Amplifier is fixed and back in the shack. Flexradio’s warranty tech support is amazing. They requested a remote test and determined from the results that it needed new finals. The amp was shipped to Austin, repaired at no charge, and shipped back in two weeks time. What a quick turnaround. Kudos to Flexradio.

The finals are MRF1K50H LDMOS transistors each rated at 1.5 kW dissipation. Mouser has these listed for $900 each in single quantities.

Update – June, 2021: The amplifier system made it through the entire winter without any power problems and all worked as designed. To avoid destroying any more final transistors FRStack3 was installed. FRStack reduces the exciters output power when an amplifier is placed in operate mode, protecting the finals. It is performing that function well. Lesson learned.

Adding a Web Controlled Rotator to A3S

Project 7 of 7 for October, 2020 – projects to keep sane during Covid-19 Lockdown

Status: All work is completed.

A new Yaesu G-450ADC rotator was ordered from GigaParts. Still needed are the rotor plate, the cable, and the interface to make it remote controlled. Cable and interface are on order from DXEngineering and HRO. This project has hit a snag. Rotor plate is special order and has a November ship date. It has not even been ordered and by the time it gets here the weather could be too wintry to install it.

Universal Towers saved the day. An order was placed directly with them today and they promised a much earlier delivery date.

“The rest of the story” is this tower is decrepit. It was used 10 years to hold up wireless Internet antennas on a windy hill. It has two blow outs from being overloaded. Even though the blowouts have been repaired the concern now is it might not be able to keep the A3S in the air. Torque is the tower killer when wind makes a beam twist. An overloaded tower can fail from that twisting motion. When this tower is down for the rotor installation a torque arm will be attached in an attempt to reduce the twisting motion.

Remote Controlling The Rotator

All parts have arrived. The Yeasu G-450 rotator is the new DC version which makes absolutely no detectable difference in the operation but it makes lightning protection easier. Relays had to be used on the AC rotator because the AC voltage was too high for the 26vac/31vdc MOV’s on hand. Perfect for the 20 volts DC the new version uses. Modifying the controller for access over the Internet looks like this:

Actually the controller is not modified. A few wires are tacked onto existing terminals inside. Wires are brought out through an existing hole. The controller could be easily restored to original. In the picture above, the green thing at the bottom is the remote interface from RemoteRig.com model RCU-1216:


The interface talks to the RemoteRig 1216H Webswitch and will get mounted inside the controller. A Webswitch already exists at the remote site to provide remote access of the first rotator on the taller tower. That missed getting written up. That’s why this is being written up now. The unit has the capability of two rotators so all that was needed was this interface to the Webswitch. The installation just needs some hookup wire and a solder iron.

There is no brake release button on Yaesu control boxes so a brake release connection is not needed. Only the Pot potentiometer connection and the two motor activation buttons are needed. A data pair and a power pair connect back to the Webswitch.

For this rotator the two jumpers, P5 and P6, are opened up to accomodate the voltage on the Yaesu rotator for direction indication potentiometer. Voltage maxes at 1.3 volts on the pot. Next attach a little Blue Tack or 3M gray stickem to hold the interface in place.

Stick it to the inside of the cabinet and you’re done. It should look something like this:

Coming out of an existing hole in the back are two pairs of wires. One is for 12 volts DC. The other is the 1-wire data pair (1-wire really means 1-wire and ground). Next step is to install and test at the site.

Today the rotor plate was mounted and the rotator is mounted to the plate. A short piece of aluminum tubing was cut to go from the rotator to the mast. A hole was drilled for a bolt to keep the mast from twisting and slipping.

The tower was raised a few feet to see if it is too heavy with the rotator. It is noticeably heavier and harder to lift but not impossible. None of the gin components complained. The rotator only weighs 7 pounds and the wire is probably 2 more pounds. Another 9 pounds is apparently not overdoing it. Next the cables will be extended where needed for slack and they will be dressed. The bolt will be installed. The rotator connector will have a waterproof boot installed. The balun will be reworked to provide enough slack for turning the antenna (the balun is near the center of the picture with cable ties holding it to the tower leg). The rotator cable will be run through the cable entrance at the shed and MOV lightning protection will be provided. Inside the shed the controller will be connected to the RemoteRig Webswitch and all will be tested. It will be really nice to be able to turn this beam in the direction of the signals as they change.

Today, the balun was rebuilt by replacing the RG-58 windings with LMR-400. It is still 5 turns through a stack of 4 Mix 52 ferrite toroid cores. It looks like it can handle a lot more power now. Only the common mode current is flowing through the toroid.

