My Attempt at a $115 ADS-B Receiver Build for Foreflight

I added the 1050 MHz receiver and upgraded to version 0.4r1

I noticed it took longer to get a wifi connection. It also tended to drop out of ForeFlight. It seemed to get better using the power plug that came with the Raspberry pi, but it still dropped sometimes. I unplugged one receiver (978 Mhz only configuration) and it seems to be running better- doesn't get dropped in ForeFlight.

Am justified in suspecting I'm not getting enough power through the R pi to run both receivers? Would a powered USB hub help? I don't have the GPS and other stuff as I'm getting GPS via a Bad Elf.

It also seems to take a long time sometimes to get a wifi connection. Sometimes a few seconds, sometimes about a minute. This doesn't seem to matter how many receivers I have on it.

They are talking about this on reddit sounds like it could be an issue with 0.4r1 and is being investigated.
 
Anybody know if it's possible to have enough power to light up everything but not have enough power to support the receiver?

My Stratux has been rock solid for weeks. Tonight, while on ship's power, my wi-fi connection kept dropping off and I didn't pick up a single tower the entire flight (through areas in which I usually see 5-7 towers). In the air I tried rebooting both the Pi and iPad and also changed antennas, but never got it to work.

On the drive home, I recalled that I had switched out the usb lighter socket plug just prior to today's flight. I was getting noise from the one I had been using so I switched to a freebie that I picked up in Oshkosh. Now wondering if that plug may have been providing just enough power to light up the system but not enough to power the single receiver.

Can't air test again for a while but I am curious... think this is a possibility?
Jim
 
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Have you operated your rig with these antennas ? Do you have the antennas' predicted performance at 978 & 1090 MHz ? Hope it works as good as it looks.

I have flown at least 7 or so hours using them with no issues. At one point I switched with a set from a Skyradar unit and didnt see any performance diff.

If you havea SkyGuardTWX unit, it uses these antennas also.
 
Anybody know if it's possible to have enough power to light up everything but not have enough power to support the receiver?

My Stratux has been rock solid for weeks. Tonight, while on ship's power, my wi-fi connection kept dropping off and I didn't pick up a single tower the entire flight (through areas in which I usually see 5-7 towers). In the air I tried rebooting both the Pi and iPad and also changed antennas, but never got it to work.

On the drive home, I recalled that I had switched out the usb lighter socket plug just prior to today's flight. I was getting noise from the one I had been using so I switched to a freebie that I picked up in Oshkosh. Now wondering if that plug may have been providing just enough power to light up the system but not enough to power the single receiver.

Can't air test again for a while but I am curious... think this is a possibility?
Jim

What software version? I can run 1 but not 2 receivers, wifi takes longer to connect with the current version, see my post earlier and the reply.
 
What software version? I can run 1 but not 2 receivers, wifi takes longer to connect with the current version, see my post earlier and the reply.

Version 4r1 does hace issues but i just saw 4r2 posted, maybe thats fixes the issues
 
Anybody know if it's possible to have enough power to light up everything but not have enough power to support the receiver?

My Stratux has been rock solid for weeks. Tonight, while on ship's power, my wi-fi connection kept dropping off and I didn't pick up a single tower the entire flight (through areas in which I usually see 5-7 towers). In the air I tried rebooting both the Pi and iPad and also changed antennas, but never got it to work.

On the drive home, I recalled that I had switched out the usb lighter socket plug just prior to today's flight. I was getting noise from the one I had been using so I switched to a freebie that I picked up in Oshkosh. Now wondering if that plug may have been providing just enough power to light up the system but not enough to power the single receiver.

Can't air test again for a while but I am curious... think this is a possibility?
Jim

I can tell you from my experience that 12V USB supplies (i.e. 12V to 5V converters) vary wildly in performance. Some are not bad, some are downright awful. I had tried half a dozen or more supplies before finally finding a decent one. USB cables also vary a lot in their resistance, again from reasonable to dismal. Also, a shorter cable is always better, since every inch reduces the voltage seen by the device and there is very little to spare.
 
