Monday, 27 August 2018

Variable-length phasing cables for tuning repeater duplexers: Part 2, Using the cable

Variable-length phasing cables for tuning repeater duplexers: Part 2, Using the cable (draft)

Introduction

In Part 1, a variable-length phasing cable for use in determining duplexer cable lengths, using M/F SMA connectors to vary the length is discussed.

In Part 2, this post, I will cover the use of the variable-length phasing cable in more detail.

say more??

The basic process

The basic process of using a variable-length phasing cable to tune a six cavity duplexer:

1/ Tune each cavity to frequency.

2/ Connect the three cavities with two same length adjustable phasing cables of approximately the right length

3/ Using a spectrum analyser and tracking generator or a vector network analyser (VNA), take out or insert SMA connectors in both cables until the desired response is achieved.

4/ Using a Tee connector between the ports of the instrument, measure the resonate frequency of one of the correct length variable cables as a quarter wave stub.

5/ Cut a length of cable a little longer than desired, attach one connector, connect to Tee and measure the resonate length. Cut the cable to that of the variable length cable.

6/ Attach the second connector and check that the resonate frequency is the same as the variable-length cable. Make a second phasing cable to the same length.

7/ Attach both new phasing cables to the duplexer and check the desired response is achieved.

8/ Repeat for the other side of the duplexer.


1/ Tune each cavity to frequency.

??

2/ Connect the three cavities with two same length adjustable phasing cables of approximately the right length

??

3/ Take out or insert SMA connectors in both cables until the desired response is achieved.

??

4/ Measure the resonate frequency of one of the correct length variable cables as a quarter wave stub.

??

5/ Cut a new cable of the same length. 

??

6/ Complete cable and check length.

??

7/ Attach both new phasing cables to the duplexer and check the desired response is achieved (repeat 2&3).

??

8/ Repeat for the other side of the duplexer.

??

Discussion

??

Conclusion


Sunday, 26 August 2018

Variable-length phasing cables for tuning repeater duplexers: Part 1, Construction of the cable

Variable-length phasing cables for tuning repeater duplexers: Part 1, Construction of the cable

Introduction

A variable-length phasing cable for use in determining duplexer cable lengths, using M/F SMA connectors to vary the length is proposed. It is a cheaper alternative to a set of phasing cables with a 10mm (5mm?) length increment.

This post describes the concept and how it can be replicated. A simple idea, but some frustration in execution. The basic process of using the variable-length cables is outlined.

The next post will cover the use of the variable length cables and include screenshots from instruments and photos.

The problem: determining cable lengths for inter-connecting duplexer cavities

Determining cable lengths for inter-connecting duplexer cavities is a perennial topic. Notionally, they are a quarter wavelength or odd multiple, allowing for coax velocity factor, but in practice that is a starting point.

My understanding is that commercially, a set of incremental length cables are used to find the correct lengths. Unfortunately, most people don't have such a set of cables.

An additional problem for a six cavity duplexer (3 RX, 2 TX) is that the two cavity inter-connecting cables interact, so both cables need to be varied in length at once to get a good filter response.

A solution: a variable length of coax!

A solution is a variable length of coax. My first attempt was to use M/F N-type connectors with short lengths of cable to change the length in 25mm increments. This was too coarse, giving a 10 MHz or more change in resonance as a quarter wave stub.

My second attempt was to incorporate a home-made sliding trombone joint, made of rolled copper shim for the outer, and small brass tubes for the inner. This gave a continuously variable length of 25mm to fit the gap using M/F N connectors. It works but is too stiff and delicate for practical use.

A variable length of coax using M/F N connectors and a home-made telescopic joint

My third attempt, and the one pursued, was to use SMA M/F connectors to change the cable length. The thin cable is flexible and the SMA connectors give an increment of about 10mm. Effectively, the increment is 5mm as the cable may be too long or too short, adding or removing a connector, where the optimum is half a connector length.

A variable length of coax using M/F SMA and N connectors


The variable length phasing cables are made up from M/F SMA connectors, N to SMA adaptors and SMA M/M pigtail cables. I used cheap Chinese parts to keep costs down; about $2 each. To make one general purpose cable, I suggest 10 M/F SMA connectors and two 100 and 200mm pigtail cables, plus the two SMA-N adapters. Double to make two cables as two cables are needed.

