BRB

Wondering if anyone uses a BRB radio transmitter as a back up to a BRB 70cm gps unit. If so any helpful hints in doing so. Little history on the reason I ask. When I stated flying the BRB gps unit I would use my L&L radio tracker as a back up. I got away from it for a couple reasons. I became more at home with the gps unit and having/using two receiving units was a pain.
On a recent flight I had an issue with my gps ( battery lead broke during flight) leaving me with out tracking.
Gives me second thoughts above not using radio tracking as a back up.
Wanting to avoid the need for two receivers thought I would try using a BRB transmitter, butting it on band A of my Kenwood and the gps unit on band B. It would be nice if it was that simple but I think there could be issues in doing so.
I sent Greg an email on this. I have not heard back from him yet but sure I will. He is good to deal with.
Thought I would post the question here also.
Helpful tips/experiences appreciated.

I have a Yaesu VX-8GR, which supports APRS on the B receiver. I often run 2 gps units (time shared) through the B-side and 2 BRB transmitters (with different output frequencies and squelch off) to the A side. I use the arrow attenuator so that I can offset the BRB transmitters when necessary, which does not affect the B-side gps units. Yes, it's a bit of a symphony.

Jim

Thanks for the info Jim.
Would you mind sharing the frequencies you use?
I would like to see how far apart you keep them.
In regards to the transmitter.
Instead of using an attenuator I was thinking about offsetting the freq. setting on the receiver. If need be.
Your thoughts on that.

lmt56 said:

Thanks for the info Jim.
Would you mind sharing the frequencies you use?
I would like to see how far apart you keep them.
In regards to the transmitter.
Instead of using an attenuator I was thinking about offsetting the freq. setting on the receiver. If need be.
Your thoughts on that.

Click to expand...

Looks like I use 440.1 on the A radio for the beepers (reading the attenuated on 444.1) and 434.1 for the gps units. I would recommend the attenuator and not offsetting the frequencies. My experience with the BRB beepers is that you have to read the signal strength on the meter (as opposed to listening for a difference in volume). Therefore, you need to be able to set the signal strength with precision, so that the maximum signal is at approximatelyl a medium level on the scale. I don't think it is practical to do that by offsetting the frequency. Also, using both the A and B radios requires some practice. You don't want to be hunting for an optimum signal strength, along with everything else going on, while a bird's in the air. The attenuator makes this a bit easier.

Jim

Ordered an attenuator. They are a little proud of those things.

I've flown both a couple of times. I use a Kenwood D-7 for the GPS and just let it do it's thing. I actively use a Radio Shack scanner for the Beeline Tx. It has an Arrow 7 element and an attenuator on it. I purposely pop my main higher up so that I have time to zero in on the rocket with the Tx gear. Zero in sounds good but...depending on how far out your rocket is can be a mile or two..or three. I actually like the "rocket hunting aspect of rocketry. After a few hours I'd turn to the GPS. After a day of "lookin" it time for full on hunting.

I'll draw lines in the dirt where I'm standing (with my foot) marking strong signals. I look way off in the distance to see land marks. I even close my eyes to enhance my listening. I've even had to resort to watching video and math to find a rocket that took a less then straight flight path...drove right to it. It's all fun...Even the rockets that are officially classified as "misplaced" get me to thinking at times.

Tony

Tony & Jim Thanks for the input. Once the attenuator arrives and the weather improves it will be time to do some practice. If it is to much of a pain I will just go back to using the L & L transmitter as a back up.