Version 4r1 does hace issues but i just saw 4r2 posted, maybe thats fixes the issues

That is very new, it wasn't there a few hours ago. Claims to fix some of the web socket updates, which sounds plausible.
 
Anybody know if it's possible to have enough power to light up everything but not have enough power to support the receiver?
Jim - did the red power LED on the Pi blink once in awhile? If so, its not getting the power needed and the first device to "brownout" are the USB connections (even though they may appear to be "lit"). Does the adapter you changed to have more than one socket? Sometimes the sockets have different power ratings.
 
Jim - did the red power LED on the Pi blink once in awhile? If so, its not getting the power needed and the first device to "brownout" are the USB connections (even though they may appear to be "lit"). Does the adapter you changed to have more than one socket? Sometimes the sockets have different power ratings.

Thanks, guys. Appreciate the responses. I discovered the issue in flight so my troubleshooting was limited to reboot/reconnect, but based on your feedback I am more suspicious than ever that my adapter was insufficient. Everything "looked" fine (ie lights were on) but I'd bet that my usb connections were indeed browning out due to lack of power.

I've been running an older version of the software simply because everything was working great. Will try to update to latest release as well.

Jim
 
Thanks, guys. Appreciate the responses. I discovered the issue in flight so my troubleshooting was limited to reboot/reconnect, but based on your feedback I am more suspicious than ever that my adapter was insufficient. Everything "looked" fine (ie lights were on) but I'd bet that my usb connections were indeed browning out due to lack of power.

I've been running an older version of the software simply because everything was working great. Will try to update to latest release as well.

Jim
I'd wait a bit before running the latest release unless you want to do some testing. The one released a few days ago has issues and there was a new release last night.
 
I started having reset problems even with a good power supply, especially in turbulence. My cord was unsupported that powered the pi, and I found that it doesn't take much vibration to get the red light to blink - and then the system resets.

I took a mini usb cord and made it "tight" by lifting the small metal tabs on the back side.

http://aramblinggeek.com/quick-fix-fixing-a-loose-micro-usb-cable

(These tabs aren't on all cables).

Then I put it back in the pi, and this time I tie-wrapped it securely so vibration won't affect it. Two test flights and it's rock solid.
 
Hi guys - I'm new to the forum, but I found this particular thread of great interest. I therefore took on the project this week. I've completed the sw load, assembled the hardware, and successfully completed the boot up. I have good power as I successfully connected the stratux from my ipad wifi and can see some weather on foreflight maps (note: only 1 dvr antenna & 1 edimax wifi usb connected).

My question is in regards to traffic. I went to devices within foreflight and expected to see "freeflight" listed as an available device. However, currently no devices are shown.

1. Where did I goof?

2. Is there a written procedure for this step in the process to enable traffic?

3. Is the issue related to lack of nearby towers... ie do I need to be near a tower for foreflight to show devices?

4. If that is the case, how am I getting weather shown on FF?

Any guidance provided will be greatly appreciated!
 
Just picked up the longer/thinner extended case version that Helio designed, I think I like it better that the shorter 3 piece case.

The short case can be a tight for space for USB cables.





http://3dhubs.refr.cc/3Q59NZS
 

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Hi guys - I'm new to the forum, but I found this particular thread of great interest. I therefore took on the project this week. I've completed the sw load, assembled the hardware, and successfully completed the boot up. I have good power as I successfully connected the stratux from my ipad wifi and can see some weather on foreflight maps (note: only 1 dvr antenna & 1 edimax wifi usb connected).

My question is in regards to traffic. I went to devices within foreflight and expected to see "freeflight" listed as an available device. However, currently no devices are shown.

