300 - 450 MHz for SDR

[299792458]

Can anyone recommend a good antenna for use across 300 - 450 MHz range? I'm doing a couple of new SDR projects to monitor things the 300 - 450 MHz range using an rtl2832u (820T).

Is a simple telescopic-type antenna the simplest best solution? Any recommendations? Standard requirements: I desire receive only, omni-directional, and high gain. Currently doing development only (so something simple and portable would be nice for the near-term), but eventually would like to have a permanent setup for it in a good location alongside my ADS-B stuff. And then I'd like a discone multi-purpose too, but that's another story.

 

[k9rzz]

How do you get high gain (what's high gain? 5db, 10db? more?), omni-directional, over a 150Mhz span? Certainly a discone would be best, but I would say put up a ground plane cut for the lowest frequency, get it up in the clear, and use low loss feedline. That will give you close to unity gain, omni-directional coverage over your desired range. How well it hears depends on how well you you get it in the air and how good the coax is. Good luck!

 

[Russell]

Nothing beats 30 - 40 ft up; the higher the better. LMR 400. Some use a pre-amp but in my area (metro DFW) a pre-amp could over load your receiver. I've seen a signal splitter used at the antenna with one line using a pre-amp and the other 'not'. Pretty cool set up allows you switch back and forth. If you got the bucks, etc. then use a rotor and a yagi.

 

[299792458]

Thanks, those are useful comments. For k8rzz, essentially high gain is relative, right...at least literally speaking...so 3 - 5 would be great, but right now I'm stuck with some pretty poor options and am looking to improve. Perhaps 2 separate antennas may be better.

On a side note, I do have a little experience in this area, but have enough humble sense to listen to experience. I haven't done anything this low before so I appreciate the feedback about the discone. I'm essentially looking at frequencies in the ~320 MHz and ~430 MHz ranges (roughly 70 cm and 94 cm). I'm not using an appropriate antenna right now (combination of junky cheapo antennas), and I'm looking to improve but also excel. Perhaps I should just get a discone, mount it, and see if I'm still wanting more. That would serve another purpose in scratching my itch to get one for other reasons!

Point taken on high quality cable, this is one area I'm picky about. The last one I built cost me $1.49/foot (for semi-flex LMR-400, plus connectors) but I think even those prices have dropped. This is well worth the investment, even over pre-built cheap cables.

So if I want a all-purpose monitoring antenna anyways, you think I should get a discone first then see if I need more?

 

[k9rzz]

I think you could run RG-6 at that frequency and never notice the difference between it and LMR400 (3db/100ft). Are you really going to be digging in the noise that much, like you might be if running CW/SSB DX on 432? I think the satellite biz uses something like 900 mhz for the I.F. between the feed and the receiver, and they all run RG-6 for home use. The money you save on that coax run would probably pay for your discone right there. ~:^]

I use 100 ft of RG-6 for my serious FM broadcast antenna stack and I have to use an attenuator before the receiver. No problems with loss at 100 mhz that's for sure.

 

[299792458]

So at 300 MHz ya, difference for 300-400 MHz is a db, db and a half. I'm kinda looking to listen and reach as far as I can. I ended up springing for a Comet discone, will be here tonight (yay!).

I anticipate making use of broader range on this antenna so I will still consider LMR400.

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