At last some nice weather. Got some practice in with the BRB transmitter only. Working up to using the transmitter and gps unit at the same time. For todays practice on the reception end I was using a Kenwood D72 with an Arrow 7 element yagi and an Arrow attenuator.
My take away from the test was that with the attenuator in place and turned off or turned on at the lowest setting my reception distance was reduced versus when I removed the attenuator. The difference was about .3 mile. I was not expecting that with the attenuator in place and turned off. New to using the attenuator just wandering if that is normal?

lmt56 said:

At last some nice weather. Got some practice in with the BRB transmitter only. Working up to using the transmitter and gps unit at the same time. For todays practice on the reception end I was using a Kenwood D72 with an Arrow 7 element yagi and an Arrow attenuator.
My take away from the test was that with the attenuator in place and turned off or turned on at the lowest setting my reception distance was reduced versus when I removed the attenuator. The difference was about .3 mile. I was not expecting that with the attenuator in place and turned off. New to using the attenuator just wandering if that is normal?

Click to expand...

My impression is that attenuation occurs with the unit on at the lowest setting. However, I thought that the signal just passed through with the unit off. I haven't done the testing you described to prove that though.

I had an interesting experience a few weeks back. Two of us were out searching for wayward rocket with similar radio gear. The other system didn't have an attenuator but my system does. Several times, he was able to hear a faint signal and I couldn't. I wonder if this is related? I'm going to follow up.

Jim

I believe in the full body attenuation system. Take your 7-element Arrow antenna and place it vertical next to your chest. Compare that to horizontal orientation on the same direction angle--perfect attenuator!

My experience with the arrow attenuator:

Placing it in line but off DOES attenuate the signal, quite a bit. I'm not sure why from an electrical standpoint.

Using it, I track without the attenuator until I'm starting to get full scale signal across more than 90 degrees of sweep with the antenna. At that point the attenuator goes in, retune up 4Mhz, and with it just clicked on, I get enough signal to continue tracking. Then it's a matter of dial it down to keep the signal meter in the middle of its range. Note, the knob is very sensitive.... I've had some issue with signal strength changing on me because my thumb was resting on the knob.

Nat

Wingarcher said:

My experience with the arrow attenuator:

Placing it in line but off DOES attenuate the signal, quite a bit. I'm not sure why from an electrical standpoint.

Using it, I track without the attenuator until I'm starting to get full scale signal across more than 90 degrees of sweep with the antenna. At that point the attenuator goes in, retune up 4Mhz, and with it just clicked on, I get enough signal to continue tracking. Then it's a matter of dial it down to keep the signal meter in the middle of its range. Note, the knob is very sensitive.... I've had some issue with signal strength changing on me because my thumb was resting on the knob.

Nat

Click to expand...

Interesting. I think I'll test this myself (although I think I've already kind of done that). I'll report back.

Where you need the attenuator the most (or where I do anyway) is while the rocket is still in the air, and you have only a couple of moments to nail down the "cone" where it lands. Sorry Tim - I don't know how to do that without an attenuator. If a search for a signal is necessary, then it would be easy enough to take the attenuator out of the circuit until the signal is located. Thanks for the heads-up on this.

Jim

JimJarvis50 said:

Sorry Tim - I don't know how to do that without an attenuator.

Click to expand...

It is the Troj method: https://www.rocketryforum.com/showthread.php?16703-Looking-for-RF-Attenuator&p=146338#post146338

Wingarcher said:

My experience with the arrow attenuator:

Placing it in line but off DOES attenuate the signal, quite a bit. I'm not sure why from an electrical standpoint.

Using it, I track without the attenuator until I'm starting to get full scale signal across more than 90 degrees of sweep with the antenna. At that point the attenuator goes in, retune up 4Mhz, and with it just clicked on, I get enough signal to continue tracking. Then it's a matter of dial it down to keep the signal meter in the middle of its range. Note, the knob is very sensitive.... I've had some issue with signal strength changing on me because my thumb was resting on the knob.

Nat

Click to expand...

I agree. Looks like leaving the attenuator off until needed is the way to go. .3 a mile can be huge. I know when tracking from a road stopping at a high point and or getting up on the tailgate of my truck can be a big help.

