Noise Chase

For a long time there have been multiple signals on this remote base that appear to be digital hash and not legitimate radio signals. On the water fall they look like noise from switching power supplies. Considerable work has been done trying to get these signals chased down. Over the last year each switching power supply has been replaced with a linear supply or the switching power supply has been mounted in a metal box with ferrite chokes on the leads. Since the noise continued, looking elsewhere was necessary. The next suspects are the solar controllers considering they switch power on and off rapidly just like a switching power supply and considering they are about the only devices that haven’t been investigated. Searching the web turned up numerous reports that solar controllers are major contributors of rfi. The controllers used at the remote site* are specifically selected because of their FCC Class B certifications. They aren’t supposed to be generating rfi. That’s why they haven’t been investigated earlier. Today’s testing was very revealing. The controllers are generating tremendous rfi. Later it was discovered the interference occurred only in the mode where the batteries are fully charged. The controllers are in a state of “high voltage disconnect” to avoid overcharging the LifePO4 batteries. When the system is in a charge state there is no interference. Below is a picture of a water fall on 17 meters on a sunny day when the solar system is generating full capacity in a “high voltage disconnect” status.

Obviously those big wide bands of yellow-green are not supposed to be there. They are digital hash caused by something. Their huge signal strength indicates the source is probably local. Next picture is with one of the four controllers turned off. Observe the band on the right and the band in the center have disappeared as the waterfall continues to scroll down. Two bands on the left are still present.

Next, another of the controllers is turned off revealing an amazingly rfi free band. What a stunning difference. Apparently the other two controllers are not generating hash, for some reason yet to be determined.

Toroid chokes on the controller wires should be an easy fix. A hand full of Mix 31 ferrite toroid chokes was placed on the wires that come in and out of the controllers and no noticeable change occurred. Paraphrasing the captain of the boat in the movie Jaws, “We’re going to need a bigger choke”. Upon more Web scouring back home, an article was found that discussed a rarely mentioned bit of information about ferrite chokes.

“Ferrite material choking performance degrades in the presence of strong DC current. For this reason, it is better to pass both DC wires from the solar panels through the same snap on ferrite as this will eliminate the DC bias in the core.”

The chokes had been placed on individual wires in the initial test. About 15 amps of DC was present on those wires. Is this DC current enough to degrade the performance of the chokes? On the next trip to the site, both wires will be placed through the cores and the results will be reported here.

*The controllers used at the remote site are Morningstar PWM ProStar PS-30 and Morningstar MPPT ProStar PS-MPPT-25M.

Chokes On Both Wires Together

Next site visit and the first thing noticed is that different controllers are causing interference than the ones that caused it last time. Here is the first picture upon walking in the door without any testing.

Two lines of digital hash coming down the waterfall are from two of the four controllers, but not the same ones as last time. Next picture is after turning off three controllers and at the 7 second mark placing a choke on both wires of the 4th controller.

The choke clears up a good amount of noise but not nearly all of it. More chokes were added and there was almost no more improvement. Chokes don’t seem to be the answer.

Next topic is why only two controllers at a time cause interference. What is the difference? PWM and MPPT controllers are both contributing equally. It was soon noticed that the interference is coming from the controllers where the batteries are fully charged. When a battery is not fully charged and the controller is working hard there is no interference. When a battery reaches it charged state and the controller stops charging, it starts generating the digital hash. Solutions come to mind both elegant and crude. An elegant solution would be to monitor the modbus data output and watch for the fully charged messages. Use a microcontroller like an Arduino to turnoff the controller. That sounds like a lot of coding and debugging and time spent. Turning to the crude solution, that would be a relay on the solar input cables driven by a voltage sensor on the battery. When the battery reaches full voltage the relay would open and effectively turn off the controller. Call this solution the Rube Goldberg, band-aid, patchwork-quilt solution but voltage sensors and relays are now on order from China. The interference will have to be lived with for a month until the parts arrive.

While waiting for the parts from China an article surfaced that suggested trying 4 turns of both wires through one toroid of mix 31. That was tried and it did not reduce the noise noticeably.

In an act of desperation bypass relays were inserted in the solar panel input leads so each of the panels could be cut off completely if they were causing interference. This is the method referred to above as “Rube Goldberg”. The difference is the relays are controlled remotely from home over the Internet instead of by an Arduino monitoring the modbus or instead of a voltage detector. So far it works perfectly. Case closed. For now.

Update February, 2023. Along came Node Red and big improvements have been made. Go To

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.

Amplifier and Inverter

Project 1 of 7 for 2020

This project has been completed. See “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”


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.



Terrain Profiles

How well our signals will emanate from this new location can be estimated by using software called HFTA (High Frequency Terrain Analysis – from any recent ARRL Antenna Book ) to produce a map of the terrain.  It looks promising because we slope down toward the northeast, which is direction of Europe.  This screen snap is what the terrain looks like as we look to the northeast, or 45 degrees, using a dipole on a 60 foot tower.  Slopes down for 2 miles.  Nice.


Next is a plot of Colorado to Europe using a dipole at 60 feet elevation.  Looks good but could be better.  About 5 dBi gain at the take off angle where most of the Europeans stations come in.   The dipole peaks at 15 degrees, a good all around takeoff angle and very usable but not optimum for Europe.  Four or five degree take off angle is perfect but not likely attainable at this installation.



Raw Farm Land Purchased

This beautiful 40 acre piece of farm land became available this fall, complete with enough space for any antenna, no covenants, nor hoa’s, and perfectly flat and unobstructed. Lucky me, the property is now mine.  Having one’s own land upon which to put a remote base has a much nicer feel than having to borrow from friends.  As gracious as my friends have been it’ll be relaxing to use my own land instead.  This is what the acreage looks like when still a blank sheet of paper.  The mountains are just barely visible in the distance.


A Tuff Shed “barn” is scheduled for delivery tomorrow and then the equipment can begin to be moved in.  Off grid solar power has served us well in Elizabeth and those panels will be moved up here.  A Direct Link internet tower is 7 miles north for Internet access and we should be able to reach that easily.  This acreage is located near Strasburg, Colorado about 25 miles east of Denver in the heart of farm and ranch country.  Access is quick by I-70 and the county roads are paved all the way except for the last mile.  Testing for RF noise showed no S-meter movement off the S-zero level on 20 meters.  The plan is to slowly move the other two remote bases here.  The Tuff Shed will house the remote base equipment and also serve as an operating location on occasion.  It will be big enough to accommodate a camp cot and a sleeping bag.  If a used tower and beam comes on the market that could also be in future plans.   For now the antennas will be verticals.   Lots and lots of verticals.  With lots and lots of radials.

The cost of this land is looked upon not as an expense but as an investment that I can get some ham radio use out of.  Investing in land is almost never a bad thing.   Lucky for us, Colorado is one of the sought after places these days and some say almost any real estate here is a good investment.  We’re fastening our seat belt for the next exciting ride.  Here we go.

November 21, 2016 – Tuff Shed arrives. It doesn’t look so much like a barn as a shed.  From a distance I thought it looks like a yurt until my wife corrected me.  She says yurts are round.  I guess I’ll have to find a better name than “Little Yurt On The Prairie”.


At the closing I asked what the address will be since there was no address on the paper work.  The answer was, “Oh, the County will give you an address when you apply for a driveway permit.”  Reality sets in.   Permits?  We don’t need no stinkin’ permits.  Do we?  Oh, maybe we do.  I’ll put that on my Christmas list.  (February update:  still no permits and still no address )