# Why exactly would cable lengths to a duplexer matter?

So a very experienced friend of mine is making a portable suitcase kit with Yaesu FTL-2001 (VHF), Yaesu FTL-7002 (UHF) and DX-720D duplexer* plus power supply and other miscellaneous gear. FTL-2001 and FTL-7002 are connected to inputs of DX-720D and the output is connected to the antenna socket on the suitcase.

Originally, the coaxial jumpers were installed inside of the suitcase so that they fit as neatly as possible. Later on, he decided to change one of the jumpers so that it is of same length as the other jumper because "cables going to a duplexer need to be of same length". He couldn't provide me a better explanation than this.

This set off my WARNING! SUPERSTITION alarm, since it seems to look a lot like this question. Furthermore, to me it seems a bit strange that the same length would be very critical, since the transcievers are operating on different bands. I've read some resources about cavity duplexers where jumpers of length corresponding to certain wavelength fraction are recommended, but I haven't seen anywhere this recommendation of having same length even if the frequency bands are different.

So my question is: Is there actually any real reason to have coaxial jumpers of same physical length for connection to a duplexer?

*Note: this unit is referred to as duplexer on various websites that sell it, but it only has fixed low-pass and high-pass filters from what I see, so perhaps term diplexer would be a better fit.

• I can't think of a reason. Maybe your friend has misunderstood the reason for 1/4 wave cables in cavity duplexers? – Phil Frost - W8II Feb 24 '15 at 15:16
• @Phil Frost That's the only think I can think of now. If you feel like posting that matched lengths are a superstition, please do so, so that I may accept the answer. – AndrejaKo Feb 24 '15 at 15:28