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Radio Direction Finding Forum - Discussions regarding direction finding and transmitter location

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Old 07-19-2018, 4:14 PM
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Default Putting together a receiver but have questions

Hi,
Questions first if you don't want to read the rest:
Can hand scanners like the BaoFeng UV-5RA or similar 'listen' to 216-224mhz?
Can a hand scanner like this be used for locating (with a suitable antenna)?
Do you think the scanner can locate the transmitters from https://www.com-spec.com and others go from 216 to 224.970mhz.
I'm hoping the scanner would be narrow-banded enough to discriminate the specific channels these transmitters come in.


I fly remote control gliders and recently had one get lost in a corn field. One of the club members had a drone and we found my ;lane the next day.
I must have walked past it several times while looking for it but only when the drone was directly above it could I find it. You'd think a 4meter white and red plane would be easy to see. I didn't see it till I was 5feet from it.

Anyway, the club just got this tracking system:
RC PLANE, Communications Specialists Inc., RC Plane, Model Airplane Tracking, Model Rocketry Tracking, ELT
However, I live in a different state than the club and would like to come up with a receiver on my own to work with their transmitters.
They are on 216-224mhz.
I think I can use a hand scanner like the Realistic Pro94 (with the proper antenna) to find them, right?

I'm finding that most of the scanners don't include the 216-224mhz band. Can scanners that don't include that band 'listen' on those frequencies?
I've found several statements that seem to indicate the scanners can transmit on specific bands but receive on frequencies outside of the ones listed.

Would anyone have a recommendation on what to use for a receiver for these transmitters?
http://www.com-spec.com/rcplane/manu..._HP_Manual.pdf

Any help to get me pointed in the right direction would be appreciated.
Thanks,
davidk
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Old 07-19-2018, 7:35 PM
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The R-300A receiver used with these transmitters states its mode of operation is SSB/CW which is not supported by the Baofeng transceiver. A few scanners can receive these modes however they are more expensive than typical scanners.

If you can find a scanner that receives AM mode in that frequency range, you might be capable of receiving the signal however with likely a lot less sensitivity than the actual receiver made to find the tracking device.

Shawn
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Old 07-19-2018, 9:19 PM
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Thanks for the quick reply.
I wasn't aware those modes weren't widely supported or something I needed more info on. I'll do some more searching.

If I can find a scanner cheap enough in case it doesn't work, I might get enough range to be helpful. Usually my planes haven't been too far away or in an unknown direction that even limited range wouldn't help.
Many guys use beepers, and that could have worked for the corn, but an RF tracker has a coolness factor. Besides, it should be a fun project.
Here's what I was up against. https://youtu.be/TTtnlixMI5k
I knew it was straight off the end of the runway but even six people walking the rows didn't find it.

I'd like to use the beacons from the links but I'm really only flying with the club about 12 times a year. If I can put together my own system with a more diy-friendly frequency/modes I'd be good with that. Range doesn't need to be more than a 1/2 mile I'd guess.

Thanks again for the info.
davidk
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Old 07-20-2018, 5:21 AM
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Quote:
Originally Posted by davekra View Post
Hi,
Questions first if you don't want to read the rest:
Can hand scanners like the BaoFeng UV-5RA or similar 'listen' to 216-224mhz?
Can a hand scanner like this be used for locating (with a suitable antenna)?
Do you think the scanner can locate the transmitters from https://www.com-spec.com and others go from 216 to 224.970mhz.
I'm hoping the scanner would be narrow-banded enough to discriminate the specific channels these transmitters come in.


I fly remote control gliders and recently had one get lost in a corn field. One of the club members had a drone and we found my ;lane the next day.
I must have walked past it several times while looking for it but only when the drone was directly above it could I find it. You'd think a 4meter white and red plane would be easy to see. I didn't see it till I was 5feet from it.

Anyway, the club just got this tracking system:
RC PLANE, Communications Specialists Inc., RC Plane, Model Airplane Tracking, Model Rocketry Tracking, ELT
However, I live in a different state than the club and would like to come up with a receiver on my own to work with their transmitters.
They are on 216-224mhz.
I think I can use a hand scanner like the Realistic Pro94 (with the proper antenna) to find them, right?

I'm finding that most of the scanners don't include the 216-224mhz band. Can scanners that don't include that band 'listen' on those frequencies?
I've found several statements that seem to indicate the scanners can transmit on specific bands but receive on frequencies outside of the ones listed.

Would anyone have a recommendation on what to use for a receiver for these transmitters?
http://www.com-spec.com/rcplane/manu..._HP_Manual.pdf

Any help to get me pointed in the right direction would be appreciated.
Thanks,
davidk
In addition to what has already been mentioned, a scanner is not going to have the differential receive, to let you know whether the signal is coming the right or the left.

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Old 07-20-2018, 6:58 AM
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Thanks Krokus,
I was thinking I could replace the whip antenna? that comes on the scanner with a Moxon (like the commercial unit) or a yagi.
The antennas are replaceable, right? That combined with the squelch might work?

I hope to spend more time than money on this. I mean, in the end I'd like to have something that works (albeit, not as well as the store bought one) at considerably less cost than the commercial system so I can say 'I made this".
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Old 07-20-2018, 10:43 AM
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Quote:
Originally Posted by davekra View Post
Would anyone have a recommendation on what to use for a receiver for these transmitters?
http://www.com-spec.com/rcplane/manu..._HP_Manual.pdf

Any help to get me pointed in the right direction would be appreciated.
Thanks,
davidk
Check on e-bay for wildlife tracking receivers. These frequencies are used for that, and there are occasionally purpose built receivers that will cover these bands.
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Old 07-23-2018, 12:37 AM
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Quote:
Originally Posted by davekra View Post
Thanks Krokus,
I was thinking I could replace the whip antenna? that comes on the scanner with a Moxon (like the commercial unit) or a yagi.
A Yagi would give you directional receive, as long as you have one for the frequencies. That would allow you to triangulate a source. Look at pages about Fox Hunting, for some of the techniques used. (As a bonus, with 1.25m, the antennas are easily handheld.)