1. Where did I goof?

2. Is there a written procedure for this step in the process to enable traffic?

3. Is the issue related to lack of nearby towers... ie do I need to be near a tower for foreflight to show devices?

4. If that is the case, how am I getting weather shown on FF?

Any guidance provided will be greatly appreciated!

Which software version did you download? There is a issue with the version released before last night (0.4r1) in that it is slow to make a wifi connection, and it drops off even if a connection is made. I don't know if it has been fixed in 0.4r2 which was released last night.

There is some information in this link: https://github.com/ssokol/stratux/wiki/Stratux-Beginner's-Guide

Verify with the web interface that the unit is talking.

There is an icon that looks like a gear in the upper left of ForeFlight (iPad)- poke around there, if the Stratux is found, you can enable traffic.
 
Which software version did you download? There is a issue with the version released before last night (0.4r1) in that it is slow to make a wifi connection, and it drops off even if a connection is made. I don't know if it has been fixed in 0.4r2 which was released last night.

There is some information in this link: https://github.com/ssokol/stratux/wiki/Stratux-Beginner's-Guide

Verify with the web interface that the unit is talking.

There is an icon that looks like a gear in the upper left of ForeFlight (iPad)- poke around there, if the Stratux is found, you can enable traffic.

Cap'n Jack - thanks for the advice. I loaded v0.4r2 as recommended. It connected via wifi to the ipad without issues. Additionally I confirmed the connection status via the IP address 192.168.10.1 as referenced in the Beginner's Guide but no message count yet (12min since opening page).

In ForeFlight, I do not see a choice under the "Devices" option (empty field). Devices is found under the "More" tab at bottom right.

Additionally, under "Maps" tab (second from the left on bottom) I see no clear reference under the gear symbol (found at top left) or any choice for traffic under the top leftmost pull down option.

Is it time to drive around for a tower? Or is there something additional in the setup to try out? I am a true newbie at this so all guidance will be greatly appreciated.
 
Cap'n Jack - thanks for the advice. I loaded v0.4r2 as recommended. It connected via wifi to the ipad without issues. Additionally I confirmed the connection status via the IP address 192.168.10.1 as referenced in the Beginner's Guide but no message count yet (12min since opening page).

In ForeFlight, I do not see a choice under the "Devices" option (empty field). Devices is found under the "More" tab at bottom right.

Additionally, under "Maps" tab (second from the left on bottom) I see no clear reference under the gear symbol (found at top left) or any choice for traffic under the top leftmost pull down option.

Is it time to drive around for a tower? Or is there something additional in the setup to try out? I am a true newbie at this so all guidance will be greatly appreciated.

Thanks for your patience with me. I was going from memory for ForeFlight. To the left of the gear thing, you can select which charts are displayed. This also allows you to select the overlays, traffic is one of the overlays.

From your ipad, you can open a web browser and enter http://192.168.10.1 and you should see a web page from the Stratux. Use "Menu" and you can figure out how to turn on the 1090es receiver- this configures this receiver and you should only need to do it once after you install software. The beginners guide I linked to earlier has more information. If there are commercial planes nearby, you should see them. I'm told the 978 really only works once your are flying.

Release 2 is much better, though it seems to take a long time to connect to Wifi.
 
Not really. Not unless you provide the measurements for your hand. The details on the website don't provide the dimensions, either.

There's plenty of free stl file viewers, download one and open the projects. They'll have dimensions. I believe this one is like 167mm
 
I'd wait a bit before running the latest release unless you want to do some testing. The one released a few days ago has issues and there was a new release last night.

I find that if the replay logs are switched on, there are heartbeat issues, oblivious all that data it collects is cached for a while in memory then flushed to thr SD card, resulting in lost of heartbeat. Switch replay off and nomlost of connects etc.
 
There's plenty of free stl file viewers, download one and open the projects. They'll have dimensions. I believe this one is like 167mm

STL Viewer - marvelous concept! I was expecting to need AutoCAD....

thanks!
 
