Motorhome Mobile operation on HF

A homebrew vertical for HF WSPR ‘Mobileers’

Since retiring to NZ in 2013 we have been travelling the country in our motorhome. Its an ex-rental 6 berth Kia Dreamtime Deluxe. Plenty of space for Maria and me. We both have our hobbies and the van is sufficiently spacious to allow us to occupy different parts of the living space without getting in each others way. Maria has the ‘lounge’ area with its picture window, and I have the 4 seater breakfast table. This doubles as my operating desk and construction bench. In the last 3 years this has worked very well.

When we first went mobile I was determined that I would have a radio station that was compact and easy to use. I had an Elecraft K2-100 and a QRP rig, the KX3. I have since acquired the latest Icom rig, the 7300, which is mentioned elsewhere on this site. I spent considerable time ( months ) scouring Ebay and Trademe looking for the LDG remote ATU, the RT-11. I had owned one of these back in the UK and never had any issues with it. I disposed of it when I purchased a rig that had an auto ATU built in. That was a mistake ! Not many integral tuners can handle such a wide mismatch as an external tuner can. So when we arrived in NZ I had no auto ATU. My patience was rewarded when I eventually found what I was looking for in USA. Rather than ‘peck’ at the bidding, I immediately bid what I was willing to pay. I think that was equivalent to £80GBP. The bidding didn’t get that far and I got what I considered to be a bargain. Exactly what I wanted for less than I was willing to pay. The total cost including shipping amounted to £78GBP if I recall correctly. The plan was to install the ATU inside a rear locker of the van and control it remotely using a homebrew button box. In the meantime ……..

Home is where you park it.

One useful item that I brought with me from UK was a 8m fishing pole. I had planned to repurpose this as my mobile vertical antenna. After some trial and error I eventually mounted some 40mm waste pipe to the rear ladder using heavy duty cable tie wraps. I removed the bottom section of the pole as it was too large to fit inside the waste pipe. I also removed the top section as it was too thin to support the antenna wire without bending. The wire is silver plated ( I think ) and white Teflon coated. Courtesy of Westlake if I remember. The overall length is 35ft. No particular ‘magic’ length, just the longest piece of wire that fitted the installation. A few turns of insulating tape near the top and bottom of the outer section of the pole ensured a snug fit inside the wastepipe. The pipe has a stainless steel cross bolt near the bottom, to stop the pole falling straight thro, and its overall length is about 50mm shorter than the fishing pole. This is so that when the pole is collapsed inside the pipe, at least a small part of it is accessible so that it can be easily extended.  The wire is loosly spiralled around the pole, down to the top of the white pipe, where it is secured with yet more insulating tape. The loose end then drapes down the back of the van and is routed into the rear locker. Here I had a balun mounted inside a plastic sandwich box. The coax ran alongside the van, and was routed thro a window to the radio. Erecting the antenna, deploying the counterpoise and running the coax to the radio took a few minutes, but was a real pain in wet weather. The auto ATU inside the rig would match this antenna setup on 40 and 15 with quite a low VSWR. However some of the other bands of interest were not so good. So about 14 months later ……..
I read some really complimentary revues of the Icom 7300, and subsequently ordered one. Despite being told by Icom NZ that the radio was in stock, I had to wait a month before it arrived. I assume they meant it was in stock in Japan, they simply neglected to mention that detail. Nevertheless when it arrived I was very impressed with the whole thing. My only minor criticism is the lack of a bandswitch. You have to use the touchscreen. 

I soon dicovered that the 7300 had an auto ATU control port and to my delight, that it was compatible with the LDG tuner,  which was still languishing in a storage box. Other than initially testing it I had never used it. I ordered a suitable Molex connector from a local on-line trader that would fit the ATU port on the 7300. The next thing to do was install a run of coax and some 4 way screened cable from inside the van to the back locker. This turned out to be considerably more difficult than I had imagined. I purchased the cables at a local outlet and was disappointed to find that the screening of the coax was nothing like as substantial as previous examples of RG-58 that I have used, and still have some short lengths of. Satisfied that the distance from the radio to the ATU was quite short I decided to use what I had rather than spend more time search for something better. Not a lot of choices in Northland NZ. Trying to purchase some flexible conduit was another problem. It was available from a number of places, but at a price that I considered too expensive. I eventually bought a couple of 3m lengths of 20mm water pipe. Being in a campsite with a hardstanding ( Waitangi ) and in dry weather, the day arrived when everything was ready for the installation.  I squirmed under the van on my back and checked out the cable routing only to discover that I would have to cross a chassis member to get to the rear compartment, mainly due to having to avoid the double rear wheels. After much indecision and not a small amount of bad language, I fitted the water pipe along the chassis member as best I could, whilst avoiding the shock absorber, the wheels and various other bits of automotive hardware. This took far longer than I had planned on spending on the whole project.  A few heavy duty cable tie wraps eventually held it in place. The cables would be exposed for about a meter at either end but at least the majority of the run was protected.  

