Wullie, Since your isolator was manufactured to operate on a frequency that is close to your desired 2m frequency, there is the possibility that you can field-tune it without having it reworked. If the body of the isolator gets hot during operation, after field tuning, it means that it probably should be re-manufactured due to excessive internal losses. Go here for the Sinclair tuning procedures: <www.repeater-builder.com/sinclair/isolator-tuning-instructions.pdf> It is very important that the two dummy loads be as close to 50 ohms as possible. Note that the larger of the two dummy loads should be in the position closest to the antenna or duplexer, since it absorbs the majority of reflected power. Isolators that have been in service for some time, especially those that have endured years of heating due to excessive reflected power, often will have dummy loads that have drifted away from 50 ohms. You can't properly tune an isolator, even when using a vector network analyzer, if the dummy loads are not very close to 50 ohms.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Wullie Sent: Saturday, June 13, 2009 2:11 AM To: [email protected] Subject: [Repeater-Builder] Re: Sinclair Dual Circulator Help Hi all. Many thanks for the replies so far. The original Circulator was tuned for 142 MHz so hopefully it would tune ok to 145MHz. I have access to test equipment like Sweep generators and RF test set (IFR 2945) and the R$S Scalar Network analyzer that I used to setup the duplexer for the local UHF repeater. It would be nice to get the Circulator up and running if possible, any help is greatly appreciated. 73 for now Wullie GM0MZB --- In [email protected] <mailto:Repeater-Builder%40yahoogroups.com> , "Eric Lemmon" <wb6...@...> wrote: > > 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:Repeater-Builder%40yahoogroups.com> > [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Wullie > Sent: Friday, June 12, 2009 12:22 AM > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > 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
