Batboard

Question for the group with those familiar with MSF 5000 repeaters, specifically the UHF ones with internal filtering:

The "Duplexer Tee", the little silver block about 1 inch square that connects between the receiver and transmitter filter output and gives you your antenna connection is available in several different flavors.

Mine is the one with the green band around one of the connections. It's the 435-475 "Transmit Low, Receive High, 5-20MHz" one.

I recently retuned the station for a different pair, transmit high, receive low. The manual says I need the TLE5772B "Transmit High, Receive Low 5-20MHz" with the yellow band around one of the connections.

How critical is this? Do I actually need it? I've got no clue how this thing works and I'm not familiar with this screwy MSF 5000 non-duplexer type way of duplexing. Am I going to damage anything by using the existing green banded "duplexer tee", or will I suffer any degradation of signal, or what's the story?

I called Motorola Parts ID & Purchasing (800) 422-4210, and was told the TLE5772B is no longer available period. Whatsoever. Stop-bothering-us-cuz-you-aint-gonna-get-it-cuz-we-dont-got-it.

Does anyone happen to have the one I need that would be interested in trading with me, or just selling it to me?

Any help is appreciated. Please reply via PM or the thread. Thanks!

i think i have one of these that has a broken connector on one end.

i have never opened the silver box, but if you'd like mine to experiment with, lemme know and i'll dig it out.

i am certain mine is the tx low rx high style tho


doug

The MSF5000 UHF uses a PASS/PASS Cavity Duplexer setup. The Transmit Filters are the TX cavities and the Receiver Filters are the RX cavities.
The "T" connector is just that a junction of two coaxial cables. The trick here is the length of each cable, one going to the transmit filter, read Cavities, is resonate at the receive frequency. The length of cable going to the IO connector is just for convince.

You can make up a "T" by using two cables and the IO connector where the two cables are in paralell. Each cable is cut to a length so that the Receiver does not "see" the transmit filter and the TX does not see the receiver filter at each respective frequency. The TX cable acts as a high impeadence at the RX frequency and the RX cable is a high impeadence at the TX frequency as in most PASS/PASS duplexers.

So how would I configure this if I was transmitting on 446.100 and receiving on 441.100?

And what is the most ideal way to build the appropriate one I need? Any suggestions?

Nobody has a yellow banded one laying around in a dead station huh...

The new (to me) MSF5000 I'm getting supposedly has the internal duplexer but I have no idea what frequencies it was on. I'm assuming it was in the commercial band and was configured for that offset, whatever is standard.

If, however, it is for a transmit high, receive low situation, I'll gladly trade you for it, since I would need one for a transmit low, receive high setup for my repeater.

You can still toss that internal unit and go buy yourself a real duplexer, i.e. a Celwave 6-cavity bandpass/reject unit. They're on eBay once in a while for between $200 and $400. With over 100 dB of rejection, they work well with the MSF5000.

All I can do is wait until I get it however. I bought it on May 7th and am waiting for a convenient time when the seller and I can meet at a spot mid-way between our two locations. Next opportunity is this weekend; after that it's the Newington Flea Market on the 12th and 13th.

Bob M.

Bob,
Well please keep me in mind. I need the duplexer tee with the yellow band around it. Mine has the green band.

I have some UHF station duplexers laying around but would prefer to keep this MSF stock.

Please let me know. Thanks!

Will wrote:You can make up a "T" by using two cables and the IO connector where the two cables are in paralell. Each cable is cut to a length so that the Receiver does not "see" the transmit filter and the TX does not see the receiver filter at each respective frequency. The TX cable acts as a high impeadence at the RX frequency and the RX cable is a high impeadence at the TX frequency as in most PASS/PASS duplexers.

Seeing that I'll run into this problem as well. What is the formula to figure out the jumper lengths? Do I need to use a "T" box as well? Can I connect them right to a new connector in the side of the cabinet?

I do not have any low in high out T networks, BUT, the Motorola Internal "Duplexer" is so, sooooo, lossy, the first thing I do is yank them out and pitch them. The exciter filter portion isn't a bad idea, but look what they do to a 110 watt station run through them. I simply add the second antenna N-connector to the side of the cabinet and run seperate TX and RX connectors. Then you can add an external duplexer and get better results, at least in the TX loss as compared to the Moto deal.

