900mhz yagi + frequency meter for find rocket

I wonder if I can use a frequency meter with a build in power meter and a 900mhz yagi to find a 900 transmitter like a Eggfinder by the old fashion way in case the GPS fail. Of course I will need some kind of signal attenuater

900mhz yagi


900 selectable meter


https://www.etmpacific.com.au/content/etm770-signal-strength-meters

The question is will that meter receive the FSK modulated signal that emanates from the EF for it to be any use for tracking?
Those Yagis' for 900 aren't very pricey and might help for a complicated recovery of a rocket that's already down some distance away
from the last known packet. One could use it with the EggFinder receiver and it could give one a little extra ground distance.

I used a DVB dongle to display a spectrum on a laptop but that isn't practical for field use:

https://gqrx.dk/

https://sdrsharp.com/

I had the dongles around and they're cheap enough to play with.

If you know someone who has one of those meters, it would be best to test it out first before investing in one of the devices. Kurt

You could simply put a Yagi on the Eggfinder LCD receiver and sweep the area if you lose the signal on the ground. Once you get a packet, it will tell you exactly where it is. A field strength meter isn't really much help, except in the case where you have a hard landing and the antenna from the GPS module breaks off but it's still sending out data (albeit without a GPS fix). The reality is that if you have a landing like that, you will probably be led to whatever remains of your rocket from the last transmitted fix before impact.

I've also been working on getting RSSI data from the Hope RF module, but so far it doesn't seem to be very reliable. If I can get it to work, it will be in a future software update.

Area66 said:

..... to find a 900 transmitter like a Eggfinder ..

Click to expand...

please note the work like.... what I want is a RF solution to track and find any 900mhz transmitters. I plan to use very small one that fit in a 24mm coupler, that will exclude the eggfinder and other gps solution.

Most transmitters in the 900Mhz band are frequency hopping.
I think you'll find them hard to find without a RTSA.

If you wanted the simplest 900 MHz solution you could make, you could just take a stock Hope RF HM-TRP module and have an ATTiny85 (or the PIC equivalent) feeding it a constant serial data stream (maybe your Ham call sign), with about a 10% duty cycle. Power it with a 1S LiPo, and this should fit in an 18mm motor mount tube.

Area66 said:

please note the work like.... what I want is a RF solution to track and find any 900mhz transmitters. I plan to use very small one that fit in a 24mm coupler, that will exclude the eggfinder and other gps solution.

Click to expand...

cerving said:

If you wanted the simplest 900 MHz solution you could make, you could just take a stock Hope RF HM-TRP module and have an ATTiny85 (or the PIC equivalent) feeding it a constant serial data stream (maybe your Ham call sign), with about a 10% duty cycle. Power it with a 1S LiPo, and this should fit in an 18mm motor mount tube.

Click to expand...

And I have already 4 of them ..... and what if I can make a signal meter to put it between the Eggfinder receiver and the Yagi, it will serve both purpose

[not a lot of hard data here, but...off I go, anyway] I've done bunches of amateur radio transmitter hunting in the 430MHz band and lower (lots on 2m, competitively), and I've tried a bit at 900MHz with a yagi much like the one in the photo above. I can't speak for anyone else, but direction finding at that frequency with a 5+ element yagi appears to be *very* challenging. The antenna pattern is tricky, and reflections are everywhere. These short wavelength signals bounce off of everything. I haven't given up - I've got a 900MHz BRB beacon (in addition to a couple on 70cm), and I've also listened to the FSK of the Eggfinder on an amateur receiver, but I'm not ready to DF either one with any reliability. Maybe it's my flaky 900MHz Yagi, or the operator. YMMV.

Interested to hear other experiences, and hopeful that Cris is successful with the RSSI data output from the module.

Mark

My experience with yagi's and 900MHz ISM on the ground receiving NMEA/UBX sentences has yielded a fairly effective means of establishing a general heading simply by sweeping around the yagi until you get a sentence update (which net's you current location anyway), and continuing to sweep until sentence updates stop. Generally smack down the middle of the "start/stop" sweep angles is the general heading to the rocket.

I am making RSSI available for display as part of the Telematics HMI displays I'm working on... it's effectively redundant (as you have a navigational solution with a packet update), but yet another means of validating a general heading whilst one is out rocket hunting.