Fiberglass threaded rod to avoid RF attenuation

[iter]

Yes, I'll be at Dairy Aire. I'll be doing some s4 stuff with a couple of High Schools.

I'll be sure to bring some Nomex.

Tony

Hey, you know, if you need some, this really good friend of mine gave me a pair of old Nomex fireman pants a while ago...


Ari.

 

[iter]

OK, so how about wires that go to deployment charges? These often run parallel to the antenna. Do these affect RF?

Ari.

 

[Walldiver7]

OK, so how about wires that go to deployment charges? These often run parallel to the antenna. Do these affect RF?

Ari.

YES! Big time! My tracking experiences began with a TeleMetrum housed in the Av-bay. It worked fine with the shock cord running through the Av-bay (no metal all-thread) and ONE (twisted!) igniter wire running from the Telemetrum to the aft bulkhead (these were apogee-only deployment rockets) to pop the single bp charge (motor ejection was also used as a backup). Later when I flew with the Telemetrum and another computer in the Av-bay, firing typical dual deployment redundant charges (4 of them), then the Telemetrum starting losing gps lock. The actual Rf signal was also way down in strength. My problems were because I had one, or more, leads in close proximity to the TeleMetrum that were of near resonance to the frequency the Telemetrum was operating at. The additional leads also acted as somewhat of a "shield" to GPS reception. Thus, tracking became very intermittent, to none, while in flight. The solution was to solve an environmental problem within the Av-bay by getting rid of resonant length metal.
Today, I fly with a TeleGps in the nosecone attached to a nylon all-thread, and it works GREAT! I have flown to over 18K with perfect tracking.... exceptions to that being during the high G portions of the flight where GPS lock is momentarily lost.

 

[ksaves2]

Uhhh, I think it's pretty clear that parallel metal rods next to a transmitting antenna is not a smart situation. I've had a GPS receiver on a sled with the Rf transmitting antenna into the upper main chute bay that did parallel an eyebolt without any issues.
I've also had small 2-56 metal screws holding the filament nosecone on the coupler that contained an Rf tracker without range problems.

I really, really like the new filament wound nosecones that are available now. Pricey but they lend themselves to carrying a radio tracker with very little trouble. Cut a press fit sled for the tracker. Drill and tap three or four screw holes to hold the nosecone
to the coupler and epoxy a bulkhead to the base of the coupler.

I use 2-56 buttonhead screws for small nosecones and 4-40 buttonheads for larger ones. If the nosecone material is thick enough, can countersink the screw head and use a flathead screw. I find the fiberglass couplers will hold threads very nicely and I am NOT going to be using those "plastic" rivets anymore for fiberglass ebays. I'm just going to drill and tap for an appropriate screw. The plastic rivets still have a place with the cardboard tubes. Kurt

 

[iter]

My problems were because I had one, or more, leads in close proximity to the TeleMetrum that were of near resonance to the frequency the Telemetrum was operating at. The additional leads also acted as somewhat of a "shield" to GPS reception. Thus, tracking became very intermittent, to none, while in flight. The solution was to solve an environmental problem within the Av-bay by getting rid of resonant length metal.

So igniter wires are mostly a problem if they are close to resonant length? What effect does twisting them have? Would it help to use shielded, coax-style cable and ground the shielding?

Ari.

 

[Walldiver7]

So igniter wires are mostly a problem if they are close to resonant length? What effect does twisting them have? Would it help to use shielded, coax-style cable and ground the shielding?

Ari.

Any metal that is close to the resonant freq. length (that is in close proximity) is a problem. Twisting the leads coming from each computer helps reduce the possibility of RF getting back into the flight computer. I'm an old ham radio operator... they use to teach this type of stuff when you were working on your license, but today, I don't know what they're teaching.