Thanks for your patience with me. I was going from memory for ForeFlight. To the left of the gear thing, you can select which charts are displayed. This also allows you to select the overlays, traffic is one of the overlays.

From your ipad, you can open a web browser and enter http://192.168.10.1 and you should see a web page from the Stratux. Use "Menu" and you can figure out how to turn on the 1090es receiver- this configures this receiver and you should only need to do it once after you install software. The beginners guide I linked to earlier has more information. If there are commercial planes nearby, you should see them. I'm told the 978 really only works once your are flying.

Release 2 is much better, though it seems to take a long time to connect to Wifi.

Cape jack - thx again for the feedback. Still no joy. The drop down you mentioned does not have an option for traffic in FF. I did open the recommended website, opened the menu and activated both uat and 1090 but no change in FF. Same conditions remain as previous post.

Has anyone else on the forum had this issue?
 
I notice that at least one guy on reddit is saying his single antenna dual band solution has no performance degradation. I really hate the idea of two antennas, so would greatly prefer to avoid it. Does anyone here have any experience with that? (I know antenna gurus cringe at the thought, but I prefer practical to perfect.)
 
I notice that at least one guy on reddit is saying his single antenna dual band solution has no performance degradation. I really hate the idea of two antennas, so would greatly prefer to avoid it. Does anyone here have any experience with that? (I know antenna gurus cringe at the thought, but I prefer practical to perfect.)
I've wondered too, been waiting on Weird Jim to comment. He knows this stuff pretty well.
 
Thanks for your patience with me. I was going from memory for ForeFlight. To the left of the gear thing, you can select which charts are displayed. This also allows you to select the overlays, traffic is one of the overlays.

From your ipad, you can open a web browser and enter http://192.168.10.1 and you should see a web page from the Stratux. Use "Menu" and you can figure out how to turn on the 1090es receiver- this configures this receiver and you should only need to do it once after you install software. The beginners guide I linked to earlier has more information. If there are commercial planes nearby, you should see them. I'm told the 978 really only works once your are flying.

Release 2 is much better, though it seems to take a long time to connect to Wifi.

Cap'n Jack - thank you for taking the time to help me out. I confirmed via the ip address and activated both uat and 1090 (though I only have 1 antenna). Sadly, still no counts on the status page of the iPhone address.

Checking back in ForeFlight, still no traffic overlay is available to choose from. Additionally, no devices are shown either. I remain in the same state of condition as my prior post.

Are there other on the forum that have been able to confirm funtionallitywith traffic on ForeFlight? If so, what did you do different?

Thanks for your patience.
 
I've wondered too, been waiting on Weird Jim to comment. He knows this stuff pretty well.

OK, so you all need to understand just a little bit of how this stuff works ...

The geometric mean frequency is the geometric center of 1090 (Fh) and 978 Fl), which is given by sqrt(1090*978) = 1032 MHz. = Fc

The % bandwidth we need to cover is given by (Fh-Fl)/Fc =(1090-978)/1032 = 15.3%

Now it is the "fatness" of the antenna that gives us % bandwidth. That is, the wider the antenna for it's length the greater bandwidth it will cover. The APPROXIMATION of bandwidth goes something like this:
The antenna length (inches) for a quarter-wave antenna at 1032 MHz. is given by L = 2950 / Fc = 2.86 inches.

The ASPECT ratio of an antenna is pretty much the same thing for airplanes as it is antennas. The LENGTH (wing length) divided by the WIDTH (chord) is the aspect ratio. If we use good old easy to come by 1/2" copper tape (or aluminum foil, or brass, or aluminum, or ...) then the aspect ratio is 2.86 / 0.5 = 5.71

The bandwidth in MHz. (a purely subjective, yet remarkably useful term) is given by (Fc * 6) / aspect ratio, = (1032 * 6) / 5.71 = 1084 MHz.

Hmmm ... that is WAY overkill, so let's see what happens if we drop the antenna width down to an eighth-inch (0.125") rod.

