I recently received back my Expert 1.3K-FA linear back from its holiday in Italy. I noticed some months ago that it would sometimes fail to start and require repeated presses of the power button. After a short holiday in Italy, the manufacturer replaced two relays, and I thought WPX RTTY was a good baptism of fire.
Apparently, these are the faulty items, now replaced under warranty. Linear was working flawlessly and allowed me to complete 218 QSO on 7 MHz.
Using the doublet antenna, I wasn’t able to find much DX, but using the club call MX0SNB did provide some interest on the bands.
Even after some prolonged CQ runs the liner was able to deliver 400w RTTY and remained under 50 C
Interesting to see the VSWR at 1.01 and the temperature at 50C.
Bands seemed busy, I opted to only operate on 7 MHz and so conditions provided mostly contacts to EU. I was able to work into the USA, and I did hear China and Indonesia although was unable to work them.
I put together this map showing QSO mostly over the EU.
I managed to work 45 countries, with the best DX being Peru.
Always nice to see the bands busy, and RTTY has never been so popular.
Let’s start with the name, MMDVM (Multi-Mode Digital Voice Modem) with HAT(Hardware Attached on Top)
The HAT has been designed by Flo DF2ET and Mathis DB9MAT and is compatible with the Raspberry PI or PI W Zero. The board will support MMDVM so that’s DSTAR, DMR, P25 and Fusion using the excellent software by Jonathan G4KLX.
The Raspberry Pi zero W (WiFi)
The board that brings together the UHF module, the STM32F103 CPU that is plugged directly onto the smallest Raspberry Pi, the Pi Zero W. The hotspot can be configured on the dashboard to operate on any or all digital modes and to operate on the UHF frequency of your choice.
I have mine setup on to provide a digital access point on 435 MHz, but your allocated frequency will vary by local usage and regulations. It has around 10mW of power, so ample to provide access all around the house using a handy.
A close look at the MMDVM_HS Pi Hat
The screen can be anything of your choice, I opted for a small OLED screen but in hindsight, it should have been a little bigger as one’s eyes get older!
If you have spent time listening to HF you may have noticed the distinctive sound of HF Fax, something I thought had disappeared 20 years ago.
FAX seems like a very old technology now, although before the days of email the FAX machine was the only way to send near real-time images between people. HF Fax uses the same principle, but instead of squirting the tones down a phone line we modulate them onto an HF carrier.
It’s still very slow, but if you are on a yacht in the middle of the Atlantic its a very low-cost alternative to using a Sat phone and data. The charts are still transmitted from a number of locations around the world, using very high power 5 to 20 KW HF stations, so reception is easy even with a modest antenna.
You can use one of the online KiwiSDR to display the maps, this allows you to select the FAX overlay option in the top right-hand box, then region and download the image.
FLdigi can also be used to display the images on your screen. Using the schedule of transmissions tune your HF radio to 4608.1 KHz USB and set up FLdigi to your sound card. You will need to set the OP Mode to WEFAX then WEFAX-IOC576,
If you miss the start of a transmission don’t worry, just leave the receiver and program running and it will sync and start decoding on the next image. The transmission schedule is quite extensive, so you never have to wait long to resolve an image.
Here is an example from 4608 KHz decoded at 12:58 Hrs on 1/1/18
The transmitted images change based on a schedule, one typical example is included below.
70 MHz has become increasingly popular since Icom added it to some of their new transceivers. Since owning an Icom 7100 and enjoying the UKAC and portable events I decided to make a beam for the band.
In my case, I had some lengths of 8mm and 10mm tube and a 25mm box for the boom. The website allows you the flexibility to specify the desired frequency and then select the required gain or boom length. Thankfully the design can be created in both metric and imperial measurements, you just specify the sizes in the design.
The current design is an antenna for 70.2 MHz. It has 1 Reflector, 1 Driven, and 4 Director Elements. Estimated Gain is 8.917 dBd.
This is specified at the time of the design, it is interesting to see the design with and without insulated elements. Insulating the elements from the boom has the effect of shortening them slightly, but why not have a play with the calculator and see the difference. The insulators I used were 4mm ABS plastic, cut into strips but you can use anything to hand.
Often the most difficult parts to complete, as it requires a split and insulation from the boom.
1/ Place a small plastic tube inside both parts of the driven element, thus making them rigid and then mounting this to the plastic insulator on the boom.
2/ Fix the driven element directly to the plastic insulator using 2 plastic clamps on each section. This should provide enough support to stop the element sagging or twisting.
Black Plastic Nylon P Clips Mounting Cables Tubes Pipe Brake Motorcycle Car. These can be used to fix the elements to the insulator, they are available in various sizes. The clips allow the elements to be removed by simply pushing/pulling the element into the clip, and are therefore ideal for portable use.
Something more robust would be needed for a permanent solution.
Stauff clamps can be sourced online. These are more expensive than other options, but ideal for a permanent antenna build.
VHF dipole centre available from your local rally, eBay or junk box
The antenna is a little quirky, the dip shows a good match at 70.200 and the bandwidth is wide enough to cover the entire 70 MHz band. The dip shown on the RigExpert is a little nonconventional, but it certainly has gain and good F/B ratio from the testing on site.
Following on from the previous post, WSPR reception continues mostly 24×7 with a focus on MF. As previously described the setup has been operating for a couple of weeks now, and its a good time to review the WSPR spots.
Best DX Spotted
52 unique calls received, you can download the complete list online.
WSPR reception 24×7 has always been something I have wanted to try. The problem is trying to find a transceiver, computer, antenna combination that will allow this with minimum fuss.
472 KHz Reception
You won’t need a very high spec computer, but if you are leaving it on 24×7 low noise and power consumption will be high on the priority list. A laptop is one option, although they often have fans and may not be noise free, so you may want to consider one of the new breeds of “minicomputer”. Low power consumption, and low noise with many running on 12v. I opted for a second-hand minicomputer, silent running and powered from 12v. It uses the Intel Celeron J1900 with 4 cores and I added a 128G SSD so it boots in 3 to 5 seconds. These are good value and should provide a reliable machine, with a very small desktop footprint.
If you looking to cover multiple bands then you need a broadband receive antenna and this typically doesn’t work well on a simple unmatched G5RV or doublet antenna. I completed some receiving tests using my doublet and a Wellbrook and found the loop outperformed the wire antenna significantly below 5 MHz. You can read more about receiving loop antenna on this page. George M1GEO has provided a very interesting article and instructions on how to build a low-cost Wellgood loop on this page. The Wellbrook loop I use seems especially good at 136 and 472 KHz, providing some interesting spots on these bands. The antenna is shared with my online SDR providing connectivity to the ELAD and Kiwi via a 2 port antenna splitter.
I use the ELAD SDR, as its very low power consumption, and I can CAT control the band changes to suit the time of day. The radio is connected via USB to the PC running Joe Taylor WSJT-X program.
The transceiver draws around 500 mA on receive and the Mini PC around 600mA at 12V. I have used a 12v SMPS designed as a computer power supply, its rated at 5A and runs cold.
In the last 24 Hrs
Receiver antenna and band changes biased towards MF and LF