Hi,<br /><br /><br />&gt; My guess is that the filters in the schematics had a different<br />&gt; unbalanced impedance than the ones they ended up placing on the c139.<br />&gt; But I&#39;m not an EE, and that is just a guess.<br /><br />Mmm, I doubt that. The filters probably had 50 ohm impedance as spec.<br />But the circuit before that / the antenna maybe was a bit off and they tuned it, or it might just be cost optimized, or they just tested and it worked better like that.<br /><br />But anyway, it&#39;s probably tuned for 50 ohm unbalanced, so you can use it as is.<br /><br /><br />&gt; My question is, does this matter? <br /><br />Truth is ... not that much. If you look at the end of the page, you can see I tried the most botched up job _ever_ and it _still_ worked pretty good !<br /><br /><br />&gt; That is, should I use the same balun<br />&gt; that Sylvain chose or should I find one with a different unbalanced<br />&gt; impedance?  Alternatively, should I use the same baluns and just install<br />&gt; an inductor (or capacitor on DCS) to ground so that it matches Sylvain&#39;s<br /><br />Just use the same, it&#39;ll work fine.<br /><br /><br />&gt; (As an aside, the baluns that Sylvain chose aren&#39;t perfect for the US<br />&gt; frequency range, but they should work okay.)<br /><br />The hi band one if the one recommended for both PCS and DCS.<br />For the low band it&#39;s indeed E-GSM but the graphs are virtually flat, insertion loss varies by less than 0.5 dB. Return losses are a bit higher but I doubt that it matters much.<br /><br />So yeah, not perfect but certainly not gonna be noticeable.<br /><br /><br />Cheers,<br /><br />    Sylvain