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: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Joe Sent: Friday, February 05, 2010 6:55 PM To: Repeater-Builder@yahoogroups.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>