Proving the balun is working is a matter of observing the signal pattern on pskreporter. In this case it is a nice flashlight beam shape in Europe indicating the balun is doing it’s job. It’s job is to keep common mode currents from generating stray radiation which distorts the pattern. No pattern distortion, the balun is working.

The rotator mounting is completed and the cables are dressed. Ready to raise the tower.

Back up in the air the rotator turns the beam perfectly with no issues. As for remote control, a relay is being used to switch between the two rotators. The other rotor turns the 203BA 20 meter beam on the big tower. One rotor at a time is accessible over the Internet.

This project is completed.

Amplifier and Inverter

Project 1 of 7 for 2020

This project has been completed. See “1.5 KW Amplifier Off Grid” https://w0qlremotebase.wordpress.com/2020/10/14/1-5-kw-amplifier-off-grid/

A new amplifier is on order and installation parts are arriving. The good ole SG-500 gave up the ghost and besides it didn’t have 6 meters. Good excuse to look around for a new amp. Deciding on which amplifier to chose was a tough decision because many fabulous new amps are on the market today with 6 meters and great new features. The decision was made easier because one amp looks like it was designed from the ground up to integrate with the Flex. It is the 4O3A PowerGenius XL, or just PGXL for short. Good experience with another 4O3A product (the Antenna Genius) is a strong selling point. A PGXL is on order from Flex.

Going from the 500 watt SG-500 to the 1500 watt PGXL requires some power improvements. A new amp cannot be run on 12 volts. It was decided to add a separate set of batteries, an inverter, and to go to 24 volts and stay off-grid. The existing 12 volt off grid solar system will stay in place untouched for use by the existing 12 volt equipment. The hope was to go all the way to 48 volts for efficiency but no solar controller could be located that would provide low temperature foldback. Foldback is important because it reduces charge current when the temperature is below freezing. The Morningstar ProStar 30 currently in use on the 12 volt system does provide foldback and it works for either 12 volts or 24 volts. Thus the decision was made to run at 24 volts to make sure the batteries are protected in the winter. It takes big wire to carry the 200 amp current needed. The inverter manufacturer recommends this 1/0 cable to run between the batteries and the inverter.

Deciding on an inverter was also a tough decision because there are a lot of fabulous looking inverters on the market. Hybrid means the inverter is combined with a solar controller (charger) in one cabinet. The new so-called hybrid inverters would simplify things but none could be found with temperature foldback. Two more must-have features limited the choice greatly. First, the inverter must have FCC Part 15 Class B certification or equivalent. Inverters are notorius for generating RFI and presumably an FCC certification will fix that. No China inverters have certification. The other must-have is pure sine wave output. That’s pretty easy to find. Output voltage is also important because the amp can’t run full output power on 120 vac. It must have “220”. That number is in quotes because it is has become a generic term to describe 230 volts in some countries and 240 volts in the United States. Since the amp was made in Europe it will be quite happy with 230 volts. There is no neutral wire on European circuits. No 120 volt appliances can be run from this inverter. The inverter that was decided upon and is on order is the Victron Phoenix Inverter Smart 3000.

. A week later the inverter has arrived and is unboxed, looking like a work of art. It is 24 volts in and 230 volts 3000 watts out.

Victron recommends using 1/0 wire for this model between the battery and the inverter. That is the largest wire ever used at W0QL and a new crimper had to be obtained along with terminal lugs for 1/0.

A closeup look at the crimps with heat shrink tubing installed.

Mounting the inverter was a piece of cake.

Lugs are easy to reach.

The very first cable attached was the green wire ground. This wire runs directly to the copper ground bar which is bonded to the ground ring around the shed.

The 1/0 cables were bolted and strapped in. One more stage is finished and ready for the next equipment to arrive: the batteries, the BMS, and the AC power parts. A 250 amp fuse is midway down the battery cables. At the lower right is the terminal block for the cables from the BMS. One thought is to replace the terminal block with current shunt from another Victron Coulomb counter battery monitor. No decision has been made. The batteries will go in that big bare spot on the floor.

Current status: Amplifier shipped last week, has arrived in UPS facility in Denver, awaiting delivery Monday or Tuesday, September 22, 2020. Batteries are still off shore or in Customs.

Amplifier arrived but no place to plug it in yet. Batteries have still not arrived in the States.

A decision was made today to temporarily borrow half of the cells currently in use for the 12 volt system and rewire them for 24 volts until the permanent batteries come in. On the floor is the borrowed temporary 24 volt battery pack. This pack provides 100 AH which is enough for testing at moderate RF power levels. It is being charged by four 12 volt solar panels connected in series-parallel to provide 24 volts nominal. BMS? A 24 volt 8s 100 Amp BMS was found in the junk box and put to work.

