BC346XT: Struggling with BC346XT--model rocket locator

[schneijt]

Hi all,

I'm not experienced at all with scanner receivers and/or radios in general, so forgive me if what I'm about to ask ends up being really stupid on my part. I also apologize in advance for the length of this post--I'm going to go as detailed as I can, since I know that might help someone figure out if my scanner isn't working right, or if I'm just an idiot who is missing something really simple that I should have figured out on my own.

I fly rockets, and my local club flies on farm land. Needless to say, rockets and corn fields don't mix well. At a national sport launch a few weeks ago, I bought a rocket tracking system (minus receiver) from a guy who was getting out of the hobby. It's a small transmitter that transmits on 219.5267 MHz, and using a yagi-style directional antenna (which is labeled as optimized for 218-220MHz spectrum), you connecting it using a BNC cable into the adapter on the scanner hone in on the direction of your rocket so you can walk a straight line to it and course correct as you get closer and closer to the landing spot of the rocket. He demonstrated it using his $400 Radio Shack scanner that he wasn't selling, and I bought the transmitter and antenna.

Looking to not spend $400 on a scanner to use a transmitter and antenna that I bought for $80, I bought a refurbished BC346XT on Amazon. The issue I'm having is that, unless I'm an idiot and I'm missing something, I don't think the antenna connection on my unit is working correct. With the stock antenna, it picks up the signal in every direction, as expected. However, with the directional antenna connected, it still picks up the signal in every direction. Removing the antenna entirely, I discovered that if I walked just far enough away to lose the signal, I could touch my fingers (or any piece of metal at all) to the threads for connecting an antenna, and the signal would be picked up. It seems like the antenna connection is not functioning properly. Obviously, with the direction antenna attached and the scanner using the antenna correctly, it would only pick up the signal when I have the yagi antenna pointed in the direction of the transmitter. Since it picks up all FM radio signals and everything else I've scanned for, I know the scanner works when it receives the signal, but it's just a matter of me figuring out how to get it to be directional instead of picking up in every single direction around me. It just seems that the directional antenna isn't directional at all, and the fault seems to lie with the antenna connection on the BC346XT unless I'm missing something. I tried attenuating on the scanner and everything else I could think of and play around with, but I can't figure out how to connect the directional antenna and actually have it only pick up the signal in one direction properly.

Has anyone had trouble connecting a yagi style directional antenna to the BC346XT? I'll never find a rocket in the corn fields using my system if it says there's a signal in every direction, lol. I'm wondering if I need to return the refurbished scanner and try again with a different unit or a different model because it's possibly defective.

Thank you all for your time and help; I appreciate it!
Joe S.

 

[Mike_G_D]

As far as I can tell, your not doing anything "wrong" per se except maybe not taking the strength of the transmitter into account and the characteristics of the Yagi.

Firstly, yes, your finger and any piece of metal will act as an antenna - maybe not as efficient as a true tuned antenna for the desired frequency but still an antenna of sorts. What you experienced is not unusual.


As to Yagi's - I don't know about yours in particular but different Yagi antennas have different characteristics - they are not all created equal. How many elements does your yagi have (the metal elements perpendicular to the boom)? In general, the more elements it has the more directional it will be. With only three elements it won't be as directional as say one with six or eight elements. Also, just because an antenna is directional does not mean it won't pick up signals from other directions besides the one it is aimed at - that's one of the characteristics you need to pay attention to. All will have some response even towards the completely opposite end from where you are aiming it. With a strong enough signal, you may not be able to tell where the right direction is due to how strong the signal is.

What I would do is connect the Yagi to the scanner, activate the transmitter and walk away as far as you can and still hear the signal on the scanner - just before it fades badly. I am guessing the transmitter is not that strong but I don't know exactly, of course. Is there a power rating on the transmitter (like 1/4 watt, 100miliwatts, etc. or at least a FCC Part 15 label)?

When you get to a point where the signal is coming in weakly but readable, then try aiming the antenna. Try both vertical and horizontal polarizations (vertical means the elements are pointing up and down relative to the horizontal boom and horizontal means they are pointing left and right) whichever works best (or worse if you need to attenuate the signal when you get so close the antenna directionality is compromised). You should now be able to aim the antenna and definitely see a signal difference depending on direction.

I think you were testing it too close to the transmitter so that the antenna's directional characteristics were not good enough to see a difference.

Also, how are you determining signal strength? Are you using the 346's signal meter? That's not all that good but better than nothing. Listening to the quality of the signal alone is not all that good either. You kind of have to do both and practice a lot.

This is called RDF or Radio Direction Finding. It is a science and art all unto itself! There are many in the Amateur Radio hobby that concentrate on this aspect quite intensely. I would STRONGLY suggest that you see if you can contact a local Ham Radio club in your area and see if they have an active RDF team or group. If so, they can really help you out in this! And they would probably be more than happy to do so. You might even take an interest yourself, who knows?! Anyway, you might start by asking this same question in the Radio Direction Finding sub forum on this site: Radio Direction Finding Forum - The RadioReference.com Forums. The folks there may help you far more than I can!