Aspect ratio now increases to 22.9, and bandwidth drops to 270 MHz., or a % bandwidth of 270/1032, or 26%. WAY more than we need, but certainly a practical way to build the antenna.

Dropping the rod diameter down to one-sixteenth of an inch drops the % bandwidth down to 13%, which is somewhat LESS than what we need.

So, after all this malarkey we find that a 1-eighth" diameter rod is more than what we need (but certainly useable) and a 1-sixteeenth" diameter rod is less than what we need. If you would like to convert these to WIRE sizes (a very convenient way of making a short antenna) these correspond to #8 and #14 respectively. #12 or #10 stripped Romex may be a very good compromise.

Note that whether you use a circular rod or a very thin tape, it is the WIDTH of the rod or tape that makes the difference. It makes VERY LITTLE difference whether you use rod or tape, the performance will be the same.

Now the fine tuning. Any increase in wire diameter from infinitely small (impossible) to any width whatsoever shortens the antenna. You start at 95% of theoretical and as you get fatter and fatter, the antenna shrinks and shrinks in length. How much? That's what they make antenna impedance meters and wirecutters for. If I were to make a best guess, I'd go with about a 92% foreshortening of the antenna for the #12/10 wires above giving the antenna the following final dimensions:

Length of antenna (total above the ground plane) of 2.86" * 92%, or a best first guess of antenna length = 2.63"

Diameter of antenna somewhere between 0.125" and 0.062"


Did that help somewhat?

Thanks,

Jim
 
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Thanks for your patience with me. I was going from memory for ForeFlight. To the left of the gear thing, you can select which charts are displayed. This also allows you to select the overlays, traffic is one of the overlays.

From your ipad, you can open a web browser and enter http://192.168.10.1 and you should see a web page from the Stratux. Use "Menu" and you can figure out how to turn on the 1090es receiver- this configures this receiver and you should only need to do it once after you install software. The beginners guide I linked to earlier has more information. If there are commercial planes nearby, you should see them. I'm told the 978 really only works once your are flying.

Release 2 is much better, though it seems to take a long time to connect to Wifi.

Capn Jack - I've gone through the IP address setup menu and cecked both uat and 1090. Still no joy. I've read and tried all items described on the Beginner's Guide.

In Foreflight, I checked the drop down menu for the traffic overlay and it is not available as a choice (does not appear at all). I remain in the same condition as my previous post.

Has someone from the forum been able to obtian traffic with Foreflight. If so, is there something I missed?

Thanks for the help.
 
Jim - that was fantastic - but to the original question - and apologies if I missed the answer :) ...

2 SDR's (978 & 1090) combined into one external antenna per this photo. This does not impact reception of either frequency?
 

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It will work but a couple of things to keep in mind:
There will be a loss of 3 dB (half the signal strength) through the T. This will decrease the received signal strength at the SSR dongles. However, depending on how the EFB determines the target range it may not be noticeable to the end user.

Also, without impedance matching at the T, the coax lenghts and losses should be kept symmetrical between each dongle and the T. Impedance mismatch and differences in coax lengths can cause phase cancellation of the desired signal thus further reducing the signal delivered the respective dongle.
 
It will work but a couple of things to keep in mind:
There will be a loss of 3 dB (half the signal strength) through the T. This will decrease the received signal strength at the SSR dongles. However, depending on how the EFB determines the target range it may not be noticeable to the end user.

Also, without impedance matching at the T, the coax lenghts and losses should be kept symmetrical between each dongle and the T. Impedance mismatch and differences in coax lengths can cause phase cancellation of the desired signal thus further reducing the signal delivered the respective dongle.
This, I understand. Thank you for the clarification of Jim's abundant knowledge.

Sent from my SM-G900T using Tapatalk
 
It will work but a couple of things to keep in mind:
There will be a loss of 3 dB (half the signal strength) through the T. This will decrease the received signal strength at the SSR dongles. However, depending on how the EFB determines the target range it may not be noticeable to the end user.