After very carefully measuring the floor area below the seating storage compartment inside the van, I drilled 2 holes of 8mm diam thro to the underside of the van. Similarly 2 holes were drilled into the sidewall of the rear storage locker. Feeding the cables down thro the floor then thro the length of pipe and into the locker was easier than I expected and was completed in a very short time. I tied both cable ends together inside the van end and pulled all the rest thro to the back of the van, out of the locker and then back inside the van thro a window. This allowed me to use my soldering iron to fit the PL259 to the coax and the DB9 to the multicore. I then pulled the excess cable back into the van, at the radio end, until there was about 150mm showing at the antenna end. This would be sufficient to reach the RT-11. Inside the van I dressed the cables along the inside of the seating compartment and then thro a gap in the seating hardware to a narrow shelf on the sidewall underneath the breakfast table. More cable ties ! On the shelf I mounted a small ( 100mm x 50mm ) plastic box and the cables ended there. On the lid of the box there are BNC, DB9, Red & Black 30A power terminals and 3A aux power spring terminals. The power terminals are connected directly to the house batteries. 2 x 85Ah deep cycle lead acid types. The spring terminals are in parallel.

LDG RT-11 inside the storage locker.

 The RT-11 is mounted inside the locker ( which is on the right hand side just forward of the light cluster ) and the antenna is connected directly to a terminal post on the ATU. Before installing the ATU, I constructed a heavy duty 4:1 balun and fitted it inside the ATU case along with some terminal posts for antenna and ground connections. See this easy design at               I used a T-130-2 toroid.

4:1 balun

The ground terminal connected to A, is also bonded to the metalwork of the chassis by a very short braided cable. The antenna and counterpoise wires are attached to the balanced terminals. I assume the antenna appears to be an ‘L’ shaped dipole as far as the balun is concerned. The ground counterpoise consists of 2 wires measuring 35ft and 16ft. These are 1/4 wavelengths on 40m and 20m. When travelling, the antenna is collapsed, of course, and the antenna wire is hung in loops around the top of the white pipe. The waste pipe makes the antenna almost ‘invisible’ when on the move. The counterpoise wires are stored in the back locker.
Does it all work ? Oh yes. VSWR was checked with the antenna analyser built into the Icom 7300. On all bands from 40m to 6m the highest SWR was no worse than 1.5:1. The antenna is not suitable for  80m and no attemp has been made to make it so. My best DX on 30m WSPR, is Portugal, using 1W ( the lowest power setting on the 7300 ). From my location in NZ that is just 60km short of 20,000km. Can’t get much further than that on the planet. 

Milliwatt meter for WSPR

Having the need to measure milliwatt powers from my WSPR transceiver, I decided to build a simple measurement device that would indicate power up to 5W. The QRP milestone. I have a couple of SWR / Power meters, but nothing sensitive enough for such low levels of power. A search around the web produced many projects, almost all based on the same circuit.

This is my take on a fairly standard circuit. Note the diode has a forward voltage of only .4v. Max voltage is 30. So the device should handle up to 15W. You will need to beef up the load resistors if you build it for this higher power level. Diodes such as the ubiquitous 1N4148 can have voltage drops up to 1v, according to the datasheet. This will reduce sensitivity and accuracy at really low power levels.

Calibration can be done by applying a known 5W from a transceiver, Elecraft KX3 as I used for example, and adjusting the pot for the correct reading on the meter. My meter was salvaged from an old SWR bridge, so the scale was conveniently  marked.


Alternatively apply 15.82 volts to the point marked on the circuit and adjust the pot as above. The more accurate the calibrating voltage is, the more accurate your meter will be. The power reading is equivalent to (v*v)/R. Where R is usually 50R.

I scored a few pads on a piece of copper clad PCB with a sharp blade, and soldered the parts onto that, keeping all leads as short as possible. The electrolytic 4.7uF across the meter, helps to damp the movement may not be needed and is not shown on the schematic.

This version has 2 pots selectable by a switch ( not shown ) enabling 1W or 5W FSD as required.

