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SDR fun


m1k
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Hi all,

as an old ham radio operator I am very interested on SDR and all related to it.

I got my ham license some 30 years ago and I was playing with TNC's,antennas,rf power tubes for a long time.

That said,back to SDR.

These dongles are fantastic...You can do almost everything (receiving) and they are very cheap.

From my personal experience....the one with the Elonics tuner (E4000) is the best.

Sensitivity..frequency range...construction...rocks!

Just one downside...it comes usually with the standard tv connector.

PLEASE....do not use any adapter!!!

Just desolder that ugly connector and solder on the board a 5 cm. of rg58 and a N Connector.

Keep cables very short...and use quality connectors....(soldering an N male connector is an art!)

I got a lot of links on mods....converters and antennas...if You are interested....just drop me a line and I will

share.

73's

IK6....

;)

Edited by m1k
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Interested for sure. Planning on getting my first SDR in a week or so which will have an R820T (see other topics here).

What I'm also interested in is your remark "soldering an N male connector is an art!" - what caveats are there? It seems simple enough: use some solder to connect wires to specific metal parts of the connector and see to it you don't get big lumps of it next to your joint and that you don't connect stuff that's supposed to remain isolated. Oh, and don't burn any nearby plastic with your soldering iron. Am I missing something?

I haven't done much soldering thus far, but I'm planning on constructing my own antennas for Wifi which will obviously involve some of that. If there are lessons to be learned up front, I'm very much up for that.

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Don't use acid core solder. For ease of use, lead based solder is easier to work with, but has been banned in the EU. Using the environmentally friendly ( 99-1? ) solder requires higher temperatures, and is in general, harder to work with without damaging the board or components than using lead based solder, which works at a lower temperatures.

As for lead being an environmental hazard as it is used on PCB's... eh, whatever. If the EU says so, it must be true.

-FuzzyBunny

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Meh. Over here at least the rule is that so long as it's not in (commercial) volumes, you're free to use lead-based solder. It's readily available.

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Perhaps he meant soldering SMT is an art, which even if it doesn't qualify to go into an art exhibit, at least it does require some degree of skill and steadiness in the hands.

High skill in anything is an art form, and some of the Chinese boards I have seen have shown the opposite side of the spectrum ( really, really, _bad_ connections and style ), as well as some that have been as well produced as anything I find made in the West.

Sometimes the most apparently simple things are also paradoxically the most difficult to do well, although as far as soldering goes, I have been doing it long enough that I pretty much take my own ( admittedly craftsmanship laden ) work as a matter of course, as I also take my own humility for granted.

-FuzzyBunny

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Im not sure about the e4000 sets but iirc these usb sdr sticks are using 75ohm. I think this traces back to the fact that they were used for tv which uses 75ohm coax. RG59 may be a better choice and is available at home depot etc. where RG58 (50 ohms) is a little harder to find at local shops. Specs can be found here http://www.rtl-sdr.com/about-rtl-sdr/

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My mistake.

Of course,being a device intented for dtt reception,cable impedance is 75 Ohms.

So You must use Rg-59.

You can buy in every Ham-Shop (if they still exists!)

;)

Edited by m1k
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My mistake.

Of course,being a device intented for dtt reception,cable impedance is 75 Ohms.

So You must use Rg-59.

You can buy in every Ham-Shop (if they still exists!)

;)

Standard MCX connectors are 50 ohm.... SMA connectors are 50 ohm.... You can get 75 ohm MCX connectors but they are 10-15% more expensive as they are not "common" for RF use....

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Standard MCX connectors are 50 ohm.... SMA connectors are 50 ohm.... You can get 75 ohm MCX connectors but they are 10-15% more expensive as they are not "common" for RF use....

also..... most of the small jumpers from MCX to SMA...even the "F" are made with RG316 cable... which is also 50 ohm.... Why does everyone use 75 ohm cable to make antennas for 50 ohm radios (DVB-T Dongles) ?

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One USB SDR mod I did was internal shielding to lessen the outside RF from getting into the radio. Second thing I did was remove the USB connector and put in a pig tail without a shield braid in it. This also keep computer side RF out of the radio. A design flaw in most all SDR's is the USB shield ground and the USB -5 VDC lead are tied together electrically and this in turn turns the whole USB cable shield along with shield grounds in your PC into an antenna thar feeds direct into the radio thus causing a high noise floor and random spurs from PC clock interference.

Easy shielding can be done by wrapping the sdr in plain tin foil and using an extension USB cable that has no shield braid.

As for the antenna connectors I left mine intact and just purchased some adapter pigtails to take it to an "N" type connector.

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