Author Topic: Teardown: Kathrein GSM900 base station sector antenna (Read 15244 times)

wkb · « **on:** February 27, 2016, 10:45:03 pm »

Today I visited a ham-fest to gain some much needed (....) parts & 'stuff'. One of the things on my shopping list was some semi-rigid coax.
As it turned out, no loose semi-rigid was to be found.

What I did find and what had ample semi-rigid was a Kathrein GSM900 cell base station antenna. Which changed hands for the princely sum of EUR 5. Me dragging it out of the building gave rise to to more than few raised eyebrows

After muttering some niceties because it only just fitted in the car I took it home.

Picture series shows the teardown of this antenna. This particular version has separate 7/16 connectors for connection to the horizontally and vertically polarised antenna. Construction is very solid Deutsche GrÜndlichkeit: stainless steel bolts, silvered connectors, tons of pop rivets to obtain a very rigid construction etc. The Kathrein catalog promises 15 years of maintenance free operation. As can be seen extensive lengths of semi-rigid, or more exact Huber & Suhner Sucoform 141. The cables are connected via soldered-on 'junction boxes'. The white blocks are plastic spacers.

wkb · « **Reply #1 on:** February 27, 2016, 10:49:23 pm »

More pictures

wkb · « **Reply #2 on:** February 27, 2016, 10:50:47 pm »

Yet more pictures

wkb · « **Reply #3 on:** February 27, 2016, 10:52:10 pm »

And a bit more pictures, one with part of the wiring

wkb · « **Reply #4 on:** February 27, 2016, 10:59:42 pm »

wkb · « **Reply #5 on:** February 27, 2016, 11:02:04 pm »

wkb · « **Reply #6 on:** February 27, 2016, 11:03:16 pm »

Coax plumbing

wkb · « **Reply #7 on:** February 27, 2016, 11:06:39 pm »

more plumbing

wkb · « **Reply #8 on:** February 27, 2016, 11:10:05 pm »

The harvest: a considerable amount of semi-rigid

HAL-42b · « **Reply #9 on:** February 27, 2016, 11:20:32 pm »

So both vertical and horizontal polarization. Didn't know that.

wkb · « **Reply #10 on:** February 27, 2016, 11:28:48 pm »

Quote from: HAL-42b on February 27, 2016, 11:20:32 pm

So both vertical and horizontal polarization. Didn't know that.

Well, some antennas at the ham-fest had both H and V, some only had V ( I think it was).

I grabbed the dual H/V given that it contains more coax

wkb · « **Reply #11 on:** February 28, 2016, 07:00:08 pm »

Some detail pictures of the individual dipole elements. They are directly fed with 75Ohm Sucoform semi-rigid. Note everything is at DC ground. The elements are made of solid copper, judging from the edges where they were cut. The copper is tin(?)-plated which makes for the non-copper appearance.

Aside: I found 3 (at least) impedances of the Sucoform were used: 75 Ohms, 100 Ohms, and 50 Ohms. Not all of it is clearly marked unfortunately.

SeanB · « **Reply #12 on:** February 28, 2016, 07:55:27 pm »

So that is what was inside the old ones on the roof. they were replaced last year with new ones, as the carrier is migrating away from GSM900, so there are some GSM1800 and UTMS steerable antennas there now. All connected with corrugated rigid line down to the base station on ground level.

I think the old Kathrein ones were sold off to another carrier building out a network, which uses GSM900 in low density areas for the improved coverage, and that most of the customers in those areas also are low bandwidth users, mostly using voice and SMS, or GPRS data.

PE1RKI · « **Reply #13 on:** February 28, 2016, 09:48:49 pm »

i dismantled also one, i managed to snag this one from many 100's of these that all got scrapped. all unused, from unopened new boxes.

luckaly all the semirigid inside was 50 ohm. inside was very different to yours.
here is a link to my flickr album of the antenna https://www.flickr.com/photos/pe1rki/albums/72157643213030984
it even had tuning for elevation or something and lasercut brass airlines with different kind of impedances for stacking the antenna's i guess.

daqq · « **Reply #14 on:** February 29, 2016, 09:52:01 am »

Thanks for the pics!

wkb · « **Reply #15 on:** February 29, 2016, 03:28:01 pm »

Quote from: PE1RKI on February 28, 2016, 09:48:49 pm

i dismantled also one, i managed to snag this one from many 100's of these that all got scrapped. all unused, from unopened new boxes.
luckaly all the semirigid inside was 50 ohm. inside was very different to yours.
here is a link to my flickr album of the antenna https://www.flickr.com/photos/pe1rki/albums/72157643213030984
it even had tuning for elevation or something and lasercut brass airlines with different kind of impedances for stacking the antenna's i guess.