With this pack the inverter powers up perfectly and provides it’s default voltage of 230 volts AC.

The amplifier is on site for testing but not in it’s permanent place yet.

It is rather massive and needs a little more space cleared out before it can be completed. Initial tests are amazing. Antenna and feed from the transceiver are the only connections to the Flex 6600. All control, CAT, PTT, and ALC signals are over the LAN. Upon firing it up the amp found the radio automatically. Like people say, the operation is so slick it just acts like a bigger front end for the radio. No tweaking or peaking needed nor bandchanging. The amp follows the band on the radio transparently. The operation is just amazing. Testing with the temporary battery the amp was given 10 watts RF input. Output was 350 watts. The inverter reported a drain of 1000 watts. With no way of measuring the battery drain it looks like another Coulomb counter is in the future. The inverter can display instantaneous battery load but not the capacity remaining. This is a learning experience.

This project has been completed. See “1.5 KW Amplifier Off Grid” https://w0qlremotebase.wordpress.com/2020/10/14/1-5-kw-amplifier-off-grid/

Flexradio 6600: Notes On SO2R Failure

Subtitle is “SO2R and FT8 crashes system”

The way it is envisioned to work:

Open two slices on the 6600 and two instances of WSJT-X. Configure the settings so one slice goes to one instance and the other slice goes to the other instance. In operation one would click the Enable Tx button to establish a qso on one of the WSJT-X instances. A user could also click the Enable Tx button on the other instance to establish a second qso. Both instances would take turns in using the transmitter and the two qso’s would be completed in due time.

How it actually works:

Clicking on Enable Tx on the first instance causes a third slice to open for no reason and no transmission is made. Clicking the Enable Tx again to stop the transmission leaves the third slice still open. Clicking Enable Tx again closes the third slice and starts a normal transmission. In other words instead of initiating a normal qso the Enable Tx button toggles a third receiver slice for no reason. This behavior is repeatable each time. The second instance of WSJT-X doesn’t seem to have any issues, only the first instance.

Progress: A workaround was tested using the MultiFlex feature and a second computer. Setting up a second computer with Smartlink and WSJT-X then dialling into the same Flex 6600 works fine. Only problem is it requires a second pc and it requires a second Internet connection and bandwidth usage. And it’s not the way the Flex is supposed to work.

Idea for next troubleshooting effort: In WSJT-X configuration make the radio type Kenwood TS2000 instead of Flex6xxx. This is a suggestion obtained from a YouTube video.

Using Kenwood is not a solution because that radio type does not have a TCP option. No way to connect to the FlexRadio.

Followup June 21, 2020: It’s working now, full SO2R mode, by connecting to the 6600 with two separate computers. This is using a feature called MultiFlex where two connections can be made to the 6600 simultaneously. The single transmitter is first come first serve but as soon as the first connection is done with a qso the second connection has the transmitter available for a qso. Using two computers and the accompanying bandwidth is not what was hoped for but this satisfies the SO2R definition. Now for a contest to test it under stress. Meanwhile the hunt for a single computer solution will continue in the background.

Client Side

What does the client side look like?  Here’s a snapshot.


From left to right, the Icom IC-7300 is the local station (nothing to do with the remote base).  It is connected to an antenna consisting of a piece of hookup wire outside the window — a vertical with an automatic tuner at the base and a piece of welded wire fencing for a ground plane.

On top of the IC-7300 is an Intel NUC computer that is used for two functions.   First, it runs applications for the local IC-7300, specifically WSJT-X and JTAlert.   Second,  it provides remote access to the 6 meter station in Strasburg via remote desktop connection.

In the center is the monitor for a remote desktop connection to the main station in Strasburg.  To the right is the second monitor for the same computer.  The computer is another Intel NUC  hidden under the desk in this picture.

Also visible is a Yaesu FT-7800 for vhf and uhf local repeater conversations.

On the wall above is the collection of wall paper decorations.  On the left is the station license, then the DXCC certificate, Honor Roll plaque, ARRL life member plaque, and finally the 5 band DXCC certificate.  A great circle map is partially visible.


Once in a while a little extra help is needed to obtain a contact with a DX station.  That extra help can come in the form of a few more watts.  When a difficult DX contact is completed we call that being deserving, as in, “We are among the deserving” (Where Do We Go Next, Martti Laine, OH2BH).  Here is a photo of the new amp and my silly grin shows a combination of emotions.  Sheepish for adding power to a weak signal mode but thrilled at the same time.