Purchasing the M/F SMA connectors was problematic as they are fairly scarce. More numerous are reverse polarity (RP) connectors. If the description has RP in it, it is the wrong type!

https://www.ebay.com/itm/SMA-adapter-SMA-Plug-male-to-SMA-Jack-female-RF-Coax-Adapter-connector-straight/151338805239?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

The ordinary purpose of M/F connectors was a mystery to me as the seem to achieve nothing. It seems their main use is as connector protectors on instruments. It seemed such a good idea that I used a few on my instruments. Connectors are only good for about 400 connection cycles, plus the problem of cross threads.

A M/F SMA connector, showing pin. There is a hole in the other end. Most on eBay are reverse polarity, RP types.
Subsequent to building the N type telescopic joint, I found via Google, that such joints are commercially available as an SMA adjustable phase trimmer. Oh to re-invent the wheel, again! But shows my thinking is on track. The only problem with such devices is the cost, about $200 and two are needed. Such a device could be used to give continuous adjustment for the 10 mm gap between the M/F SMA connectors, as per my telescopic N-type joint. However, I have not tried this device and don't know if it is the most suitable; make your own enquires before purchasing!

https://www.pasternack.com/adjustable-phase-trimmer-18-ghz-sma-10-deg-per-ghz-pe8203-p.aspx

SMA adjustable phase trimmer

Using variable length phasing cables

While the detailed procedure for using the cables will be covered in another blog post, with photos, the basic procedure to determine duplexer phasing cable lengths is as follows.

1/ Tune each cavity to frequency.

2/ Connect the three cavities with the two same-length adjustable cables, based on a calculation of a quater wave length (or odd multiple), taking into account both the velocity factor of the SMA cable and the length of connectors or Tee pieces on the cavities (assume the connectors are the same velocity factor as the cable). Roughly, 300mm for 2m using RG-214 between Tee connectors on cavities, 12mm less for N-type in-out sockets.

3/ Using a spectrum analyser and tracking generator or a vector network analyser (VNA), take out or insert SMA connectors in both cables until the desired response is achieved. Possibly (to be confirmed in next post), if the desired response is between an increment up or down in length, the desired length is half an SMA connector's effective length, about 5mm.

4/ Using a Tee connector between the ports of the instrument, measure the resonate frequency of one of the correct length variable cables as a quater wave stub. The frequency will be 10 MHz or so above the frequency of the cavity as to cavity connectors contribute to phasing cable length.

5/ Cut a length of cable a little longer than desiered, taking into account any difference with the SMA cable velocity factor. Attach one connector. Connect to Tee and measure the resonate length. Cut the length of the cable to increase the resonate frequency to that of the variable length cable (may need to allow a little for the second connector, to be confirmed, but will be small a couple of mm). If the length is between SMA connector increments, allow the 5mm or so (to be checked).

6/ Attach the second connector and check that the resonate frequency is the same as the variable-length cable. Make a second phasing cable to the same length.

7/ Attach both new phasing cables to the duplexer and check the desired response is achieved.

Conclusion

A variable-length phasing cable for use in determing duplexer cable lengths has been described, as an cheaper alternative to a set of phasing cables with a 10mm length increment. The cable uses M/F SMA connectors to vary the length.

The next post will cover the use of the variable length cables and include screen shots from instruments and photos.

Tuesday, 24 July 2018

3D printing UHF filters


3D printing UHF filters






https://all3dp.com/1/creality-ender-3-3d-printer-review/







Settings
https://www.youtube.com/watch?v=umulfK775i0


https://ultimaker.com/en/products/ultimaker-cura-software


https://ultimaker.com/en/resources/50296-which-material-should-i-use


Copper and silver plating
https://bryancera.blogspot.com/2014/09/copper-electroplatingforming-3d-prints.html
https://www.riogrande.com/category/tools-and-equipment/plating
https://janekits.com.au/products/copper-mix-inc-cumac-4-ltrs/
http://www.vitec.com.au/shop-online/pat-coleby-minerals/copper-sulphate

https://www.finishing.com/111/72.shtml
https://www.eevblog.com/forum/manufacture/my-way-to-professional-prototype-at-home/25/
https://www.thinktink.com/stack/volumes/voliii/consumbl/cplatmix.htm
https://www.thinktink.com/faqs/cupltfaq/cupltf01.htm












HP AGILENT 8935 E6380A RF TEST SET


HP AGILENT 8935 E6380A RF TEST SET

Service Monitor for HF and 2 way radio. They all generate AM, FM and have a calibrated output signal generator, have 2 separate audio tone generators, have 2uV sensitive "off the air receivers" with antenna input, encode/decode standard tone (PL) (CTCSS), have sinad, distortion, S/N meters, receive AM, FM and SSB, have modulation / deviation meter, frequency error meters.