My two bits worth:
The original version of the "duplex tee" was made up of an "N" tee with short jumpers with "N" connectors. (The receive has an SMA RT angle at the preselector.)

The later version with the box just has the wires joined in the box, cheaper than the N cables.

The cables must be 1/2 wave length, or a multiple.
Don't forget the Velocity factor for whatever cable you plan to use.
I think that the formulas would be in an ARRL handbook.

I have tuned stations for ham use, and found in my particular instance that it met spec when I was finished.
One hint be VERY sure to follow the manual exactly. Especially the terminations.
My sugestion would be to tune the station and see how it works.

As far as the "lossy" internal duplexer:
Perhaps there is a valid reason why it is so:
Perhaps the factory was overly concerned with side band noise or some other esoteric issue, and traded a few DB of transmit power for other considerations.

Years ago, I saw the prototype at base station engineering at Schaumburg. The goal at the time was to produce the next generation station with specs better than any one else.
This is very important when dozens of stations are on or near the same site.
Perhaps these conciderations are of no consequence in your application.

I do not think that a DB or two in transmit power will make very much difference in overall performance.

bernie wrote: I have tuned stations for ham use, and found in my particular instance that it met spec when I was finished.
One hint be VERY sure to follow the manual exactly. Especially the terminations.
My sugestion would be to tune the station and see how it works.

Do you mean you kept the original "T" inplace while tuning it down to the ham band? Or did you change the cables to reflect the new freq?

That's what I'd like to know as well - Bernie - Can you run "Transmit High, Receive Low" on a "Receive High, Transmit Low" tee and have it work?

Or does it cause damage?

I'm having a HELL of a time finding someone with the yellow banded tee assembly that will sell it to me or trade for my green banded one.

Stupid f***ing upside down weird ass splits (TX high RX low, though I understand the reasoning). This is the only thing keeping me from putting my station on the air.

I found someone who can order the part I need for me from Motorola, but I hardly feel the tee is worth $109.00 (NSO price), and besides, cash is too tight for me to splurge on something like that right now.

Any info is appreciated. Bernie, got a yellow banded tee laying around?

My two bits worth:
The last time I looked for the duplex tee it was un available.
Why would there be TX low, and TX high?
Often these stations were used as full duplex links, which would require the "reversed" kit.
I have tuned these up with no problem.
I doubt that you would cause damage.
The TX filters are somewhat trickey to tune.
The instructions call for a RF Milivolt meter. I have the exact instrument specified, however I have used a second analyzer in the spectrum mode instead of the muli volt meter.
If you have access to an analyzer such as the R2600 with the tracking generator option, it is possible to use the tracking genarator for alignment.

In any case it is very important that you properly terminate the filters
during alignment.
The true test is if you meet spec with out desense.
Let me know if I can help.

Bernie,
My station was aligned by terminating the filters into a dummy load, and using the factory alignment procedure (meter panel) and it was also checked using the tracking generator on an IFR 1600S.

So you're saying I could just run the station using the green banded tee that's already on it, even though the transmit high/receive low thing is upside down from the tee configuration?

Do you have any MSF 5000 parts? Happen to have a yellow banded tee?

My two bits worth:
No, I don't have very many MSF parts any more.
I gave my last duplex kit to the local ham club.

I saved the old T kits when I installed repeaters on sites with mux.

The last one that I tuned needed the yellow tee. I tuned it up with the existing green one, and it worked fine.

I think that the tee is not all that critical.

So if my station is already tuned up, I can reinstall the green banded tee (TX Low, RX high) on my TX high RX low station and it should work fine?

Interesting. Let me know on this.

My two bits worth:
The station MUST be aligned with the Tee cables in place.
The filters closest to the antenna port are very much influenced by the terminations.
This is why the manual must be followed as far as the terminations during alignment.
The idea is to get the filter to match the cable impedence so you get maximum power transfer.
This is why the cable length can be some what incorect in length and still overall meet spec. I don't know how far this can be streched.
Perhaps there will be problems further down the band.
Cables can be lengthened by the use of right angle connectors.
I tuned a station for the local ham club T449 R 444 with no problem with the green cable.
Note that this station is rated for 55W continuous.
The rating for a base is 110W.(no filters)

If you are concerned about frying something, turn the power down to 10W or so.

I am running the station at 60 watts. I am just going to end up reworking the green banded tee so that it is turned into a yellow tee.