Hi Joel. In my experiance with diode ring mixers they almost always require specific impeadance terminations on all ports. The input should look at 50 ohms, the L.O the same. The I.F port is the most important to terminate properly if the desired switching or mixing products are to be produced. In many receivers designed for high dynamic range the I.F of the diode ring is terminated into the base circuit of a very strong bipolor transistor stage using feedback many times. Because of the feedback used and particular biasing this stage can be designed tolook like near 50 ohms to the I.F port of the diode ring. This is not enough many times though. This same transistor amp stage then many times drives a crytal I.F filter that can have the correct 50 ohm term if designed that way but this term will only be 50 ohms very near the passband of the filter and frequencies that depart from this 50 ohm passband away from this freq causing this hi SWR to reflect the incorect impeadance back through the output to input of the amp missmatching the diode ring. Amp.s that use heavy feedback are even worse in this respect. In cases like this the designer many times hooks a 50 ohm pad (such as 6 db) to force a decent 50 ohm load back through the amp to the mixer. This mixer termination stuff is quite important if the mixer is to work as it should.In situations where lower dynamic range is desired for battery drain, etc, this termination MUST be provided for in other ways. The same thing holds true for direct conversion or zero I.F receive schemes, the audio preamp is biased and designed for a 50 ohm term for the diode ring. Much can be learned in literature such about this topic from Solidstate Design for the Radio Amateur, Experimental Methods in Radio Design, both by coauthor Wes Hayward, W7ZOI and much can be learned from publications by Minicircuit Lab's, the builders of many high quality DBM's for industry. Check the web, much can be learned. 73's, Doug,