I have not tracked seriously while rockets are in the air... we're on the east coast and our waiver is 10k. Our club takes launch trajectories very seriously and our splash zone control is quite good so we know basically where to go start looking. Lets put it this way, I know it's not behind the flight line, nor terribly far off. The one check I do while it's in the air is watch the signal meter. It's usually off scale or very strong and then drops to 1 or 2 bars on landing. If it stays off scale for way too long (dual deployment gone early) I know it'll be further out. Longest recovery so far is 3 miles, but again, we knew the direction to start in, strong wind, it HAD to be down the wind direction bearing, and it was.

Nat

I finally got around to testing the BRB with/without the attenuator. There was a huge difference. I didn't try to quantify this, but with the high-power BRB unit, the difference would equate to miles. I also noticed that when the switch was turned on, the signal (at the base frequency) improved. No idea why.

Just for fun, I might try to build a bypass so that the signal goes to the attenuator but also straight into the radio. It probably won't work, but I don't know why it shouldn't. It would be nice to have a single configuration and not have to change out the cables.

Thanks to those of you that raised this issue.

Jim

JimJarvis50 said:

I finally got around to testing the BRB with/without the attenuator. There was a huge difference. I didn't try to quantify this, but with the high-power BRB unit, the difference would equate to miles. I also noticed that when the switch was turned on, the signal (at the base frequency) improved. No idea why.

Just for fun, I might try to build a bypass so that the signal goes to the attenuator but also straight into the radio. It probably won't work, but I don't know why it shouldn't. It would be nice to have a single configuration and not have to change out the cables.

Thanks to those of you that raised this issue.

Jim

Click to expand...

I first noticed this a few years ago when testing for a large project. At 20km, the difference between having the attenuator in the circuit, and out of it, was equivalent to about 5km in range IIRC.

I was just reading the instructions for my Arrow attenuator.
Per instructions.
" Tune your receiver 4 MHz above the sought frequency."
When I did my ground testing I did not do this.
Just wandering the reason/need to do this and if it could be a common mistake we are making that is causing the reduced range problem.
The attenuator is a 4 MHz offset maybe that should tell me something.
Looks like time to do some more ground testing and follow the instructions for the attenuator this time.
Thoughts/experiences anyone.

lmt56 said:

I was just reading the instructions for my Arrow attenuator.
Per instructions.
" Tune your receiver 4 MHz above the sought frequency."
When I did my ground testing I did not do this.
Just wandering the reason/need to do this and if it could be a common mistake we are making that is causing the reduced range problem.
The attenuator is a 4 MHz offset maybe that should tell me something.
Looks like time to do some more ground testing and follow the instructions for the attenuator this time.
Thoughts/experiences anyone.

Click to expand...

The purpose for the offset is that the only source of the offset signal is from the antenna (through the attenuator). A strong non-offset signal (if that term makes any sense) can leak into the radio without going through the antenna. This is one reason why directional tracking becomes difficult when the signal is very strong (i.e., the Yagi is no longer helping you as intended).

So yes, you need to tune up 4 MHz, and then the attenuator will do what it's designed for. You'll quickly observe that even when the attenuator is turned on, that you can still monitor the signal on the base frequency (i.e., both the offset and non-offset signals come out of the attenuator). This is how I'm able to monitor an offset signal for the BRB RF tracker (on the "A" radio) while also monitoring the gps signal on the non-offset frequency (on the "B" radio). Clear as mud?

The problem I've experience is that the I assumed that the non-offset signal was just being passed through the attenuator. It turns out that the non-offset signal is attenuated as well, which affects the range when you're monitoring the non-offset signal with the attenuator in line. I presume this also affects the range of the gps signal that I'm monitoring on the "B" radio. I haven't tested this, but there is no reason to expect otherwise.

Since I often monitor two BRB trackers and two gps units on the same radio, the idea of swapping out cables depending on the status of a flight isn't very appealing. I am going to try just inserting a bypass around the attenuator (with a couple of "Y" adaptors). With any luck, this won't affect the offset signal when the attenuator is on, but will provide a direct, unattenuated signal around the attenuator without having to physically remove it from the circuit. We'll see......