In short, I think your equipment is ok - maybe not the best for what you are trying to do but operating correctly anyway. Try looking up a local ham radio direction finding (also called "fox hunting") group and seeing if you can enlist their expertise and help. Also try asking in the Radio Direction Finding forum on this site. And finally, on your own, make sure you are hearing a weak but readable signal first before testing the directionality of your antenna - too strong a signal and it won't work well (directionality-wise).

-Mike

 

[schneijt]

Thanks, Mike, that was quite helpful. There are only three elements on the antenna, so that explains part of the reason it wasn't as accurate as I was hoping it would be. I've only tried walking a couple hundred feet away from the transmitter, so I will definitely try a much longer distance; I guess I was expecting more out of this system than was reasonable given the setup. As far as the power of the transmitter, I don't know. There aren't any markings on the plastic housing or the electronics tray that slides into it after the battery is inserted. All the trackers we use from different companies for rocket locating all have a range of a few miles as long as it is an unobstructed path, so I don't think the signals being broadcast are terribly strong. Regarding signal strength, I only have the readout on the scanner to go by, which I figured wasn't super accurate but was good enough. I know the really expensive receivers that some rocket locator systems use have "ranges" you can select that will help the receiver adjust to the signal the further away and then closer you get to the source of the signal. I'm sure it would help if I were able to adjust the attenuation or receiving strength of the scanner, which I don't think I'm able to do with my scanner. At the end of the day, I clearly have a lot of playing around with this setup to do so I can find the maximum usefulness for my use. It also sounds like I would benefit greatly from someday upgrading to a "fancier" model of receiver/scanner.

Thanks again!
Joe

 

[phask]

RDF for Hams is called Fox hunting. I used to do it quite a lot.

The main issue, at least I think it is, the signal is too strong. or the scanner has limited shielding. If too strong you can add an inline attenuator - sort of like a volume control. Similar to this ATT-20 Variable Attenuator

There are many and you should not need one that expensive.

The scanner may also have a attenuator that has a choice of on/off. Not familiar at all with that scanner.

While a 3 element is not the greatest , it should be adequate. I built a 3 element, then later went to 5 or 7.

Antenna building is ANOTHER hobby

FWIW - hunters with high priced hounds use a similar system - not sure of the frequency or the power, but they track the dogs for a mile plus.

Suggestions - practice

Maybe try a different receiver if you can borrow one.

 

[Mike_G_D]

I honestly think you could benefit most from contacting some folks really into radio direction finding - more so that than getting a fancier scanner! Most scanners don't make great RDF receivers by themselves without modification or ancillary accessories like a Doppler unit. Look here for an example of such a beast (which could be used with your scanner, theoretically): Ramsey Doppler Direction Finder Kit : Amateur Radio Gear.

I'd really ask in the Radio Direction Finding forum and see if you can find any folks close by you who are into this - it could wind up saving you a lot of time and money!

-Mike

 

[Mike_G_D]

What phask posted (variable attenuator) makes more sense for foot use than what I posted (doppler unit). The latter is obviously intended to be mounted in and on a car and is good for initial location when mobile in a car (if what you're looking for is a long distance away) but for closer in walking distance using a variable attenuator as phask suggested is more appropriate, not to mention cheaper! To use, simply keep increasing the attenuation on the variable attenuator as you get closer and closer so as to reduce the signal level such that the antenna can better utilize its directional characteristics.

As I said - I'm no RDF expert, that's why you should look for some; don't rush out and buy a fancier scanner (the 346 is actually a pretty fancy analog trunk tracking scanner and getting it for $80 was a good deal!)!! I don't think fancier scanners will help you as much as practice and better and more appropriate knowledge, which, again, can be obtained from those more into RDF - phask is a case in point! If you're going to put more money into it then I would opt for focusing on the antenna as well as that variable attenuator and not the scanner itself.

-Mike

 

[JamesO]

A few things, are you using the directional Yagi in the proper orientation?

Make sure you are not using the antenna backwards. Many times the reflective element is the longest element.

Also even a directional antenna has a wide beam and it is often hard to get an idea of the signal location due to the wide beamwidth.

Many times finding the Null signal is much more accurate and easier to find. The Null signal is usually 90 degrees from the signal source.

Attenuators may be very useful in this case when you get closer to the transmitter.

There used to be low cost directional loop antennas for around $20-25, not sure if these are still readily available.

Also make sure your current antenna coax and connector are in good condition and do not have a broken/bad shield or other connection/conductor.

 

[schneijt]

Thanks everyone, I appreciate all the replies. I think the key for me is going to be attenuating the signal when I'm closing in on the transmitter, and maximizing the directionality of the antenna. Clearly my issues thus far are that near the transmitter, I'm not able to determine a direction. I haven't been out to test it further, but I'll figure out what distance I can get a pretty good direction from, and then figure out how to slowly attenuate it as I get closer to the source. My electronics on my rockets beep after the flight, so I don't have to get right on top of the rocket, but just figure out the right direction to walk in and get close to the rocket if it goes out of sight and I don't see where it comes down. I'm thinking that variable attenuator phask linked to would be great, as well as making sure I already have my scanner attenuation turned on when I'm near the transmitter. Maybe an antenna upgrade someday would be worthwhile, but for now I'm guessing the current antenna and lots of practice will help me figure out the most beneficial use for my rocket finding needs.

Thanks again,
Joe

 

[W8RMH]

Don't fault the scanner for not doing something it was not designed to do.