(Actually the emotion is more, “Can I get this damn cell phone to take a selfie”.)

Design contraints of a remote base station off the grid quickly narrow down the choices of linear amplifiers.  The SGC  SG-500 was the obvious choice because it changes bands automatically using rf sensing, runs the finals at 12 volts, and has a remote on/off switch ability.  Luck was with us when we found this pristine SG-500 for a good price at QRZ Swapmeet.

The amp can draw up to 90 amps.  We rearranged the battery banks to dedicate one bank to the amp.  Everything else is on the other bank. Testing showed up no problems except a tired SO239 coax connector.  We escaped replacing that by using a PL259 with a slightly longer center pin so it would push against the solder cup at the back.  Deferred maintainance.  With 10 watts input the output is 150 watts with no complaints from anything else in the station.  On to the first on-air test.

First QSO

Wow, amazing, superlatives are not enough.  Noticing a big pileup for a station with the call 3D0AY (Swaziland) on 20 meters, I found a clear frequency and clicked the transmit button.  Seven others were calling at the same time.  With only four calls, on the 4th transmission he came back to me!  Here is the proof.

IMG_0116 (1)

As soon as Swaziland anwered my call another station jumped on our frequency.   I found another clear spot and tried to complete the qso with Swaziland.   He came back again and we completed the contact.  Another station immediately jumped on the new frequency.  A difficult qso but my station joined the “deserving”, thanks to the new amp.  I’m hooked.  I’ll be using this whenever a pileup is tough.

Unfortunately there has been no second qso using the amp.  It seems to be malfunctioning.  It began immediately switching off and the high vswr warning light came on.  Changing to manual PTT got rid of the vswr alarm but no rf comes out of the amp.  It draws a large amount of current but where are those amps going?  It will probably have to go back to SGC for a look.  For the time being we are not using an amplifier.

Update:  I tried the amp using a different radio and it works perfectly. Go figure.



Thoughts on Grounding

Ground the main strike at the tower base.  Worry about protecting your equipment (and people) from what’s left over.

My tower and my equipment shack are 100 feet apart.  Bonding the two would be fruitless because of the inductance of the bonding conductor.   So don’t bond when the two are that far apart.  Ground the tower.   Ground the shed.  Worry the most about protecting the equipment in the shed.

Accomplish the first part by putting a ufer ground* in the concrete base and spacing ground rods around the tower, all bonded in a wagon wheel ring.  That should divert just about any lightning strike.  Do not bond to the equipment shed when it’s 100 feet away.

At the shed install spaced ground rods and bond them in a wagon wheel ring.  Install protection on all cables at their entry point, coax, Internet, power, rotator, etc. and bond together.



*The Ufer Ground is an electrical earth grounding method developed during World War II. It uses a concrete-encased electrode to improve grounding in dry areas. The technique is used in construction of concrete foundations.   –Wikipedia


The principle of the Ufer ground is simple, it is very effective and inexpensive to install during new construction. The Ufer ground takes good advantage of concrete’s properties. Concrete absorbs moisture quickly and loses moisture very slowly. The mineral properties of concrete (lime and others) and their inherent pH means concrete has a supply of ions and free electrons to conduct current. The soil around concrete becomes “doped” by the concrete, as a result, the pH of the soil rises and reduces what would normally be 1000 ohm soil conditions (hard to get a good ground). The moisture present, (concrete gives up moisture very slowly), in combination with the “doped” soil, make a good conductor for electrical energy or lightning currents.   —psihq.com

Cable entrance cabinet with single point ground plate and protectors.  All cables pass through this box before entering the shed in an attempt to stop all strike current from going inside.  The copper plate is bonded to a ground rod and eventually a ground ring around the shed with spaced ground rods.


June 28, 2017: John picked up 100 feet of No. 2 Solid Copper today to serve as the ground ring.  Yay.


Transmitter Failure at Elizabeth

Bulletin:  Transmitter at the Elizabeth site is not putting out any power.  Receiver is working and all other functions seem to be normal.  Transceiver is drawing about one-third normal current when placed in transmit mode.

This symptom appeared last night immediately after a thunderstorm.  We suspect lightning damage, of course.  A site visit is planned for today to swap out the transceiver and Remote Rig and to make a visual inspection.

Update:  Kenwood USA gave me by email a test to run which I had already run and it failed.  Kenwood said to send it in which I will do asap.  Meanwhile a used replacement TS-480 has been purchased and should be here Thursday.  Although this seemed to be a surge failure at first no other equipment failed simultaneously.  It may turn out to be heat related as we are currently in mid summer heat in this part of the world.