Of course it should be installed in a shielded enclosure of some sort. This 50c tea caddy was an ideal size. I didn’t realise how battered it looked until I reviewed this pic !

Icom 7300 and WSPR

The new SDR technology from Icom is a winner in my book. Well in my blog anyway.

Just had it for a week or 2 and I am very pleased with it. Of course radio preferences are very subjective. The only thing I miss here is a bandswitch. You have to touch the main digits on the display. This pops up a band pad and you touch the band you want. Not intuitive, at least not to me. The memories are useful of course, as is the MPAD key which can store your 5 favourite frequencies, and allows you to tune from them.

Setting up the radio for WSPR took me a few hours simply due to lack of information. This is what I ended up with when trying WSPR ON 30m. Anything not listed is left as default. A standard ‘A to B’ USB cable was used. You need to fool your software by telling it you are using IC-7100.

Mode. USB-D


ACC/USB Output Select.  AF

ACC/USB AF Output Level. 50%

USB MOD Level.  40%


CI-V Baud Rate.  9600.  The same as in WSPR – X or set to Auto

CI-V Address.  88h.        This emulates the IC-7100.

CI-V Transceive.   ON

CI-V Output (for ANT ).    ON

CI-V USB Port.   UnLink from [REMOTE]

CI-V USB Echo Back.  On

USB Serial Function.   CI-V

USB SEND and Keying OFF.

The next images show my WSPR setup.

The PC is my MS Surface Pro 4. It connects to the 7300 via the USB port. After setting all the parameters on the rig and in WSPR-X , it pays to switch off both the PC and the rig, then restart. I have no idea why this is effective, but it is. Don’t forget to adjust the speaker volume, this sets the transmit audio level. 

So far, from my remote location at the southern end of Ninety Mile Beach, on the North Island of New Zealand, I have neither received or spotted any other stations. Current transmit power is 5W, and I have heard of miracles happening with less than 1/10 of that power. I have received reports from far afield with a couple of 100mW from my QRP Labs Ultimate 3s, so I think its just a matter of time and propogation conditions.

Evolution. Homebrew SSB transceiver

The basic SSB transmitter wasn’t too difficult. Up to the 5mW level anyway. Trying to get from there to the 1 or 2 Watts level caused considerable grief. There are lots of push / pull circuits on the internet to give guidelines for construction. I found a circuit using a pair of 2N3866’s. Since I had a handful of these in stock I decided to use this circuit, driven by an NE46134. The same transistor used in the Elecraft K3 front end. This produces plenty of drive for the push / pull stage. At least a couple of volts of RF. 

After the unexpected demise of a number of 2N3866’s I suspected that the output transformer turns ratio probably wasn’t correct. I tried optimizing the turns ratio, but only succeeded in blowing further pairs of transistors. I eventually concluded that the transistors were not up to spec. I had bought a quantity, from an eBay vendor based in China, at a bargain price a couple of years ago. A quick look around ebay revealed lots of negative feedback issues concerning fake parts. Once bitten ….. 

I modified the circuit to take some VN1210 FET,s, that I also had a quantity of. Without any changes other than to the bias circuit, this circuit worked first time. By mis-setting the bias, the output pair consumed in excess of 750mA at one point during testing. The solder joints melted. But the devices survived the experience. These transistors are in a TO39 plastic case with a small metal tab that is connected to the drain pin. Not easy to cool due to the shape. After some further fruitless heatsink experiments I shelved the whole transmit idea for the time being.

I arrived back home on 16th Sept. Maria returned from her UK trip on 19th. Over that weekend a search of my gear in my storage shed revealed an old Codan 7727. This has a solid state 100W linear PA module that only needs a few mW of drive, and it has ALC on the PCB. I have pulled this module, and intend to modify the output transformer in order to reduce the output power. 

(Vcc^2/2*Pout) gives the collector impedance. At 13.5v and 65 Watts the turns ratio will be very close to 6:1. Currently the windings are 4:1 so I will need to remove the existing turns and replace with 6 turns. According to theory this should work. I hope it will reduce the heatsink requirements. The PCB is currently mounted on a heavy duty ( 10mm thick ) angle bracket that will allow me to mount it vertically down one side, on the inside, of the transceiver case. Adding a heatsink would not be impossible, but it will have to be cut to fit.

Constructing the QRP Labs Ultimate3S with ZL4SAE. QRSS, WSPR, CW, HELL.

The WSPR Transmitter is multimode.
The Ultimate3S is a versatile WSPR, CW, QRSS beacon Transmitter that can transmit messages on up to 6 bands. The basic kit is single band. A clever mod enables up to 11 bands to be used.

