Point taken. One factor that will directly affect how the subject duplexer will perform at 70cm is where the original factory tuning was. For example, if the factory tuning was in the 450-455 MHz band, such a duplexer will likely perform better at 70cm than will a duplexer that originally was factory-tuned for the 460-465 MHz band. The results I quoted were for a duplexer in the latter class.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Joe Sent: Saturday, February 06, 2010 2:59 PM To: [email protected] Subject: Re: [Repeater-Builder] RFS TDE-7780A Correct, but if I remember you were claiming 3dB loss at the pass frequencies. I was seeing about 1.5dB loss. I claimed respectable results, not perfect results. I think it is still acceptable for ham use. Everything is a compromise when you push the equipment past its limits, but the typical ham is frugal (aka me) and accepts a little degradation for economy. 73, Joe, K1ike Another parsimonious Yankee ham. 73, Joe, K1ike Eric Lemmon wrote: > Joe, > > Your screen shots actually prove my point. Both of the pass plots reveal > that your duplexer's pass response is far from optimum, which is precisely > the reason for selecting the proper duplexer model to tune. If your > duplexer was originally designed for operation in the 440-450 MHz band, the > peak of the pass plots and the nadir of the notch plots would be exactly 5 > MHz apart. Your TX pass plot shows that the peak is about 900 kHz to the > left of your desired frequency, and your RX pass plot shows that the peak is > off-scale to the right- considerably more than a MHz away from the desired > frequency. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Joe > Sent: Friday, February 05, 2010 6:55 PM > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > Subject: Re: [Repeater-Builder] RFS TDE-7780A > > > > Eric, > > I tuned up a 633-6A from a GR-300 recently and got some respectable > results. Pass frequency loss was around -1.5dB and notch loss was > around -85 to -90dB. I've attached the sweeps. > > 73, Joe, K1ike > > Eric Lemmon wrote: > >> Paul, >> >> The Motorola TDE7780A duplexer is simply a relabeled Celwave 633-6A-2N >> > unit, > >> and it is designed for 450-470 MHz. It is the standard duplexer furnished >> in GR300, GR1225, RKR1225, and CDR700 repeaters. The duplexer is okay for >> non-critical use at low-density RF sites, such as at construction sites. >> The compact mobile notch design has very little bandpass action, since its >> operation is based solely upon the notch. >> >> I have tried to tune such duplexers down into the Amateur 70cm band, with >> little success. >> > > <snip> > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > >
