Wullie, Having moved many of these particular devices from 142 mhz to 145 mhz I would follow this proceedure. Check it on its original frequencies for insertion loss and isolation. The Pass band on 1db per division should be around 20 mhz.
The isolation plot will be much more narrowband ..around 1 Mhz and there should be two identifiable notches around the original operating frequencies one for each section. Tap the unit gently whilst measuring insertion loss on 1dB per division. If it is microphonic gently tap each multiturn capacitor with a plastic probeto find which one is dirty. Then take all of the pistons out of all the capacitors (5) and clean the threads with isopropl alchohol. Also clean the threads inside with a cotton bud. Return the caps to their original positions and check for microphonics again. If the circulator is still microphonic, Identify which section is faulty. Take off the sinclair label and apply a bead of superglue releasant to the round thraded plate. Make a spanner that has two 1/8" steel pegs 1/4" long at the right separation. Tighten the plate 1/4 turn clockwise and re-check microphonic performance. You may be lucky and not need to repair your circulator but most of the 142mhz ex british gas units were OK on dismantling but have been roughly treated at hamfests etc. When everything is working for you can I suggest some tape over the tuning holes to keep the dust out? Ian G8PWE ----- Original Message ----- From: "Wullie" <[email protected]> To: <[email protected]> Sent: Saturday, June 13, 2009 10:10 AM Subject: [Repeater-Builder] Re: Sinclair Dual Circulator Help > --- In [email protected], "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:[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 > > > 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 Scaler 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 appriciated. > > 73 for now > > Wullie GM0MZB > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