Along with a few other popular mods found here.

  There is also the option of the temperature compensated crystal reference for the SI3151a synth module, rather than the plain vanilla PCB, this can help to reduce frequency drift to 1 part per billion. The synth can produce up to 3 separate frequencies, on 3 separate pins, at the same time. One of these outputs is used to drive the transmitter. Another appears to be sampled by the processor. And the third is used as a ‘park’ frequency when the transmitter is NOT transmitting. I propose to program this frequency to be used as the VFO in my homebrew WSPR receiver. 


Partly built ( modified ) transmitter 30 Mtrs LPF.

My order included a single LPF for 40 Mtrs. I subsequently modified this for 30 Mtrs which appears to be a more popular WPSR band. The mod was simply a turn or 2 less on the toroids and changing 2 capacitors for the next lower value. A table of values is included in the LPF construction details.

   Completed LPF. The missing components are options for other bands.

The transmitter kit.

Some progress has been made. I replaced the cheap 28 way DIL socket with a pair of 14 way turned pin types.

Almost finished. Needs the synth module to be plugged in before testing begins.

Front and left is the single PA transistor, with places for 2 more. The option also exists to run the PA from 12v rather than the default 5v.

Front view. Protective film still attached. Thank goodness, as there was a small spit of flux, which hopefully has not melted thro the film and marked the display. Which is blue incidentally.

The OCXO SI5351A Synthesiser.

The electronics part of the kit is just a handful of parts. Constructing the enclosure for the temperature controlled oven looks a bit more daunting. It all needs to be square. Thankfully the only SMD part is already soldered to the board. Thanks go to QRP Labs ! 

The manual is 45 pages, as opposed to the transmitter kit which is only 15.

These were quite demanding on my patience !

Using a clipboard as a vice helped a bit.

Assembling the synth PCB. Not too difficult.

This is how it looks with the oven chamber attached.

The PCB will eventually fit into the box.

All components are mounted. Set the pot fully counter-clockwise.

The temp adjust pot should be below the access hole on final assembly, of course.

Powered up in DIAGNOSTICS mode, first time. The LCD contrast pot had to be adjusted in order to see the characters.

Completed the assembly, and some basic setup done for testing. Synchronising the kit clock with the PC clock was tedious. You have to do this every time you cycle the power. Fortunately it is the first item in the menu once everything is setup.

Programming other parameters is a bit long winded due to only 2 buttons and a menu system. For example, inside the MESSAGE parameter, the ENTER key is a character that you have to select with the LEFT button in order to save the message. It all works OK. Just read the manual, over and over.

The dummy load is a couple of 100 Ohm resistors in parallel, tack soldered to the output pins of the 30 Mtrs LPF. Idle current was 66mA. I adjusted the FET bias pot to increase this to 75mA. Thats 375mW standing power. At 80% class ‘E’ efficiency, I calculate the ouput power at approx 300mW. I hope thats correct, I’m no expert on class E amplifiers.

YES !! It works !

Receiving on my K2, and my Ultimate3S is being decoded. The receive antenna for the K2 was a 6″ terminal screwdriver. The drift looks good considering the temperature controlled oven is not fully installed or calibrated.


 The 3rd homebrew Direct Conversion receiver. With low pass ( for transmit but left in line for receive ), and bandpass filters.

It worked. But the performance leaves a lot to be desired. I have since built 2 other versions of this and none of them were very good. 

The 2 earlier NE602 / LM386 efforts were hopeleesly inadequate, including the ‘Improved’ version, even with the DDS VFO. Why do so many operators extoll the virtues of this ‘toy’ radio. Its as deaf as a post and as hissy as an Asp. No offence ………

Next step is a superhet. I will base the circuit on the Elecraft K2, itself based on circuits from the classic work, Solid State Design for the Radio Amateur, now updated as Experimental Methods in RF Design. I have both these books, so there is no shortage of research material, or inspiration !

Since I have a couple of 9MHz SSB crystal filters, the receiver will have a 9MHz i/f. The VFO will be the ubiquitous AD9850 DDS, controlled by the equally ubiquitous Arduino. Not exactly a K2 then.

  The receiver comes together, and works rather well. So well in fact, that it is on its way to becoming a transceiver.

  The receiver PCB, built using modular construction, based on Me-Squares and Me-Pads.

  More progress. Wired up for testing. It all worked first time. First station heard on 20mtrs was in France. Not bad DX from New Zealand.