I think KG6ABF was hijacking the thread a little bit. What I was originally asking was, what is a lower cost method to tune a notch filter (like the mobile duplexers for home use) without a service monitor
-J
Pardon me but I was not trying to "hijack the thread", I was simply asking about tuning a duplexer that came in the desk top package of a Motorola Radius repeater. The total bandwith of the device I was using covers 144-174. If it had been a 70c (440) machine I wouldn't have needed to retune it since the standard offset in that part of the spectrum is 5 mHz.
2 meters
usually has an offset of 600kHz (some use a wider offset but most use 600 kHz as standard for 2 meters) and since the duplexer was tuned for a wider offset
(about 1.5 mHz judging for the channels in the software readout), I was just asking if it could be reduced to work in the more standard fashion. It would be in keeping with the thread since I wanted to do it without having to use a service monitor.
So, please, if you would let us all know why you chose to make a point of my post when it was directly related and more detailed in description in using a device intended and designed to cover the portion of the spectrum I asked about; as I simply wanted to know if it could or had been done by anyone here. I am asking as it exists currently without needing to add additional outside cavity filters or other devices due to space restrictions.
The package was intended by the manufacturer to cover the spectrum of 144-174 mHz and researching it I wanted to know if it would tune to a tighter offset. Some info says it can while other recommend using a separate set of tunable notch cavities. I was simply asking if anyone had done it or knew of a way without a service monitor to do so. It was directly in keeping with the original questions posed in the thread preceding my post.
KG6ABF, if the duplexer was designed for 2M or for 70cm, you are not going to get it to tune for the other band. Additionally, if it was designed for a larger split, the Q of the filter will not allow you to tune for a 600Khz split...its just not allowed in the laws of physics...
-J
I wasn't asking nor did I say I wanted to use a duplexer for something that was not intended or designed to work in the frequency range I was going to employ it for. I wanted to use it for 2 meters and it covers 2 meters. In fact some of these very same units were in use as repeaters which is why I picked it up in the first place. I am aware of several repeaters in the past listing this equipment. Some of the owners who had the additional space employed some outside tunable notch filters as well. I don't have the space for those nor do I want the added trouble of locating and buying them if I don't have to.
I intended this repeater for limited use as an emergency unit or for an event such as a weekend gathering/festival type event. A low power (less than 25 watts) to cover the necessary area for the duration of the limited event. It was not intended for permanent fixed use but more so a portable repeater. I had access to a portable unit years ago similar to this installed in a trailer and that was retired many years ago and so the need to find a replacement. That unit was manufacture by Motorola but I didn't set it up only use it once it was dropped off. I don't have a lot of experience in setting up repeater which was why I asked.
This desktop unit consisting of transmitter, receiver and duplexer covered the portion of the spectrum in which the allocation of 2 meter is found, it should be possible to tune it to a tighter or smaller offset. I simply stated what the frequencies and offset were at when I acquired the unit, that being tuned at a larger offset. I did not have a service monitor and wanted information with regard to if it had been done by anyone and could it be done. An answer to either of those questions would have sufficed to answer my inquiry.
Hope that will clear up for archjeb any confusion as to what I was asking about in my post.
Also wanted to says thanks to Browningman for his thoughtful response. One point again, the frequency coverage of the unit is designed to and covers what the operating tunable bandwith needs to be and in this case between144 to 148 mHz.
Since this unit I have was designed to operate between 144-174 (specs show a listing of 146-174, but manufacturer data sheets list an even wider frequency range of operation capabilities) and I want to set it up with in that operating range, it should be possible to tune the duplexer to a workable result. It is capable of putting out 45 watts, but I would run it at much less not exceeding 25 watts max, and most likely even less around 10-15 depending on the event and area of coverage.
Based upon the specs it would seem there is a way to use this desktop unit retuned and at reduced power to function as a temporary repeater.
The desk top repeater was designed to cover the freq range and internal duplexer specs from Motorola says it can be adjusted and/or tuned to desired splits, then it should be possible to do it, at least it seems so.
Hope that clears up any possible concerns by readers here of my intent and questions concerning the unit I asked about.
