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Shortwave reception (SDR)

Posted: Tue Mar 14, 2017 6:57 am
by blueshift16
Hi, I'm trying to use my SDR dongle with DSDplus to decode p25 in my county, (our police radio). After some hard work everything is finally working but DSD is struggling to decode efficiently and its because I'm not receiving a good signal using the antenna that came with my usb dongle. I know antennas are a science and I appreciate that (now) but without splitting the atom over here would someone be so kind as to share with me how I can better receive 460.500 mhz? (my local short band police radio) That should be fairly easy to receive I would think, no? I'm actually not that far from the transmitting tower either.

Do I need an expensive antenna for this type of reception? and let's say that I can't afford one, is there a cheap alternative like a tv antenna connected properly to the usb dongle? I mean that should be better than the stock antenna I would think but I could easily be wrong. Or is there a special antenna that can be bought/made for that particular frequency range. Man I really don't know.

I bow to the radio gods that are you guys; teach this young grasshopper so he doesn't have to spend 2 weeks on youtube trying to find an answer that might be wrong. Thank You.

Re: Shortwave reception (SDR)

Posted: Tue Mar 14, 2017 8:12 am
by rtlsdrblog
Which antenna did you get? Is it a telescopic one, or one of the cheap fixed length black whips?

Ways to improve your signal:

1) Get the antenna up high and outside with an unobstructed view of the horizon. Use USB extension cables, or reasonably short runs of high quality coax cable to achieve this.
2) Tune the antenna for the frequency of interest. For your whip you could search for a 1/4 wave groundplane calculator online, and use that to calculate the optimal whip length length for your frequency of interest.
3) For your magnetic whip, place the base on a large metal surface, or at least something like a cookie tin. This acts as a ground plane.

You don't need an expensive antenna for P25. The whip will be fine if you get it in a good location.

Ps. I'm not sure why you titled this shortwave reception? Shortwave refers to signals on the HF band below about 30 MHz. Your 460 MHz P25 signal is in the UHF band.

Re: Shortwave reception (SDR)

Posted: Tue Mar 14, 2017 11:51 pm
by walrusgumboot
A 460.500 MHz dipole will have each side 6" long so there's no need to go buying anything. Silver solder brazing rod would be good for the elements at that scale, or just thick stiff copper wire if that is to hand.

Re: Shortwave reception (SDR)

Posted: Wed Jul 12, 2017 11:11 pm
by syfr
If you're still here on the forum, I can help you with a yagi - type directional antenna that will provide significant gain, if you're even relatively handy with PVC pipe, small bits of wire and soldering skills.

We're talking a couple dollars tops here in materials.