Comant CI-507 diplexer vs RAMI AV-570 Coupler

[macrafic]

These units both seem to do the same thing; allow a Nav antenna's signal to be broken into VOR/LOC and Glideslope for feeding into NAV units such as the Garmin 430. Yet, there is a significant price difference between the two.

What is the difference? Anybody have experience with either/both? Is this a case where "you get what you pay for"?

[roee]

No experience with these particular two models, but there's a fundamental difference between a diplexer and a coupler in how they split the received signal. VOR/LOC signals are in the 108-118 MHz band, while GS signals are in the 329-335 MHz band. A diplexer ideally directs all the energy in the 108-118 MHz band to the VOR/LOC port, and all the energy in the 329-335 MHz band to the GS port. So in the ideal case, both VOR/LOC and GS receivers should receive the same signal level as if they each had their own antenna. A simple coupler on the other hand just splits the signal between the two ports without discriminating in frequency, so even in the ideal case each receiver will only receive the signal at half strength. Bottom line: a diplexer gives better performance than a coupler.

[roee]

P.S. ...and to quantify "better performance": in the ideal case a diplexer should give you about 41% longer range than a coupler.

[roee]

P.P.S. I looked up the specs on both of these, and they are actually both diplexers. The CI-507 however specifies a max insertion loss of 0.5 dB where as the AV-570 specifies a max insertion loss of 1.0 dB. That 0.5 dB difference would translate to a difference in range of about 6% in favor of the CI-507.