Also, without impedance matching at the T, the coax lenghts and losses should be kept symmetrical between each dongle and the T. Impedance mismatch and differences in coax lengths can cause phase cancellation of the desired signal thus further reducing the signal delivered the respective dongle.

To elaborate on this ...

The odds of using a single T (like a BNC tee) and getting decent performance lie somewhere between winning and argument with your wife and winning an argument with an umpire.

The problem is that frequencies around 1 GHz. (which is where we are operating) are too LOW for decent microwave techniques and too HIGH for decent coaxial cable or ferrite techniques. Making an isolated splitter at these frequencies is a real trick. Let me go back and do some research ... seems to me that some notes I packed away some years ago had some cleverness in them. Back to you all later this afternoon.

Jim
 
OK, here is the deal. I went back and found an obscure footnote to a design note that I got back in the late 1960s that said that a popular style of antenna splitter ("Wilkinson splitter", google at your peril) was good not only at the frequency for which it was designed, but at 3x the frequency, 5x the frequency and so on for all odd multiples of the frequency.

That led me to think that if we design a good splitter down at 343 MHz. it will also be good at our center frequency of 1035 MHz. I don't know that this is true, but I see no reason that it should NOT be true. Designing down at 300 MHz. is a deuce of a lot easier than at 1 GHz.

I know for a fact that this splitter design is VERY wide band; I've used it for YEARS down at the VHF nav band to split the VOR/LOC signal (108-118 MHz.) to two nav receivers and have tested it for equal split and "isolation" from about 80 MHz. to 150 MHz. and it is still "good" (a subjective term).

"Isolation" means that if you do something at one of the receiver ports, how much does that affect the other receiver port? The answer (once again subjective) is that you can short the #1 receiver port, you can open the #1 receiver port, and any combination in between and have VERY LITTLE effect on what happens at the #2 port.

And, the center frequency of the splitter is dependent on one thing and one thing only ... the lengths of two pieces of coax.

So, here is the deal. I will supply ONE of you with the parts to build said splitter. Free. You have to assure me that you have worked with RF and VHF at least (microwave preferred) and that you understand that a quarter of an inch difference or long leads more than a few tenths of an inch long will completely cob up the circuit. You have to be comfy with me being a real prick about construction techniques that I lay out.

Having said all that, somebody volunteer and I'll give you my mailing address by email so that you can send me a self-addressed stamped envelope. What you will get back is coax cable, BNC connectors, a piece of PC board for construction and some rather detailed instructions. What I want back and posted on this group are pictures of what you made and subjective comments on how well it worked.

Once we prove that it worked and worked well, we can then proceed to making it smaller and easier to construct. But the breadboard has to be full-size without any shortcuts to prove the basic point.

Any takers?

Jim
 
I need help. I've confirmed connection to ipad via wifi with stratux. I setup the configuration page via the ip address to 1090. However, I cannot see a connection within ForeFlight that shows the Stratux device connected. Therefore do not have the traffic overlay option displayed. Has anyone been through this scenario? I have loaded v4r2.
 
OK, here is the deal. I went back and found an obscure footnote to a design note that I got back in the late 1960s that said that a popular style of antenna splitter ("Wilkinson splitter", google at your peril) was good not only at the frequency for which it was designed, but at 3x the frequency, 5x the frequency and so on for all odd multiples of the frequency.

That led me to think that if we design a good splitter down at 343 MHz. it will also be good at our center frequency of 1035 MHz. I don't know that this is true, but I see no reason that it should NOT be true. Designing down at 300 MHz. is a deuce of a lot easier than at 1 GHz.

I know for a fact that this splitter design is VERY wide band; I've used it for YEARS down at the VHF nav band to split the VOR/LOC signal (108-118 MHz.) to two nav receivers and have tested it for equal split and "isolation" from about 80 MHz. to 150 MHz. and it is still "good" (a subjective term).

