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).

CLE 206 and an antenna upgrade

CLE 206 was an interesting time. I used the active antenna exclusively this time and was quite pleased with the reception.

I was not as pleased with the propagation on Friday night. For most of the night I was hearing my “big guns” (UAB, ZKI, PR and YD) but not much more. I was not convinced that this was an antenna problem because I could hear WT (Wrigley NT) as well. Later in the evening (morning?) I started to hear the weaker ones. I went to bed having logged all my previous signals between 190 KHz and 239.9 KHz and a new one for me, 206-EF (Castlegar, BC CAN).

Saturday night I stayed up later and picked up some new ones. I managed to hear most of the Alaska signals as they came up. The fun part of the night was spending time digging out two or more signals on the same frequency. I learned a lot about IC-7000 IF and audio filters … using tight bandwidths and the filter roll-off slope to remove one signal and hear the other.

It was raining on Sunday and so it was perfect for antenna work! I placed the active antenna in it’s permanent enclosure and raised it another 3 meters or so (10 feet).

 

Signals appear stronger but that could be wishful thinking.

EDIT: Great signals a few days after CLE 206 … hearing longer and fainter signals. A grand total of 32 new ones on April 27, 2016!

Kits in, projects out …

I received the LED SWR indicator (QRP only!) and the Digital Dial from QRP Kits today. Of course I had to assemble them!

The Digital Dial is a 4 digit frequency counter with some interesting features. It has a maximum frequency display of 45 MHz (just fine for LF/MF) and runs on a 9 volt battery.

image

I’ll be creating a custom crystal checker / frequency counter / digital dial  combination with this kit. One portable box for my QRP transmitter projects. I can also take it to hamfests for checking any crystals I wish to purchase as it will fit in my coat pocket.

Of course I need more bits to finish this off but that’s part of the fun.

The LED SWR indicator is used to tune up QRP antenna systems.  A quick visual indication of 50 ohm match when the LED goes out (or dim). It’s very small and extremely light weight for backpacking adventures (SOTA anyone?). This one is destined for the 1Watter, 160meter xcvr enclosure. I left out the LED for now as I’ll be measuring to fit once the PCB enclosure is complete.

LED SWR indicator

This, of course, will force me to start construction of the PCB enclosure. I don’t have a shear so other measures will be needed to cut the PCB. I’ll let you know how that works out!

Active antenna testing

I finished my active antenna this afternoon and stuck it on top of a 3 meter pole to see if it would work (to start with) and be an improvement (a bonus).

 

Since it was still daylight, the only NDB I could hear was the strong local (YD Smithers, 78 km). It was the same signal strength on both my HF-2V and the active antenna at S7. It passed the first test … it works. No more testing this afternoon as I have to go to town.

…

04:00z

After returning from town just as dusk was falling I wanted to see if the more distant stations I had heard on my vertical on previous nights would be audible on the new active antenna. After much fumbling around with questionable adapters I could hear the louder NDB stations (300 km or so) but no distant ones were audible yet. Time to wait for full dark.

…

05:00z

An NDB station I had heard only once some weeks ago … briefly audible above the noise … was 8C, Fairview Alberta (585 km). I had no problem picking it up tonight as it was quite a bit above the noise floor. For comparison, I switched back to the HF-2V where I had heard it before and it was gone … the noise had completely swallowed the signal. Nothing I could do with IF or audio filters could dig it out. Back to the active antenna and 509 (no measurable signal but excellent readability and clarity of tone).

Unfortunately (fortunately?) my noise level with either antenna is quite a bit below S zero so I cannot give any comparative numbers. What I can say is that signals that were in the noise and barely readable before are clearly audible now. The noise level is significantly lower on the active antenna. I don’t need as narrow a filter to achieve the same results as before. Narrowing the filter will probably give me more distant stations.

The active antenna is currently in a pill bottle on the 5 meter test mast (60 degree tilt) leaning on my carport roof. This is not the final packaging, permanent location nor the final height.

I’ll be reporting on how this affects my NDB station count in the coming weeks even though the darkness is waning now. The active antenna will be my main LF/MF receive antenna until the new station numbers start to fall off again. By then I may be ready for a vertical loop … null out the loud ones … who knows?