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Another antenna option for the RTL dongle


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I got the following from usd.dx.com, and I am pleased with the performance boost they provide, although I am judging based upon an ad hoc evaluation of signal strength of FM radio streams.

Obviously, no antenna is perfect for every frequency, although the composite dipole antennas seem to provide good performance at wide bandwidth/wide variety of frequencies, but look like a throw back to the TV antennas everyone used in the 70's and basically, before Satellite and cable tv service was the defacto standard.

However, the gauge of the wire, and the overall construction of the antenna I bought seems to be a big step up from the antenna included with the dongle, for the frequencies I am looking at.

Here are links to the antenna I am playing with:

http://usd.dx.com/product/portable-digital-dvb-t-tv-25dbi-omni-magnetic-based-aerial-booster-antenna-iec-901030061#.UydkzfldVOI

To connect it to the Realtek dongle from the Hak5 store, you will also need:

http://usd.dx.com/product/lwj-023-mcx-male-to-tv-female-antenna-adapter-cable-black-17-5cm-901207418#.UydmkfldVOI

The antenna has a nice large base, and is beefier in size than the included antenna in the realtek dongle packs, and it seems to perform well for a general purpose Omni. Oh yes, the base is magnetic, so make sure you don't leave it on those vintage 5 1/4" floppies you have laying around. It, even with the adapter cable, is cheap, and this is usually a consideration for most of us. usd.dx.com also offers free shipping if you are willing to be somewhat patient. Everything you order from them arrives... eventually ( 1 1/2 to 2 weeks delivery is typical ).

I almost hate to say it, but there are also Realtek dongles that have the larger antenna connectors built into the dongle, so you don't need the adapter cable if you are using a variant ( from another source ) of the Realtek dongle from the Hak5 store. Maybe the Hak5 store will start offering the other dongles with a more general/larger antenna connector. Signal is everything with radio. So, every connector/adapter you throw into the mix is going to drop signal strength a bit, especially when you drop the gauge of the conductor ( wire ) down. I understand the argument for the Hak5 dongle, you don't need to worry as much about position or it getting in the way of another usb Cable, but I just use a short USB extension cable. Having a cable in betwixt the dongle and the computer is completely different from strangling the signal strength coming into the dongle. Once RF makes it into the dongle, everything is USB/digital out to the port on your computer. Having the radio slightly away from the main body of the computer also has some benefits ( with the Hak5 dongle included in this mix ) as the location of the dongle away from the computer allows the dongle to not be blocked by the body of your computer ( if you are using a desktop ) which can have negative effects, also possible is RF interference from the computer, so my general opinion is the dongle works better off of an USB extension cable, but I use a lot of desktops, because the performance of desktops and the peripherals are in a form factor that makes modifications/maintenance much easier, and Notebooks are designed with battery life as a major consideration, so with less power, comes the consequence of less performance. I use a mix of desktops and laptops/netbooks/android devices, but the smaller form factor devices are mainly used for browsing and SSH or RDP'ing into my other servers/workstations, or other applications where mobility is more useful.

My desktops are where I do most of my linux/FreeBSD/Solaris server or development/programming boxes, and my gaming.and Windows 7. One of my netbooks ( Intel Atom ) runs a nice linux distribution specifically designed for it, with a desktop that is oriented towards the smaller screen size. The others run Windows 7. Usually, if I am programming or doing things on the Linux/FreeBSD/Solaris boxes, I use RDP or ssh from a windows 7 box unless I need higher graphics/audio performance, then I do it on directly from the console of the host machine. I used the atom running linux for many years for most of my web browsing before I went to my dual core AMD netbook. The atom runs cooler and longer on the battery, the AMD cranks out the heat, but also has a nice bit of performance and can even limp along in most games. More heat from the computer means more performance. The netbooks are also convenient for working with microcontrollers, as far as programming them. I work with both Pic and Atmel microcontrollers, and a netbook is more appropriate for updating the code, especially when the microcontroller is already deployed in an application. ISP on Atmels pretty much means you need to drag the computer to where the microcontroller is doing its thing. The pics I use are socket oriented, and I can pop them out and drag them back to my Olimex Pic programmer. I don't debate which is better, as far as Pic vs Atmel. It is sort of like Apple vs Windows. I just don't care. I use whatever is best for the project.

I have seen some people try to claim that newer computers are more environmentally sensitive, but in my experience, the more heat a computer cranks out, the better the performance. I also used to support data centres, so I have a bit of experience in power consumption, performance, and cooling issues. If you aren't familiar with HVAC/cooling issues with computer servers, you aren't working in a data centre that even qualifies as small scale, or you are running servers in Alaska.

I have rambled, and I apologise for some of this, but I have learned so much about computers, electronics, programming, and networking that my mental wiring is partially fried, so consider anything I write as a partial core dump from my main CPU. When I went to school, I was usually kicked out from the computer classes and told to go work in the library on my projects, and just turn in the work at the end of the day, or the end of the quarter. Teachers found my breadth of knowledge to be intimidating, and my social skills to be largely undeveloped. I couldn't help it if I knew more than my teachers, with the exception of my coworker at Heritage College who was the head of the Computer Science department. He is a smart cookie, and was quite enjoyable to collaborate with, as well as learn from. Come to think of it, he was the only computer prof I had that didn't kick me out of his classes.