Jim

Nice weather today so I did some more practice ground tracking using the BRB tx.
Some take aways.
Close range.
With the attenuator inline and the receiver tuned up 4MHz.
The attenuator needs to be turned on to receive.
Longer range with no attenuator inline.
Reception range was better when the elements of the yagi were in the vertical versus when horizontal.
Thoughts?

Which way did you have your BRB transmitter oriented? ...I'm guessing the antenna was vertical...

A simple monopole antenna (like what's on your BRB Tx) produces a polarized EM wave. The wave is polarized parallel to the orientation of the antenna. So, if the antenna is vertical, the wave is also vertically polarized. Place the BRB on its side, and the wave is horizontally polarized.

The Yagi antenna is polarized in the orientation of its elements. Place the antenna so the elements are vertical, and it is vertically polarized; horizontal, and it is horizontally polarized.

Antennas are more sensitive, by a significant factor of dB, when their polarization matches that of the signal. Odds are this is what you observed.


Practical Use

Best Reception
If the objective is maximum signal reception, and thus most reliable data transmission of GPS information, I will position the Yagi in a fashion that matches the expected orientation of the BRB, which I place in my nose cone.

• Flight: Yagi vertical
• Drougefall: my rockets are adjusted so the upper section falls horizontally, so the Yagi is horizontal
• Parachute: Yagi vertical
• Landed: Yagi horizontal

Best Direction Finding
A typical 7-element Yagi exhibits better beam performance parallel to the elements. That is to say, a horizontal Yagi will be more directional left-to-right, than it will be up-and-down.

So, when attempting to RDF a bearing toward a transmitter, I will hold the Yagi in the horizontally polarized position, even if the transmitter is vertically polarized. I will accept worse range in favor of a sharper peak on the S-meter.


Hope this helps.

All the best, James

BTW, what I haven't seen really articulated here is the reason for using an frequency-shift (offset) attenuator.

As you recall from your Ham Radio test, in order for a receiver to listen for a particular frequency, it has to generate that frequency first. This is internal to the radio and used in the tuner section.

Although every effort is made to shield this signal, and keep it inside the radio, some still leaks out. If you are attempting to RDF a very faint signal, this can make your life miserable, as the signal from your own radio interferes.

The offset attenuator allows you to tune your radio 4 MHz away from the RDF signal, thus, any leakage becomes a non-issue and allows tracking the signal cleanly.


All the best, James

Fdog said:

Which way did you have your BRB transmitter oriented? ...I'm guessing the antenna was vertical...

A simple monopole antenna (like what's on your BRB Tx) produces a polarized EM wave. The wave is polarized parallel to the orientation of the antenna. So, if the antenna is vertical, the wave is also vertically polarized. Place the BRB on its side, and the wave is horizontally polarized.

The Yagi antenna is polarized in the orientation of its elements. Place the antenna so the elements are vertical, and it is vertically polarized; horizontal, and it is horizontally polarized.

Antennas are more sensitive, by a significant factor of dB, when their polarization matches that of the signal. Odds are this is what you observed.


Practical Use

Best Reception
If the objective is maximum signal reception, and thus most reliable data transmission of GPS information, I will position the Yagi in a fashion that matches the expected orientation of the BRB, which I place in my nose cone.

• Flight: Yagi vertical
• Drougefall: my rockets are adjusted so the upper section falls horizontally, so the Yagi is horizontal
• Parachute: Yagi vertical
• Landed: Yagi horizontal

Best Direction Finding
A typical 7-element Yagi exhibits better beam performance parallel to the elements. That is to say, a horizontal Yagi will be more directional left-to-right, than it will be up-and-down.

