SDR / Antenna / Super Basic Questions - Page 1
Forum section: electronics / rf-microwave

author: Electro Fan
author_rank: Super Contributor
timestamp: February 01, 2016, 01:15:04 am
content: I've been using a SDRPlay with HDSDR software. I've pretty much figured out the SDRPlay software and the HDSDR software so I've moved on to antenna 101 stuff. After enough FM listening with an indoor dipole antenna I decided to look for some CW signals at the likely frequencies below 28 MHz and around 147 MHz, but I didn't find any. I used the FM dipole for 147 and a plain wire antenna for everything else.Frequencies 1.8025, 3.5815, 7.0475, 14.0475, 18.0975, 21.0675, 28.0675 and 147.555 MHz.So next I tried the 2.5, 5, 15, and 20 MHz time broadcasts on AM. I experimented with various lengths of wire and was finally able to barely receive the 10 MHz time signal. In working on fine tuning the software to get a slightly better than barely hearable signal at 10 MHz the signal just disappeared. It could be that something toggled in the software but I'm also wondering if it could have been the transition from the sun being up to the sun having gone down - it seemed to occur around sunset.Any thoughts on why it might be so difficult to hear the time stations or ideas on how to better utilize a plain old wire antenna (I calculated that a 10 MHz signal should have a full wavelength of 30M and tried full, half, and quarter lengths of wire; quarter seemed to work the best but still not great).Thanks for any advice.Update: found some related info on WWV time of day considerations but still trying to figure out why it's so difficult to get the WWV stations at night.... will try again tomorrow during the day to see if they tune in better then

author: cdev
author_rank: Super Contributor
timestamp: February 01, 2016, 05:03:46 am
content: The skip zone varies by frequency and time quite substantially. Also, your ground is important, that is half of your antenna.Use a length of coax to connect your antenna to your receiver, with the center going to the antenna, and the shield going to a groun or counterpoise.Right now I am listening to lots of CW activity on 40 meters, just a bit above 7 MHz..Another good receiver testing tool, is the digital modes program WSJT-X. Once your receiver is operational.You can always hear digital modes at 7.076-7.079 or so at night and 14.076-79 daytime. Different digital modes have different characteristic sounds.Something sounds badly mis-connected. A bad cable, most likely. Check that first. For continuity.HF is more like DC than like UHF/VHF. You can even use speaker wire instead of coax, in a pinch, if you make sure to observe polarity re ground side. It works surprisingly well. (Characteristic impedance is typically around 90-100 ohms.)Do you have any big variable capacitors lying around, we'll get you receiving stuff.Is it night where you live now? Honestly, you should always be able to receive quite a bit at all hours of day or night.to see what's happening in terms of propagation, go tohttps://www.pskreporter.info/pskmap.html- look at their map.Then zoom in on wherever you are and look at what QSOs are happening with your neighbors, you should, with a little bit of work, be able to receive some of the same signals on the same frequencies. Read up a bit on radio propagation.It varies a lot. There is something called the "MUF" - the "maximum usable frequency" - which goes up in the daytime and down at night. Signals travel farthest closer to, but not above the MUF.Bands below 10 MHz generally will be better at night, and those above 10 MHz in the daytime. Right around sunset and dawn, are the best chances to hear signals that have traveled for very long distances.Also, bookmarkhttp://www.short-wave.info/index.phphere is another good resource, in a more readable format..http://www.dxing.com/tuning.htmIs there a lot of noise where you live? If so, then you may need a different approach. One that decouples your receiver from the (often common mode) noise.Do you have any RF-appropriate toroids lying around? Or even an old 4:1 TV balun, that might be helpful for its binocular core- to isolate your antenna from power noise, etc.You can buy a toroid which you can use in one for a few pennies here:http://www.kitsandparts.com/toroids.phpYou will also need a few inches of wire. No need to spend any more.if you have a toroid, you can make a "9:1 unun" to better match the impedance of your wire antenna to the receiver. Put the roroid near your antenna.if you have a binocular core, we might as well make a balun.If you have a fairly decent variable capacitor, and some wire, and a bit of coax you can use to run the signal to your radio, you can make a quickmagnetic loop.If your radio cannot receive lots of stuff with a decent antenna, you got a bum unit, and if so, you should get an RMA then, and send it back.HF is crowded, especially at night - and barring some solar disturbance, almost everywhere you look there is stuff.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 02, 2016, 02:58:32 am
content: Quote from: cdev on February 01, 2016, 05:03:46 amcdev - Thanks! I've had some very helpful replies to questions on EEVblog over the last couple years but yours is right up there. I appreciate the very comprehensive and insightful suggestions. I'm going to work my way through each of your suggestions and see what I find. I have a hunch the solution is likely to be somewhere on your list including the possibility that there is an issue with the SDRPlay - but it's probably some type of user error.Whatever it turns out to be thanks for the time in putting together all the info - it is really very informative given where I am so far with the SDRPlay and HDSDR.I'll let you know what I figure out and please feel free to add any other suggestions or other thoughts. Thanks again, EF

author: cdev
author_rank: Super Contributor
timestamp: February 02, 2016, 07:13:56 am
content: I know exactly how it feels, I am struggling with something exactly like that right now, its definitely writeup-worthy when I finally get it worked out.Feel free to PM me if there is something I can help you with.I would try making a 9:1 unun if you have a toroid in even approximately the right kinds of materials. Like the rtlsdrs, most SDRs to varying degrees degrade very rapidly in the presence of certain kinds of noise, and often its silent, they just stop receiving signals you want to hear.I would try a unun, the effect of which I think is best described as sort of smoothing everything out.. A unun can make reception dramatically quieter sometimes.Don't neglect the ground part of the antenna. The better you get the ground side dealt with the less noise you are likely to have.Do you have an rtlsdr you can compare the new one with as you tune across the bands?I find my rtlsdr is really useful in terms of reliably giving me a sort of wide view of whats going on on certain frequencies to get your other equipment performing as its supposed to.Thats especially useful when you're working with something that has a DDS in it, which can sometimes leave you receiving signals you have no idea what their frequency actually is, sometimes reversed. Sometimes - garbled..I find a lot of very strange sounds. That's one of the main draws of radio for me. I capture a lot of samples and who knows, might be fun to use them in music or some kind of art at some point.Like, for example, right now I am having some issues with my band pass filters being quite confused.My RTLSDR is proven to be invaluable in figuring out what is happening. I just leave another instance of Linrad running with my RTLSDR basically all the time while I am troubleshooting. You just need a separate directory for each one, to launch it it.But don't connect two SDRs to the same antenna, at least not two sensitive ones. Not even with a splitter. They will both interfere with one another.You need a little LNA to isolate each one.

author: MSO
author_rank: Contributor
timestamp: March 24, 2016, 04:31:10 am
content: cdev,I'm not the OP, but thought I'd echo his comments. I've found your posts to be very informative and helpful. Thanks for taking the time, it's much appreciated.