-FuzzyBunny

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These are the specs of the antenna, but I am still testing and comparing it to the base antenna included in the Hak5 kit. I will post my results when I composit more data and observations. The length of the antenna cable also seems to help a bit. ( Ham technical description: long piece of wire ) Although it suggests using it with car/mobile applications, but I have found it functional for base station operations as well.

Enhance the signal strength, reception and picture quality
- Integrated 25dB low noise amplifier
- Magnetic based mounting make DVB-T Antenna be placed much easier
- High gain amplifier, ideal for DVB-T Digital Terrestrial TV Receiver
- Super easy to install, no drilling required, put it on the car roof or above the -
trunk with its magnetic base, fits almost every cars
- Portable DVB-T Antenna is removable, therefore, also convenient to set while washing
your car and in the three-D parking area
- Frequency: VHF (174~230 MHz) & UHF (470-862MHz)
- Signal Amplification: approx.25dB
- Radiation: Omni
- SWR: 1.5:1 (Max.)
- Cable length: 195cm

-FuzzyBunny

Edited by fuzzy_bunny
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Odd. All recommendations I've encountered so far were for a short as possible cable between the card and the antenna.

Well, the "cable"/feed line betwixt the antenna and the card is just a wire, so if you are overly concerned about the frequency precision of the antenna, I could see this as being valid, if the wire were unshielded or unbalanced, or the distances were really long ( like electrical transmission/distribution lines, where line resistance, "skinning effect", and other considerations need to be taken into account to preserve power from unnecessary line loss, but here we are talking about hundreds of miles ( Transmission ) or < 100 miles ( distribution ) of electrical power ).

In short wave listening ( almost a dead art form ) using a long unshielded/unbalanced piece of wire is frequently used, even though it isn't tuned to a particular frequency.

Also, the longer the wire, the higher you can get your antenna, and in picking up radio broadcasts, the higher the elevation betwixt the top of the antenna and the level of ground is generally almost 100% of the time, a bonus. Radio waves get absorbed by the ground, buildings, ( metal siding ), so the longer the wire/feed line, the more likely you can get both higher and/or closer to the window. Shielded/balanced feed lines are also somewhat different from single conductor antenna wires, so we must be mindful of the difference betwixt these two designs/mediums.

Professional radio stations don't use tall towers because they look pretty, they use them because they broadcast the signal over more obstacles ( and because of the power being used ). Short wave broadcasting arrays ( such as Voice of America/US AFRTS faciliities in Westchester, OH ) use many very long, heavy gauge antenna arrays oriented in different directions for their various broadcast destinations ( tuned for the wavelengths they are broadcasting on ). Ham radio operators, who have a choice in the matter, don't use a short feed line to receive from, and a long feed line to broadcast from, they try to get their antenna as high as possible. Generally, the higher the altitude the better, or if indoors, the closer to a window, the better. Obviously, receiving a signal we are dealing with just a small portion of the power we are dealing with when we broadcast, and the signal is already "in the air" from the tall transmission tower, so reception antennas tend to be shorter on portable receivers ( automotive based, or handheld ) as a matter of practicality, not really efficiency. Base stations ( transceivers ) still use long feed lines to their antenna towers, because they perform better at higher altitudes. A difference also exists betwixt receiving a signal at 88 MC/s vs 2.4 GC/s, so it really depends on your environment and the pluses you are trying to get at ( altitude, or proximity to a window ) vs the minus of the length of your antenna feed line ( interference on a long feed line usually comes from EMI/RFI rather than the resistance of the wire or the practicality of having a long antenna ). For your WiFi, you really don't want your signal going too far outside your house ( generally ) as you are trying to not conflict with others' use of the same spectrum space, and avoid them conflicting with yours, ( Part 15 FCC rules ) so the objectives are somewhat different, and the wavelength determines the optimum size of the omni's. When you are attempting to receive distant signals, the objectives and ways to achieve those objectives are completely different.

The resistance in your typical copper wire is pretty negligible for the length of spans we are talking about, so having a short feed line isn't going to assist with signal strength as much as having the antenna placed somewhere free of obstacles and as high as possible. Also important is the characteristic properties of the signals we are dealing with, and whether we are depending on bouncing our signal off of the ionosphere ( or some people have bounced their radio transmissions off the moon... ), or whether we are dealing with more of a "short haul" transmission/reception objective, such as FM Broadcast Radio.

-FuzzyBunny

Edited by fuzzy_bunny
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"Short wave broadcasting arrays ( such as Voice of America/US AFRTS faciliities in Westchester, OH ) use many very long, heavy gauge antenna arrays oriented in different directions for their various broadcast destinations ( tuned for the wavelengths they are broadcasting on ). Ham radio operators, who have a choice in the matter, don't use a short feed line to receive from, and a long feed line to broadcast from, they try to get their antenna as high as possible."

Sad to say, VOA in Westchester (Bethany Relay Station) has been silent since 94 and the antennas are gone. {sniffle} Also - I regularly go out with a bag of dope and get my antennas as stoned as possible to help improve the signal quality. :lol: - KD6W

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