NDB – LF and CW Adventures

SDR or IC7000 … how do they compare?

I have had a NooElec SDR dongle and upconverter for a while now. Up until the last few days I have just “tested” it and checked out the software but never got too serious about receiving using the SDR for CLEs and NDB hunting.

As mentioned in the previous post, I have exhausted the reach of my current receive systems, gaining only a few new NDB stations (for example) when propagation conditions are exceptional. The SDR looks like a new tool to allow me to expand my listening times.

I like HDSDR and its features suit my current needs. Recording overnight reception for analysis later is what interests me right now. I played around with this last night and found that the reception is similar but possibly not quite as sensitive as my IC-7000 and Spectran using the same antennas. I’ll need more hard data and some experimentation to be convinced that is true.

The recording issue leaves me with a problem … I use a laptop for the shack computer as I can run on battery power to eliminate charger noise while I listen. Recording would only be available for as long as the battery lasted which is under 2 hours. The storage required for 1 hour of recording at the second lowest bandwidth is about 6.7 GB and that is problem #2 … I have only 28 GB free on the laptop drive (3 hours or so without crashing the computer).

Potential solutions include re-building one of my desktop computers and stocking it with some TB drives (a serious undertaking) or adding external drive capacity and power supply filtering to the laptop.

I’ll start by testing the external drive setup with my existing equipment to see if it is worth an investment. I worry about using a USB 1 connection for data transfer (older laptop), this may become an issue so I need to test this further.

PS: I also looked at KiwiSDR as well. I live in a remote place and it would be interesting to run a listening station!

UPDATE:

After a few days of recording and comparing levels on all antennas I have concluded that the differences in S/N and signal level is smaller than I can measure. Each antenna has a different “best frequency range” so I must keep that in mind for future reference!

The Beverage Project

Having basically exhausted my receive capabilities on the NDB and 630m band with the inverted L antenna (I still get a few new signals each month) , I went looking for an antenna that would push my listening limits. I have a lot of acreage handy so I thought about beverage antennas.

There are many good articles (and some questionable ones) on beverages. I purchased ON4UN’s Low-Band DXing and started there. KW2P’s Blog has some information on coax beverages and W8JI’s beverage page is packed with advice.

After much research and many hours with azimuth maps, auroral oval maps and design calculators I have settled on a plan for some 3 meter (10′) high 2-wire beverages in the bog near my house. You can walk in the bog with boots on and there is little standing water. I hope the ground resistance is not too low for a beverage to work effectively.

The image below (north is up) shows the complete layout. The build will come in phases so as not to work myself too hard!

The sparsely treed area is the bog. Power lines are 30 meters (100′) to the west of the house (N-S alignment) with nothing but bush and mountains for many hundreds of km (or miles) to the north and east.

Phase 1 will be the 90º – 270º (green) antenna. This will give me access to the east coast of North America (90º), something that eludes me at present. The opposite direction will hear the South Pacific and Australia.

At 400 meters (1300′) long, it is more than a full wavelength at 160m and about 0.6 wavelength at 630m. It should work quite well as long as my ground resistance is not too low … we’ll see how that goes.

Phase 2 will be the 120º – 300° (orange) antenna. This will face the American mid-west and South America (120º) with the 300º end facing Eastern Asia (Japan, Philippines, etc.).

Phase 3 (red) is the experimental antenna. It faces Europe at 30º and New Zealand at 210º. The reason it is experimental is that I live on the southern edge of the auroral oval. Europe is directly through that oval all of the time and I cannot hear stations on that side of the world with my present setup.

What will I hear on the beverage? I’m not sure but that’s why I want to build it …what will actually happen? The nice thing is, I can move the antenna bearing if I do not like the result.

I’ll leave this post with that thought and check in again with the 2-wire transformer boxes and feedpoint switch.

DGPS signals

I had noticed some louder, wide bandwidth signals , compared to CW NDB signals, in the “NDB band” and was grumbling about them covering up some possible NDB signals.

It turns out that they are DGPS (Differential GPS) stations that transmit (continuously) information about the GPS satellites, their errors and their health. Other messages are sent listing other surrounding DGPS stations, etc. Check out the DGPS guide (PDF) for more information.

I tried to decode the stations using Spectrum Lab software but cannot seem to get the terminal (decoder) program to hear the signal to decode. Everything else seems fine, the terminal is “connected” to the right point in the virtual circuit … I’m stumped.

I suspect that I have missed a step or two in the setup sequence. Note that while Spectrum Lab is quite powerful, part of that power comes from it’s complexity and ability to be configured in many ways. This means that there are many ways to set up the software … and many ways to “break” it so that it does not do what you want. I’m in the latter category right now and need to learn more!

I found that DSCdecoder (trial version) works flawlessly for DGPS signals. It also covers DSC and Navtex signals so I need to try those out as well.

There seems to be a different problem now … I do not have enough time in the evenings any more!

DSP and NDBs

The HDD arrived and I have a computer again!

I’m using Spectran to examine the audio output of my IC-7000.

I had good success using my ears alone in identifying weak signals but the waterfall display helps identify the really weak ones. I can also narrow the digital audio filter to 1 or 2 Hz to separate two or more signals on the same (or very similar) frequency.

I’ve picked up a few signals that I would not have known were there (using my ears alone) with this technique. The one thing that is nice is the duration of the waterfall (many seconds) helps me identify the non-DAID (no dash after ID) signals. I know I was moving through the correct frequency on their silent time between IDs. Now I can see the signal before or after I arrive on frequency and can set up correctly to receive them when they transmit.

I’ve noticed some wider bandwidth signals in the middle of the NDB band. They seem to be digital.

… Research …

They are on the correct frequencies for DGPS signals so I’m going to need another software program to decode them. I’m looking at WSJT for this but the learning curve is quite steep.

More later as I figure this out.

EDIT: It looks like Spectrum Lab also can decode DGPS … I have a better grasp of how that program works so I’ll start there.

EDIT 2: I can’t seem to get the terminal section of Spectrum Lab to “see” the signal. Obviously I have done something incorrectly. I loaded DSCcoder and it works great. I’ll keep testing it for a bit to see if it is the software for my situation.

Computers and signals

I’ve dabbled with computers, SDR systems and software for spectrum analysis on my HF radio for a few months (more off than on) and have not really thought too much about these tools. Then the computer decided that the HDD was no longer a HDD and stopped working completely last month.

When this happened I said “Oh well, I don’t use it for too much so it can sit on the shelf for a bit”. This turned out to be the opposite of what I really should have done!

I’m at a point in my NDB hunting career where I have heard most of the signals that are audible on a normal evening. On quiet nights with good propagation I’ll hear more but I feel it’s time for some new strategies.

One is building a loop to null the “loud ones” (it’s on the project list) and another is digital signal processing (DSP).

Weak signal detection using DSP can allow me to “see” the signals that I cannot hear well (or at all). I can also use programs that will decode digital signals or display QRSS (slow speed CW) easily. Recording is also possible with these programs so I don’t have to stay up late every night!

So now I’m at a standstill as my computer is not working. I ordered a new (old PATA style) HDD and it’s on the way. Once here, I’ll rebuild the computer using some backups I have (you have backups don’t you?) and re-install other programs. I should be back up to speed by month end (I hope).