Posts Tagged ‘doppler’
The modern way of getting (simply) into 10GHz WBFM appears to be using very low cost 10GHz Doppler radar modules with a 100MHz FM receiver. Whilst with G6ALB for my Pixie tests Andrew demonstrated a working 10GHz link based on these low cost modules. These are useful links Andrew sent me.
Hi Roger,These are the units I found when I was looking for [definitions of] the 10.525 GHz ISM band.It looks like 3cm Doppler radar is alive and well,I’d assumed it had disappeared in favour of PIR.Some data here:These are very good pages (for wideband FM on 10 GHz).
CX2ABP(11127km) in Montevideo (GF15wc) has just been spotted here at -25dB S/N on 10m WSPR even though propagation is supposed to be “poor” and he is using 5w.
10m really is my favorite band of all. Propagation supposed to be “poor” yet here is a South Anerican 11127km away on QRP! Now he is -21dB S/N and getting better!
UPDATE 2015z: Weak highly Doppler shifted signals near the bottom of the WSPR band suggest there is some 10m GDX about too. With luck, this may decode before too long? It needs a period with low Doppler.
UPDATE 2050z: CX2ABP has now been spotted 4 times in the last 38 minutes and he is now -18dB S/N which is 7dB stronger than at first. Again, it may be just co-incidence but his best signal corresponds with when Doppler on his signal is lowest. It is as if ALL stations with any drift or Doppler are best when Doppler (or is it drift?) is lowest.
UPDATE 2111z:: Nothing seen since 2038z, so I suspect the band has died out for the day (or the software has ceased working again!). Maybe I should go back on 6m looking for GDX again? I’ll leave it on 10m for another 20 minutes just in case.
UPDATE 2132z: Gone back to 6m GDX hunting. All quiet here so far this evening.
Today, so far, it has been exclusively local G4IKZ (18km) on 6m WSPR One thing I have noticed both on his spots and those by G4FFC (45km) yesterday is that when there is a lot of Doppler my reports are poorer. I assume the aircraft reflections sometimes result in destructive interference and an effective drop in S/N.
This month, so far, sunspot numbers have been lower (70 today), although 20-30MHz propagation is described as “normal”. I think the slide downwards is starting, sadly. But, even next autumn 10m should still be good though – we are a LONG way from the minimum yet. I think long distance 6m F-layer propagation openings will be few unless one is lucky enough to be closer to the equator and may catch TEP openings. CN8LI and stations in Israel were managing to catch 6m TEP openings quite recently, as were some VK and JA stations.
UPDATE 1700z: Just G4IKZ (18km) spotting me since I switched on 6m WSPR at 0556z – a very very quiet day on 6m so far today: no Es and no GDX seen here, so far. There is at least one “wandering” signal that has been seen several times drifting across the band but with too much drift to decode. Strong, but no Doppler. At one point it was stable enough to decode but the signal faded out after 1 minute. I think this was an Es signal. May never know though. I am tempted to QSY to 472kHz WSPR this evening unless things markedly improve on 6m.
UPDATE 1808z: another new local(ish) station has just appeared on 6m spotting me: M0MVB (30km) up in the Fens. Still no 6m Es here.I presume M0MVB is just in from work and just turned the gear on.
UPDATE 1925z: Still no 6m Es here today. Tomorrow can only be better.
UPDATE 2050z: I stuck with 6m, but only locals today. Very disappointing indeed.
As I’ve mentioned before, KD2CHE and I belong to a local transmitter hunting group. We get together one or two times a month. One member will hide the box and give us a general area, which is usually a radius from a point (i.e. 2 miles from the intersection of routes 1 and 2 in Anytown, NY). We are the only ones without doppler equipment, yet we almost always find the transmitter. Here’s some pointers for those of you that enjoy a bunny hunt every now and then, but may not think you can participate without sophisticated direction-finding equipment, or for those of you with dopplers that want to refine your techniques.
First of all, when I know the area, I print a map from the computer, and draw a circle for the hunting area. Then, using either our knowledge of the area, or a combination of Google Maps, and Bing Maps, I find a large building that I can drive all the way around, as close to the center as possible. I mark the spot on the map as our starting point. KD2CHE drives, while I navigate. When the time comes to leave for the location, I load up the equipment:
- The mobile in the car, for communicating with the other hunters, an Icom IC-207H
- An older Kenwood all-mode 2 meter mobile, with an RF-gain control, attached to an OPEK micro mag mount antenna
- A smartphone with Google Maps, or a laptop with a broadband connection
- Bright flash-lite
- 1 HT set to the third harmonic of the hunt frequency, usually my Icom IC-T90A with a good antenna
- 1 HT set to the hunt frequency with the antenna off, usually my Baofeng UV3R MkII
- 1 HT set to the hunt frequency for KD2CHE to use out of the car
Once the transmitter is activated, KD2CHE drives slowly around the building at the starting point, stopping when the transmitter stops, and starting up again when it comes back (the one we use is usually 30 seconds on / 30 seconds off). I mark the points in our loop where the signal was strongest and weakest, drawing a line with an arrow to get our initial vector. Then we navigate in that direction, using Google Maps as a guide. As the signal changes I mark the observed strength on the map. When we reach the point where the signal strength goes back down, we determine the high point, and KD2CHE drives as close to perpendicular to the original route as she can.
During this process, the RF gain control on the Kenwood comes in handy. The box puts out a full 5 Watts, so as you get close to it, an un-attenuated receiver becomes useless. For the signal readings with the RF gain all the way down, I write an ‘A’ in front of the s-meter reading on the map. As the strength goes up again, we keep an eye on the 2 HTs. When we’re within 1 or 2 blocks, one or both of them will become active. The third harmonic will usually not work until you are almost on top of the transmitter, which comes in handy. This is when we start looking for a good spot. In many cases there will be a public park, or area of some sort nearby, and the rest of the hunt is done on foot with the HTs, and the flash-lite if necessary.
Body shielding will get you a direction to walk in. Hold a radio that is getting a weak signal (the IC-T90A has a fixed-level attenuator I can activate) close in to your chest and slowly turn around, and make note again of the weak and strong points in the circle. Keep in mind though that sometimes, a good hider will put the box in a location that creates reflections and ghosts. Sometimes you just need to use logic, or in the case of our last hunt, KD2CHE found the box simply by looking, while everyone else was wandering around the woods with Yagis and other fancy equipment.
Of course it helps to know the area, and to have some insight into where people like to hide things. One of our hiders frequently hides in places he discovers while hiking. Another likes to hide in very unique, and sometimes questionable places. Once or twice we’ve had to explain to the authorities what we were doing.
I’m convinced that a doppler might enhance our abilities, but I’m afraid of relying on it too much. We actually have one, but it needs some work. We’ll see.
73! Neil W2NDG
Richard is back and everything is right with the world--except Russ. Plans are in the works for setting up at the Dayton Hamvention. Many thanks to all of our listeners who donated to the cause. Our next donation goal, is $150 to get a noise gate for Richard. We know at least a couple listeners who should be happy about this, and we suspect there may be a few others out there. Of course, we're committed to improving the quality of the program whenever and wherever possible.
This episode is a little heavy on the radio side of things. However, don't be deterred. Richard gives us a lot of great information about satellite technology, concepts such as Doppler shift, transponders, antenna polarization, the science of orbits and much more which will appeal to your inner geek whether you're into ham radio, computers or just science and technology in general. Have a great week, and we look forward to seeing everyone in the chat for the next live recording on Tuesday, March 2nd.