Very different indeed! It contained sufficient 50R semirigid for what I want to build (RLB to go onto the SA). Would have been nicer to have all 50R but hey..

Wilko

PE1RKI · « **Reply #16 on:** February 29, 2016, 06:23:06 pm »

it was all habia cable flexiform 402 nm hfi 100.
50 ohm according to the datasheet.
i dont know how much you need but i can miss a piece of 40cm

wkb · « **Reply #17 on:** March 01, 2016, 11:44:14 am »

Quote from: PE1RKI on February 29, 2016, 06:23:06 pm

it was all habia cable flexiform 402 nm hfi 100.
50 ohm according to the datasheet.
i dont know how much you need but i can miss a piece of 40cm

Thanks for the offer! I have 2 pieces approx 60cm each of what should be 50R. After all they were connected to the 7-16 connectors.

Not yet sure what I will do with the 75 and 100 ohms Sucoform. tweedehands.nl comes to mind

maybe someone can make good use of it.

wkb · « **Reply #18 on:** March 01, 2016, 06:48:28 pm »

Today I decided I want to see if I can use a chopped-off part on 23cm. So I shortened the aluminium base. Not the dipole elements yet. The chopping resulted in picture #1 below.

After remounting 2 dipole elements I noticed that the vertical and horizontal dipoles have different dimensions, see picture #2
Most likely that is because the elements now mounted on the base protrude over the edge of the base. So Kathrein have tuned this carefully (obviously..

, this is a leading aerial manufacturer after all!).

So now I have to figure out how to join the 2 dipoles and ensure a 50R coax connection (using that interesting set of junction boxes and different impedance semi-rigid pieces). Now how did that work again, coax impedance transformation..

PE1RKI · « **Reply #19 on:** March 02, 2016, 01:44:08 pm »

you can use the 75 ohm coax now.
and make it like the wilkinson combiner but without the resistor.
2 pieces of 1/4 lambda coax splitting of to each antenna.
between antenna and the 75 ohm coax you can use 50 ohm again if the 75 ohm is to short.
it must be 70.7 ohm but i guess it will work ok with 75 ohm to.

wkb · « **Reply #20 on:** March 02, 2016, 03:47:42 pm »

Like the one in the picture? The dipole elements still have the
original 75R coax in sufficient length attached to them for 1/4lamba
@23cm I think

PE1RKI · « **Reply #21 on:** March 02, 2016, 03:49:49 pm »

yes!
the 75 ohm lines are also shortened by the velocity factor.

wkb · « **Reply #22 on:** March 02, 2016, 04:27:36 pm »

Quote from: PE1RKI on March 02, 2016, 03:49:49 pm

yes!
the 75 ohm lines are also shortened by the velocity factor.

Sucoform 141-75 datasheet tells me the VF is 71% ehh 0,71 so that helps
even more. The antenna in its original incarnation had these nice little
junction box so I can re-use those.

To what extent is the distance between the dipole elements of influence?
Sofar have not found too much on how these antennas are designed.

wkb · « **Reply #23 on:** March 02, 2016, 04:47:03 pm »

,just spent some time staring at pictures of the original coax harness. And noticed that the long type dipoles have different length coax between the junction box and the dipoles forming a pair.

Any suggestions?

PE1RKI · « **Reply #24 on:** March 02, 2016, 05:25:51 pm »

different frequency? maybe transmit and receive frequencies ?
the size is so different, it doesnt make sense.
best step forward is to put the antenna's individually on a network analyzer.


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Author Topic: Teardown: Kathrein GSM900 base station sector antenna (Read 15244 times)

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