OK, I have to comment, An isolator/circulator should not be used in a duplexer at the antenna connector when there are other strong signals floating around the air that can get into the isolator. The strong transmit signal will mix with off air signals in the circulator BECAUSE IT IS NOT LINEAR ENOUGH!
There is an intermod combination with your frequencies! 145.25TX with 145.05TX will produce a 5th order IM at 144.65RX. Look at the spacings for multiples, 200KHz to 400KHz and 600KHz. If there wasn't an IM potential, you need 2 antennas separated by 40 to 50dB (30' vertically) and 16 7" Q (FQ20107*2) style cavities (quoting Sinclair parts due to my knowledge of them). The 145.25/144.65 on one antenna and 145.05 and 144.39 on the other. Each antenna would start off as a Q202 Sinclair duplexer and 2 more Q cavities added to each equipment leg to reject the other antenna's nearest frequency, namely, 145.25TX leg needs 2 Q cans rejecting 145.05, 144.65RX leg rejecting 144.39 only (cause 145.05 is rejected enough with the Q202 response to 145.25 frequency and antenna separation), 145.05 TX/RX leg needs 2 Q cans rejecting 145.25 (same arguement for 144.65 as above) and 144.39TX/RX rejecting 144.65 with 2 Q cans. All Q cans set to 0.6dB insertion loss by themselves and rejections for 200, 260, 600 and 690KHz are 24, 27, 38 and 39dB respectively. Approximate insertion loss is 3.2dB per leg. Can't help you with the size problem....physics unless you want to use Reslok style and have about 80% higher insertion loss. BTW, Circulators have non-linear parts in them as well as nickel plating and ferromagnetic material. Harold, VA3HF --- In Repeater-Builder@yahoogroups.com, "John Barrett" <[EMAIL PROTECTED]> wrote: > > I'm basing those isolation figures on a calculator I found online that asked > for the gain of the antennas and the separation (horizontal or vertical) > > > > Re splitting the simplex: a circulator with the radio hooked to the input, > the transmit chain on the standard output, and the receive chain feeding the > load port is what I was thinking - a relay would do the job just as well, > but would require changes to the PC based Packet Engine software to support > flipping the relay before and after transmitting. I don't think that's a > built in feature, and source code is not available. > > > > Re 4/5 ports: I have 3 transmit frequencies. 144.39, 145.05, and 145.25, and > 3 receive frequencies. 144.39, 144.65, and 145.05 - if I keep transmit and > receive on separate chains, I only need a 4 port splitter/combiner on each > chain. if I go full out with all BP cavities, combined transmit/receive > chain for the simplex rigs, and no circulators/isolators, I need a 5 port. > If I understand the products correctly, a standard star coupler is just > resistance on each port to balance the impedance presented, and there is no > port to port isolation. I feel I would be better off with a Wilkinson at > that point because it would give me some additional port to port isolation, > and If I'm reading it right, for about the same insertion loss. > > > > I have approximately 18"x18"x60" without moving cans to the cargo bay. > perhaps a little less - I'll have to measure - say enough for 9 5-6" cans, > or as many as 18 of the smaller cans that I have - the cans I have are a mix > from 5" to 8", with the idea that the larger cans would be used where I > needed sharper skirts, on the close spaced frequencies. The key here is the > height of the cans. if they are short enough (less than 30" total including > tuning rod), I can do 2 banks, facing different sides of the trailer.. > doubling the number of cans I can pack in. Only one of the cans I have so > far exceeds that spec, and only by a little.. once its tuned it may be less > than the 30" max, or I can trade it off with a shorter can on the other side > to make up the difference. > > > > I would prefer to keep all the cans on one side if possible, but it is > looking more and more like it will not be, so I'm willing to give up some > space in the power electronics bay to make space for more cans. > > > > _____ > > From: Repeater-Builder@yahoogroups.com > [mailto:[EMAIL PROTECTED] On Behalf Of Jeff DePolo > Sent: Tuesday, October 23, 2007 6:43 PM > To: Repeater-Builder@yahoogroups.com > Subject: RE: RE: RE: [Repeater-Builder] Re: duplexer isolation and reciever > noise budget > > > > > If I do two antennas, the best I can do is about 30db > > isolation (30ft separation, 6db multi-bay folded dipole > > antenna on bottom, 9db 2m/440 base station antenna on top), > > If you can get 30 feet of separation, you'll get more than 30 dB of > isolation. More like 50 dB on VHF, 60 dB or more on UHF as a guess. > > > Going to split the simplex radios with a circulator on each.. > > Maybe I'm missing something. I was talking about splitting the transmitter > and receiver apart so you could combine the transmitters separate from the > receivers if you were going to use hybrids as the primary means of > combining. > > > I've done some checking around for "stars".. haven't found > > any - I'm combining three transmitters - so 4 ports ?? > > You have four frequencies (144.39, 144.65, 145.05, 145.25), plus an antenna. > Five ports. > > > got > > some vendors or links I can look at > > Try Delta Electronics, Pasternak, maybe Kings. A 4-port "cross" is easy to > find. It's easy to build stars with more ports in a small die-cast box (the > > ideal-sized box would make all of the center pins of the connectors > coincident). > > > If I can use the star > > to eliminate hybrid couplers, that would be great :-) that > > would leave me with a 2 stage isolator and one or more cans > > per transmitter. > > Split antennas is, by far, the best way to go. Your biggest problem is the > 145.05 Tx/Rx versus 145.250 Tx. I'd be inclined to start doing the analysis > assuming 145.05 is on its own antenna, with the remaining frequencies > three-wayed on another antenna using conventional cavity-ferrite combining. > > > I don't have t-pass cavities, but since I'm still acquiring > > cavities, I can get them if warranted. I've got 4 regular > > band pass cans right now, 2 more on ebay I'm trying to get, > > and a 6 can helical BR/BR duplexer that I can use for a > > really deep notch if I need it somewhere (or will become part > > of the receiver filters if I decide to stack BR filters for > > receive, as per my previous post) > > A helical pass/reject duplexer isn't going to help with the close spacings > involved. You might get lucky and be able to it to get some filtering > between the extremes (144.39 vs 145.25), but otherwise, the notches aren't > going to be sharp enough to avoid degrading the frequencies in between. > Have you swept it to really see what its performance is like (both > transmission and reflection)? > > How much room do you have? > > --- Jeff >