"Isolation" means that if you do something at one of the receiver ports, how much does that affect the other receiver port? The answer (once again subjective) is that you can short the #1 receiver port, you can open the #1 receiver port, and any combination in between and have VERY LITTLE effect on what happens at the #2 port.

And, the center frequency of the splitter is dependent on one thing and one thing only ... the lengths of two pieces of coax.

So, here is the deal. I will supply ONE of you with the parts to build said splitter. Free. You have to assure me that you have worked with RF and VHF at least (microwave preferred) and that you understand that a quarter of an inch difference or long leads more than a few tenths of an inch long will completely cob up the circuit. You have to be comfy with me being a real prick about construction techniques that I lay out.

Having said all that, somebody volunteer and I'll give you my mailing address by email so that you can send me a self-addressed stamped envelope. What you will get back is coax cable, BNC connectors, a piece of PC board for construction and some rather detailed instructions. What I want back and posted on this group are pictures of what you made and subjective comments on how well it worked.

Once we prove that it worked and worked well, we can then proceed to making it smaller and easier to construct. But the breadboard has to be full-size without any shortcuts to prove the basic point.

Any takers?

Jim


I have that ability but don't have any interest in bothering with worrying about if a prototype quality device has one or two antennas. :)
 
Another option, if you want to keep the impedances and isolations constant, is a good quality Cable TV splitter. These have fairly constant losses (around 3 dB to 4 dB) and impedances up through 1000 MHz. However, they start getting lossy above 1100 MHz and I don't know how fast they roll off. This may not be an issue as the 1090 ES transponders will be airborne and in the same vicinity as the Own Aircraft and thus would have stronger received signals than the 978 UAT tower signals.

After a quick internet search, here are the specs I found on one such splitter:
http://www.legrand.us/onq/networking/coax-networks/adapters-and-splitters/vm2202-v1.aspx

The F connectors on the splitter will need to be adapted to the MCX connectors on the RTL-SDR dongles. Here is one such cable for the splitter to dongle connection:
http://www.amazon.com/coaxial-cable-female-right-angle/dp/B00CKG6T9I

This will also require 2 F Type Male to F Type Male adaptors to "gender change" the connections. For example:
http://www.amazon.com/OHM-Coaxial-Type-Male-Adapter/dp/B000ASFZXO

Looking at a version of the datasheet, the dongles appear to be 75 ohm devices. This makes sense as they were designed to be inexpensive TV receiver tuners. As such, no impedance matching would be needed between the 75 ohm splitter and the 75 ohm dongle if using 70 / 75 ohm cable. If a 50 ohm antenna is used, a matching section could be inserted between the splitter and antenna. Following Jim's discussion on the antenna, a 60 ohm quarter wave line at 1032 MHz (the geometric mean between 978 MHZ and 1090 MHz) would go between the antenna and splitter to transform the 50 ohm antenna impedance to the 75 ohm splitter impedance. But in practice, it may not be worth the effort.

Anyway, just some thoughts on another way to address the issue of using one antenna.
 
Another option, if you want to keep the impedances and isolations constant, is a good quality Cable TV splitter.

.............

Anyway, just some thoughts on another way to address the issue of using one antenna.

there were (are) splitters available for home satellite TV that have the requisite frequency range and loss characteristics at a very reasonable price. I think some cable splitters may work, but the ones that go inline between the LNB and the receiver on a satellite system ought to work as they operate in the 900-215o range. They use F connecters, which should work with a simple quarter-wave antenna made from RG-6. You'll need an adapter to go between the splitter and the dongle, but those are readily available on Amazon or Fleabay.

The satellite splitters SHOULD work, but I've not tried one yet. Satellite inline cable amplifiers do work, though.
 
Here's my dual band receiver. I got a $0.98 plastic box at wallyworld

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