What about factory-installed circulators, such as those in a UHF Motorola MICOR station/repeater? Who can those be sent to for proper retuning?
-----Original Message----- >From: Eric Lemmon <[email protected]> >Sent: Jun 12, 2009 8:48 AM >To: [email protected] >Subject: RE: [Repeater-Builder] Sinclair Dual Circulator Help > >Wullie, > >If the isolator was made for a frequency that is more than 4 MHz away from >your 2m transmit frequency, it cannot be tuned to work properly that far >away from its design frequency. No matter who makes the unit, each isolator >(which is called a circulator if dummy loads are not provided) is >made-to-order for a specific frequency. The catalog descriptions of such >devices are very misleading, since the description often says something >like, "136-174 MHz," which means only that the company can manufacture an >isolator to work within that range; it does NOT mean that an isolator can be >field-tuned to any frequency within that range. A very informative article >on this topic is found here: ><www.repeater-builder.com/antenna/ant-sys-index.html#iso-cir> > >Several years ago, I acquired more than a half-dozen Sinclair dual isolators >that were part of a military VHF radio system. Some of these isolators were >made to work around 138 MHz, while others were made to work around 163 MHz. >I quickly discovered that none of them would perform properly at 2m. I >contacted Sinclair and learned that I could have any one of them >re-manufactured to a specific 2m frequency for $250- about 1/3 the cost of a >new unit. The only prerequisites were that the two dummy loads be in good >condition, the isolator works properly at the frequency stamped on the unit, >and that the case had never been opened since it left the factory. The >radio club shipped the used isolator to Sinclair along with a check, and we >received a perfect isolator, with a guarantee, in about two weeks. It is >still in service. > >Every time this topic comes up, a few posters claim that they have re-tuned >a commercial-frequency isolator to 2m, and further claim that it works >perfectly. Baloney! Proper tuning of a circulator or isolator takes a >network analyzer, or at least a good spectrum analyzer with tracking >generator and a return-loss bridge. There's no way that an isolator can be >tuned properly by simply adjusting the caps for maximum forward power. It >takes some precision grinding, machining, and lapping to very close >tolerances to manufacture a circulator, or to modify it for a new frequency. >The magnetic properties of the pole pieces must be carefully adjusted to >match those of the ferrites. This is a very exacting process, and it >results in a unit that will work properly only over a narrow band of >frequencies- usually less than +/- 2%. Nevertheless, there are misinformed >people "out there" who will lead you astray. If you want your repeater to >function properly, please have your isolator properly tuned to your >frequency. An incorrectly-tuned isolator may SEEM to be working properly, >but can be very unstable when the load impedance shifts, and can cause >severe damage to the PA or to itself. > >73, Eric Lemmon WB6FLY > > > > >-----Original Message----- >From: [email protected] >[mailto:[email protected]] On Behalf Of Wullie >Sent: Friday, June 12, 2009 12:22 AM >To: [email protected] >Subject: [Repeater-Builder] Sinclair Dual Circulator Help > > > >Hi All > >I recently purchased a Sinclir I2210A Dual Isolator for our local 2m >repeater. I was wondering if there is anyone out there who has information >on how to align this device ? > >Kindest regards > >Wullie GM0MZB > >Keeper GB3FE and GB3OH >