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Old 07-23-2018, 6:16 AM
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Thanks, I've been scanning pages on calculating the dimensions of various antennas.
The one I'm leaning towards uses a tape measure for the elements. Having no formal training in RF circuitry some of it seems like black magic.
For instance, on a Yagi, you have the driven element. It needs to be the correct length, I get that because the waves are of a certain size and you want it to be in phase. Then there's a loop of wire connecting the two and it needs to be sized correctly as well. But electrically is simply shorts the two elements. Also, I don't really understand how the other elements direct energy to the driven element.

In the end I'll just go by what the calculators say and what others have done.

On a side note, I just picked up an RTL-SDR dongle for $20. Pretty impressive for that money.
With the antennas included it seems pretty quiet around me. Kinda strange considering I'm in a relatively big city (Milwaukee). I was able to hear a transmitter I built using the cheap 433mhz modules I had lying around.
I'm going to build a Yagi for 433mhz to see if the SDR will allow me to track before buying one of the transmitters I linked to earlier.
If I can create a tracker using my phone and the SDR I would be happy.

Thanks for all the help and suggestions.
davidk
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Old 07-23-2018, 4:07 PM
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To pinpoint a nearby signal source, a simple TDOA antenna setup is very effective. Circuit and antenna are easy to build. Solid copper house wiring (with the insulation left on) is easy to work with to make the antenna elements. Dimensions are NOT critical. Lots of info on the Google. Here's a sample: A TDOA Antenna Unit for Fox-Hunting
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Old 07-28-2018, 6:18 PM
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Thanks Slicerwizard,
That schematic looks far simpler than what I'd found earlier. What I was finding all had a microcontroller or GPS functions.

I built the circuit and antenna and played with it for a couple days. I used the 433mhz ASK transmitter module with a 555 driving it with around 1khz. I can hear that tone coming from the SDR hooked to the antenna but can't hear the tdoa tone. From what I've read, I'm not sure the transmitter is appropriate for this but I thought the Tx could be almost anything but the Rx needed to be FM.

One of the TDOA sites says it's not good for a pulsed Tx. The Com-Spec Tx modules are pulsed for 25ms at about 50hz.

I ordered and received one of the transmitters from Com-Spec. It's a nice unit. A gold cup, hermetically sealed by the circuit board. It drops into the plastic piece and uses one battery. It's a little bigger than a quarter and about .5" thick. A screw terminal on the outside secures the antenna.
It looks like they are programmed after they are assembled. Kinda wish I could see what they're using. I'd found some Tx chips that can be programmed for specific frequencies that might work...Still, at $50 for a guaranteed working Tx it's not so bad.

The Rx on the other hand at around $300 for the cheapest...I think I've got something working using the SDR and my phone. I mocked up a Moxon antenna using #14 wire and foamcore board. Initially I wasn't able to determine direction but then I added an attenuator and got reliable results.
Given that success, I ordered a step attenuator from ebay. Do a search for PE4302. I'll use an arduino and rotary encoder to adjust it. No display, just not needed for this application.
Unfortunately it's coming from China so I'm stuck for a bit till it gets here. I'll work on a more robust and collapsible antenna and phone holder. I think the handle will hold a battery and SDR.

What do you think going the SDR/phone route? A little fiddly but should get the job done.
Thanks for listening.
davidk
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Old 08-14-2018, 10:46 PM
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"Please forgive the crudity of this model. I didn't have time to build it to scale or paint it." Doc Brown.

I took the attenuator evaluation board I received and cut it down to fit on the end of the SDR and moved the SMA connector to it. It's slid into the case with a piece of pcb separating it from the other components.
An Arduino ProMini, rotary encoder, speaker and a buck/boost regulator. The rotary encoder beeps when it reaches the upper and lower limits.

I've not tested it in this final form but was getting acceptable results with everything connected without a case. Even without an antenna I was getting a strong signal so I'm hoping being fully shielded will help with that.
I also bought an offset attenuator kit from 3rd Planet Solar, https://kc9on.com/ . For $11 shipped it's cheap and I'm not scrounging for parts. If after testing I find it works well, is there a way to have both it and the step attenuator and switch them in and out of the circuit?

I've been researching antennas and have some designs to try. One that looks interesting (I don't know the name) has two 1/4wave dipoles separated by a 1/4wave and one side has a 1/2wave length of coax. It's supposed to have a very deep null.

I'm open if anyone has any suggestions on any part of this project.
Thanks for looking.
davidk
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Old Yesterday, 11:42 PM
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The shielding works! Can still hear the signal without an antenna when you're real close, but get 5' away and it almost disappears.

I've added the offset attenuator and did a quick test. Offset is the way to go. You eliminate the signal leaking in and can focus on making a good antenna.

I wanted to control the offset attenuator with the same encoder used for the step attenuator. Use the button on the encoder to switch from one to the other, then use a digital potentiometer instead of analog pots.
Discussing it with John at 3rd Planet, the digital pot may not be able to handle the frequency and simply pass through the chip.
I had to relocate a few things inside the box but it all fits. The controls are a little close together but it's not too bad.
A short coax jumper will connect the offset attenuator into the circuit.
Just need to build a handle and antenna mount and we can start RDFing.

davidk
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