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Big cans

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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mogman
Posts: 112
Joined: Tue Aug 05, 2008 2:25 pm

Big cans

Postby mogman » Sat Mar 18, 2017 7:42 am

I purchased a lot of VHF equipment and among the debris was three large VHF cans, obviously frequency pass but the curious thing is the loss, they have a pretty sharp curve but show to have 4.33db of insertion loss. these cans measure 11" IN DIA. and 24" tall (cans only)
I was going to add a picture because I would like to look up the specs but I cannot see how to add a picture, will look elsewhere

RFguy
Posts: 1258
Joined: Wed Dec 21, 2005 6:17 am

Re: Big cans

Postby RFguy » Sat Mar 18, 2017 8:08 am

Hmmm, I thought this post was going to be about something else. Sad

:)

User avatar
kb4mdz
Posts: 266
Joined: Tue Oct 02, 2001 4:00 pm
What radios do you own?: Too many for the time I have.

Re: Big cans

Postby kb4mdz » Sat Mar 18, 2017 10:21 am

no, talking about my sister-in-law's butt is not appropriate here, RFguy.

Jim202
Posts: 3457
Joined: Sun Sep 09, 2001 4:00 pm

Re: Big cans

Postby Jim202 » Sat Mar 18, 2017 11:11 am

mogman wrote:I purchased a lot of VHF equipment and among the debris was three large VHF cans, obviously frequency pass but the curious thing is the loss, they have a pretty sharp curve but show to have 4.33db of insertion loss. these cans measure 11" IN DIA. and 24" tall (cans only)
I was going to add a picture because I would like to look up the specs but I cannot see how to add a picture, will look elsewhere



That sounds like a higher than normal insertion loss. But unless your testing them at the frequency they are currently tuned on, the insertion loss can be high. Then again, someone might have messed with the tuning of the cans. The frequency is also dependent on the length of the cables between the cans. If it was re-tuned very far, from where the original cables were for, that will also effect the insertion loss. Lastly, if you look at the top of the cans, many of them have adjustable insertion. There might be a metal plate with with numbers stamped in it. This is the coupling loss.

Many people really don't know how to tune these devices correctly. One of the most important points to be concerned with is to make sure all the cable ports are terminated while tuning the cavities. By this I mean the RX port, the TX port and the antenna port.

I tend to use a 6 or 10 db attenuator on all the non terminated ports while tuning. Even leave them on while tuning so the adjustments don't get screwed up while you tune the cavities. I have seen radio techs chase their but and spend hours trying to tune the duplexer. I walk in, show them how to do it, and can be done in maybe 15 minutes.

I would get the model number off of it and try to see just what you have. They are not that hard to tune.

Jim

mogman
Posts: 112
Joined: Tue Aug 05, 2008 2:25 pm

Re: Big cans

Postby mogman » Sat Mar 18, 2017 12:39 pm

I am sweeping it with a tracking generator, tuned from 140-170MHz (actually tuning the can) the loss is the same, no other adjustments, input/output are on the sides of the can and fixed 180deg apart, no numbers or I would google it, color is that little bit darker than beige that some of the older Motorola equipment had, dual hand wheels on top to push up or down, about 3 1/2" in dia. tower that positions the rod is about 4" in dia. 6" tall with one side open to access the lower locking wheel, three large gussets supporting the tower.

mogman
Posts: 112
Joined: Tue Aug 05, 2008 2:25 pm

Re: Big cans

Postby mogman » Sat Mar 18, 2017 1:21 pm

I have only tested one of these cans, it will take several days to get to the front of the trailer where the other two are located, so there could be a defect in this can.

User avatar
abbylind
Posts: 507
Joined: Mon Nov 05, 2001 4:00 pm
What radios do you own?: What dont I own?

Re: Big cans

Postby abbylind » Sat Mar 18, 2017 5:00 pm

Darker brown color.....sounds like Sinclair cans..

Jim202
Posts: 3457
Joined: Sun Sep 09, 2001 4:00 pm

Re: Big cans

Postby Jim202 » Sun Mar 19, 2017 4:56 am

mogman wrote:I am sweeping it with a tracking generator, tuned from 140-170MHz (actually tuning the can) the loss is the same, no other adjustments, input/output are on the sides of the can and fixed 180deg apart, no numbers or I would google it, color is that little bit darker than beige that some of the older Motorola equipment had, dual hand wheels on top to push up or down, about 3 1/2" in dia. tower that positions the rod is about 4" in dia. 6" tall with one side open to access the lower locking wheel, three large gussets supporting the tower.


While sweeping the can, were you able to figure out if it is a pass cavity or a notch cavity? They do not work the same. If it is a notch cavity, you might miss the notch if your sweep was not narrow enough. Notch cavities can be used on both the TX and RX sides, so it would be hard to tell from how they are being used or cabled, if still installed in the system.

Jim

mogman
Posts: 112
Joined: Tue Aug 05, 2008 2:25 pm

Re: Big cans

Postby mogman » Mon Mar 20, 2017 1:14 pm

First I have never seen a notch cavity with two ports, not saying they don't exist but I have seen allot of cans and never a two port notch, second I swept it from DC to daylight, it is for SURE a pass can

DarkHelmet
New User
Posts: 26
Joined: Fri Mar 13, 2015 3:29 pm

Re: Big cans

Postby DarkHelmet » Sun Apr 16, 2017 6:55 am

Sound like pass cavities from a combiner. The coupling loops will determine the insertion loss/s21 and VSWR/s11. Rotate them to get the s21 down and couple more into the cavity. This will make the response of the cavity much wider though.

You can convert these to Bp/Br with adding a capacitor in series with the loop.


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