Update 8/15/2016:  One can of spray paint later the box is now white.  The hope is white will keep the cabinet from overheating in the hot afternoon sun.  Originally the cabinet was supposed to be located in the shadow of the panels.  At construction time we were one T-post short.  Moving the cabinet to the side solved that issue but left it in the sun in the late afternoon.  A bad scenario.  The best fix is to move it to where it was designed to go in the fitst place.

We have the new replacement TS-480 radio installed and we’re back on the air at last from the Elizabeth, Colorado remote base station.  Hooray.


“End of Story” update – September 29, 2016 –  Kenwood says the transceiver needs a new final RF board at a cost of $350.  Considering these radios are only $600 used, I decided to not fix it and repurpose the front panel for a test unit.  When it comes back from Kenwood the base unit will go on ebay or qrz for parts.

A few months later Ham Repair in Dallas was discovered and the repair only cost $165.  A much better solution than Kenwood technical support.  http://www.hamrepair.com/

Meanwhile I installed a fan in the white cabinet along with a thermostat to turn it on when the temp is above 84 degrees F.   Better late than never.


With lightning season in high swing lightning protection is an important topic.  At the radio cabinet we are following the generally accepted practice of a single point ground system. This means we connect all devices to a single point so that at the moment of an “event”  potentials will rise and fall simultaneously for all devices. Potential differences are eliminated and therefore damage is eliminated.  For the single point we have chosen the ground rod at the equipment cabinet.  An 8 foot ground rod has been driven and all devices in the cabinet are connected to it.  Below, the ground rod can be seen as well as various wires connected to it making it the single point of ground. The frame of the solar panels is also connected to the ground rod. (Bonding the frame is not in compliance with NEC 2014.  See “Section 690.47(D)” for details. We feel we might be ok here because we are not connected to the grid).

2016-04-09 14.02.07

An appropriate surge protector is installed where each cable enters the cabinet and the protector is in turn connected to the ground rod.  This is to provide a path to ground through the protector and not through the equipment.

The antennas are located 100 feet away from the cabinet (to solve interference issues ).  If the two were closer the antennas and associated devices should be bonded to the same ground rod using 2″ copper strap.  No. 6 copper ground wire would likely “fuse” and melt upon a direct hit.  We could have driven a ground rod at the base of the antenna.  If the antenna was closer to the equipment that would create a dreaded ground loop.  At 100 feet separation it’s probably far enough not to hurt anything. The function of the ground rod is performed by the radial ground screen acting as an electrode.

Ward Silver, N0AX, says in an article in September, 2015 QST, Grounding and Bonding Systems, p69, “…if the tower is not located close to the house and it’s bonded earth connections..the radial ground screen can help spread out the charge.”

We’re going on the principal that we have two systems not bonded together except by the coax cables and the cable will “fuse”  (and become an open circuit) upon a direct strike. We also expect the long cables will provide enough inductive reactance before they fuse to isolate the two systems.  I believe NEC refers to this concept as “impedance” grounding. The two systems are defined as follows.  One is the cabinet and a ground rod for a single point of ground.   The other is the antenna and it’s radial screen acting as an electrode.  There is no ground rod at the antenna.  We expect the system that gets hit to dissipate 90 per cent of the charge.  We expect the other system  to suppress the other 10 per cent without damage. We further expect the cables in between to suppress a considerable portion of the charge before fusing.

Another important feature not to be overlooked is the shape of the antenna.  A pointy vertical tends to put up feelers which lightning step leaders search for as they come down out of a cloud.  A flat surface tends not to put up feelers.  Our inverted vee flat top at the top of the vertical antenna provides that flat surface and reduces feelers.

Laughable inconsistencies.  On the other hand the 20 meter EF-20 half wave vertical has everything wrong about lightning protection.  It is pointy, likely putting up feelers during a thunderstorm.  It has no ground rod nor ground screen.  It is a culprit waiting to cause lightning problems.  On the positive side it is a thin wire which will fuse quickly and it has only a coax running back to the equipment and it runs though a Polyphaser surge protector at the entrace to the equipment cabinet.  Even though it’s a thin wire it can put up feelers and attract a lightning bolt. Once the EF-20 is vaporized the charge will need to find an alternate path to ground with an unhappy outcome. (I was checking the antenna one day as a thunderstorm approached, maybe 5 miles away.   The coax was biting me something fierce.  I hope those Polyphasers do their job.)

Another laughable inconsistency is the fact that the cabinet is not conductive.  It is fiberglass.  At the new remote base the cabinet will be made of stainless steel. Metal could prevent the charge from bypassing the protectors better than fiberglass. We just do the best we can given what we have.