So, when attempting to RDF a bearing toward a transmitter, I will hold the Yagi in the horizontally polarized position, even if the transmitter is vertically polarized. I will accept worse range in favor of a sharper peak on the S-meter.


Hope this helps.

All the best, James

Click to expand...

Hey James
Thanks for the input.
For the ground test I did today the antenna for the BRB tx was in the horizontal .
Results did take me by surprise.

Meh. Go figure! I'd have to say those results would take me by surprise, too.




All the best, James

It helps to understand how the receiver works. (Well most since we now have some that operate without an IF section.)

The IF is created by using a mixer combining the signal from the antenna and an oscillator. This produces the same signal out on each or four frequencies: the original signal, the added oscillator, the sum of these and the difference. You then change frequencies by changing the oscillator frequency. The gain of the radio is directly affected by the magnitude of the oscillator feeding the mixer.

Your offset attenuator is using this same technique choosing an input oscillator with a 4 MHz frequency. You then tune your radio 4 MHz off the desired frequency and are able to attenuate the signal by varying the input level of the oscillator. This also gives you a nice smooth adjustment of the attenuation (or turning down the gain). As noted earlier, in some cases it helps against leaks into the radio. In modern radios, it also happens to help against overload where nearby signals can't be filtered out.

Another alternative is to build a switched antenuator typically allowing you to increase attenuation by flipping switches on stages that have 10 or 20 db each with one stage set to 5 db.

Another option for work fairly close is to look up TDOA. This switches between two antennas causing an audio signal to be superimposed on the radio if one antenna is closer than the other. It leaves a 180 degree ambiguation unless you introduce phase sensing. But for our work, I doubt it is a big deal given you know what direction the rocket (target) went. These allow you to walk right up to a target with no adjustment. You simply swing back and forth walking in the direction that has no extra tone on it.


Sent from my iPad using Rocketry Forum

Just curious if at a launch and you have say 5 to 10 different people using the BRB is it a good idea to have them all on the same freq as you would in a normal APRS network. You could then have one base station with an antenna up say 10 mtrs. This would have good ears and be able to digipeat any signals it hears.

73

Chris

V2rocketeer said:

Just curious if at a launch and you have say 5 to 10 different people using the BRB is it a good idea to have them all on the same freq as you would in a normal APRS network. You could then have one base station with an antenna up say 10 mtrs. This would have good ears and be able to digipeat any signals it hears.

73

Chris

Click to expand...

The BRB is programmable to 1/20 of a MHz so it is unlikely you'd have a conflict especially if you have a frequency board posted at the launch.

V2rocketeer said:

Just curious if at a launch and you have say 5 to 10 different people using the BRB is it a good idea to have them all on the same freq as you would in a normal APRS network. You could then have one base station with an antenna up say 10 mtrs. This would have good ears and be able to digipeat any signals it hears.

73

Chris

Click to expand...

I'm absolutely with you, this makes sense to me - use a high gain base station antenna...preserve bandwidth...win-win.

Unfortunately:

• The concept is pretty foreign
• There's not enough APRS users at big launches to make use of the capabilities.

All the best, James

dixontj93060 said:

The BRB is programmable to 1/20 of a MHz so it is unlikely you'd have a conflict especially if you have a frequency board posted at the launch.

Click to expand...

In the schema proposed by V2, there would be no frequency conflict. This is how APRS is actually done in the Amateur Radio world - a common frequency. Heck, we use a common frequency for off-roading APRS reporting to keep track of other vehicles, so why wouldn't we use it for rockets?


All the best, James

PS: KN for V2rocketeer, 73's back at you, KF7WXY

I often use 2 of the BRB gps units on a flight. I worked with Greg at BRB to set up the timing so that they wouldn't interfere with each other (they transmit at 10-second intervals with a 5-second offset). My impression at the time was that we needed to do that because if the transmissions overlaped, they would interfere. That would be my concern with operating multiple units on one frequency (unless someone can verify that this doesn't happen).

Jim