Extreme xtal swapping!
10-31-2003, 01:15 PM
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Extreme xtal swapping!
The other day I did a series of tests on Xtal swapping that some will find interesting, others appalling. In short I put 72 MHz xtals in 75MHz equipment and and vice-versa in a number of combinations and found that all same-channel combinations worked with no sign of degraded performance.
First my equipment:
Transmitters--both narrow band AM, one surface, one air:
1 FP-T2NL 72MHz
1 FP-2PBKA 75MHz
Recievers--both wide band AM, one surface, one air:
1 FP-R2GS 72MHz
1 FP-R2GS 75MHz
Xtals:
1 set on CH 46 (air)
1 set on CH 86 (surface)
First setup (surface RX on air frequency):
Air TX (72MHz) with ch 46 xtal intalled. Surface RX (75MHz) with ch 46 xtal.
No glitching at 100' with antenna down.
Second setup (Air TX and RX with surface xtals installed):
Air TX with ch 86 xtal, Air RX with ch 86 xtal.
No glitching at 100' with antenna down.
Third setup (Air TX and RX with surface xtals installed, but swapped. RX xtal in TX and vice versa):
Air TX with ch 86 RX xtal, Air RX with ch 86 TX xtal.
Still no glitching.
I tried a number of other combinations and everything worked fine as long a the xtals were on the same channel. Of most interest to me is that a 75MHz RX will work fine on 72MHz. This means that I can put my old AM ground frequency RX's into slope fliers. I'm not recommending this to anyone, BTW, especially not club fliers. But for those who fly planes that are meant to be crashed (combat, foamies, etc) and/or fly alone in remote areas, this may be an inexpensive way to get a plane in the air. Please don't try this in any planes that you care about, and definitely not in populated areas. Please note that putting an Rx xtal into a Tx causes out of band transmissions and should NEVER be used.
Also, while swapping TX xtals is technically illegal, especially if you swap between bands, swapping RX xtals is OK even between bands.
First my equipment:
Transmitters--both narrow band AM, one surface, one air:
1 FP-T2NL 72MHz
1 FP-2PBKA 75MHz
Recievers--both wide band AM, one surface, one air:
1 FP-R2GS 72MHz
1 FP-R2GS 75MHz
Xtals:
1 set on CH 46 (air)
1 set on CH 86 (surface)
First setup (surface RX on air frequency):
Air TX (72MHz) with ch 46 xtal intalled. Surface RX (75MHz) with ch 46 xtal.
No glitching at 100' with antenna down.
Second setup (Air TX and RX with surface xtals installed):
Air TX with ch 86 xtal, Air RX with ch 86 xtal.
No glitching at 100' with antenna down.
Third setup (Air TX and RX with surface xtals installed, but swapped. RX xtal in TX and vice versa):
Air TX with ch 86 RX xtal, Air RX with ch 86 TX xtal.
Still no glitching.
I tried a number of other combinations and everything worked fine as long a the xtals were on the same channel. Of most interest to me is that a 75MHz RX will work fine on 72MHz. This means that I can put my old AM ground frequency RX's into slope fliers. I'm not recommending this to anyone, BTW, especially not club fliers. But for those who fly planes that are meant to be crashed (combat, foamies, etc) and/or fly alone in remote areas, this may be an inexpensive way to get a plane in the air. Please don't try this in any planes that you care about, and definitely not in populated areas. Please note that putting an Rx xtal into a Tx causes out of band transmissions and should NEVER be used.
Also, while swapping TX xtals is technically illegal, especially if you swap between bands, swapping RX xtals is OK even between bands.
10-31-2003, 03:19 PM
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RE: Extreme xtal swapping!
interesting! i didn't think you would have that good of success... (and thanks for noting the illegal part, i was already getting ready to add it until i read it... and don't assume no one really cares, if you are interfering with another frequency outside of the RC band because of this, someone WILL track you down, and FCC fines are not nice...)
If would be really interesting if someone had a spectrum analyzer to actually see what they are putting out, if the bandwidth has been changed at all by crossing bands.
If would be really interesting if someone had a spectrum analyzer to actually see what they are putting out, if the bandwidth has been changed at all by crossing bands.
