On Thu, 2008-01-31 at 07:27, G4ILO wrote: > > Brett Howard wrote: > > > > So I was recently reading about the IC756ProIII and noticed that it said > > its tuner was rated for 3:1? Does that really mean that you have to > > have a 3:1 or better SWR or it can't tune it? > > > Yes it's true, and it's the same for Icom and Kenwood radios too.
If a tuner is specified to match 3:1 at all phase angles, it probably does much better than that at some phase angles. For example, the Drake MN2700 tuner is specified at 5:1. While it barely meets that spec for low impedances (around 10 ohms resistive) it does much better than that for high impedances. That is, it matches much more than 500 ohms on most bands. Very useful for matching end-fed wires. > Also you > can't assume the losses in the tuner itself are as low with a big mismatch > as they are with a good match. That's very true. The L-network used in the Elecraft tuners has the advantage of wide tuning range but, as with most most tuners, the loss depends on the antenna impedance - generally it gets worse the higher the SWR. That's why you won't see an insertion loss specification for most tuners. The PI-L network in the Drake tuners has the advantage that the insertion loss is independent of the antenna impedance (specified at 0.5 dB max in the MN2700). It also gives reasonably good filtering of out-of band signals (on both transmit and receive) which is not generally true with an L-network. Al N1AL (designer of the MN-2700 in a previous life) _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
