On 2/5/07, Barry C' <[EMAIL PROTECTED]> wrote: > Upping the power changes the balance , if you really need to fiddle with it > improve the antenna for a boost both ways and at no additional running cost
Unless you're running separate antennas, how would changing the gain of the antenna make a difference in additional gain for RX that wouldn't be also seen in additional gain for TX? But unless I'm missing something here (deep nulls and fading due to terrain or something?) the added gain of a better antenna on receive would translate to the same on TX, doesn't it? The only reasonable way to get more RX without affecting TX would be (pre-)amplification of the receive chain and additional filtering if necessary to avoid desense, etc. If there's a suspicion that the system isn't performing as absolutely well as it can on RX, a usable receiver sensitivity test with a weak signal injected into the RX chain with the antenna connected also, would be the way to find out. Jeff's article about measuring the sensitivity of a receiver WITHOUT the site noise/antenna connected is here: http://www.repeater-builder.com/tech-info/receiversensitivity.html And doing it WITH the site noise/antenna is here: http://www.repeater-builder.com/tech-info/effectivesens.html If there's 2 or 3 more dB "available" between the site noise floor and the receiver's best sensitivity measurements -- then sure, maybe you can squeak all of that out with better filters, a good LNA and balance the added TX power. That will take additional money/time/effort beyond just swapping the PA for a bigger one and checking for desense. And... no one's posted this here in the discussion yet... http://www.repeater-builder.com/antenna/3db.html ... which of course, is a good discussion of the situation too, since it actually starts with the same theoretical question (should I add 3dB to my transmitter?) and tackles the analysis of adding 3dB to a system mathematically. Hopefully the above articles help. And if you haven't done the Effective Sensitivity test, do it BEFORE you make any changes. It will give you a baseline so you know if relatively you're making things better, or worse, overall on RX. Nate WY0X