Overview and screens for HP 8935 E6380A
http://www.amtronix.com/e6380a.htm


Comparison with other HP test sets
http://www.amtronix.com/diff.htm



All manuals available through Keysight, just search E6380.

Sunday, 15 July 2018

Commercial low power UHF DVB-T pass-band/notch filter

Commercial  DVB-T pass-band/notch filters: What we can learn

Introduction

Low power, UHF and VHF DVB-T pass-band/notch filters are commercially available at relatively low cost, ~US$750 that seem suitable for DATV. They seem a good off the shelf solution.

By examining such filters, it seems possible to see how they might work, giving some insight into possible home-brew.

The filters have two notch filters, one for each side of the signal, as per my earlier posts, to notch the TX skirts.

In addition, they have cavity pass-band filters to take out artefacts further out. A manufacturer indicates that the pass filter is a combline, but the mechanical construction suggests cavity filters with openings between cavities for coupling.

It seems possible to separate the notch and band-pass filters. For wideband UHF, two notch cavities and a pass-band filter. For 2m, two notch cavities and a single pass cavity may suffice.

Low-pass filters are still needed for odd harmonics in addition to a DVB-T filter.

Commercial filters DVB-T (UHF and VHF)

The UHF first commercial filter seems to have five band-pass cavities and two notch cavities, one at either end. The input, notch and first pass resonator seem to share the same cavity, similarly for output. Three of the resonators are in individual cavities. On the top, RHS of the filter are the resonator tuning knobs.

 http://www.com-tech.it/products/cl-series-c/




From the response curves, the two sharp notches are evident to filter the skirts. This is similar to what I found in earlier posts on notch duplexers for DVB-T. However, one pair seems sufficient, something I have been working on, rather than 3 pairs in a duplexer.

How the notches work is not particularly evident. The connector has a loop coupling per the manufacturer's claim of DC to earth for lightning protection. There is a protrusion on the opposite side of the connector, the purpose of which is not evident. The notch and first pass-band resonator seem to be in the same cavity. Each resonator may be energised, one as a notch, the other as the first resonator of the pass-band filter.

The response shows the five minimums in SWR from the five cavities. The pass-band is shown without ripples, which seems a bit optimistic.

The response also shows the filter losses, less than 1 dB according to the specifications; quite remarkable!



The filter is meant to be a combline, presumably similar to the diagram from Piette 2010.


However, the cavities seem to have openings between them as the line of screws do not go all the way. It would seem to be similar to the band-pass filter from Piette 2010. It is not clear from the first drawing if there are screws to adjust coupling, but there seems to be another adjustment next to the resonator tuning.

From the mechanical design, it does not seem to be an inter-digital filter.


The filter is quite small,

Third harmonic?

Size Power


http://www.com-tech.it/products/cl-series-c/
http://www.com-tech.it/glossary/xline/
http://www.sira.mi.it/en/products/broadcasting/8/uhf-dtv-filters/287

http://www.microwavefilter.com/FCC_Repack.html
http://www.sira.mi.it  http://nintermedia.com/pdfs/tv/CTV-V-DVB-025.pdf

Homebrew DVB-T TX filter?



http://www.ocicom.com/index.php/amateur-radio/products/440-mhz-bandpass-filter
Bernard Piette 2010 VHF/UHF Filters and Multicouplers: Applications of Air Resonators










Wednesday, 11 July 2018

450 MHz CDMA duplexer tear down and analysis


450 MHz CDMA duplexer tear down and analysis- draft

Introduction


Why?

I am interested in how modern duplexers work. The club purchased a new 70cm duplexer, only 50 mm tall and not obvious how it worked, but they didn't want me opening it for a look!

I purchased a CDMA duplexer from Russia on the 450 MHz band on eBay. It was similar to the 70 cm one. I could get some idea how the UHF one works and some(?!) chance of re-tuning it for either a 70 cm DVB-T TV filter, 7 MHz bandpass, or as a 70 cm narrow pass band repeater duplexer (or both, as there are three chains of seven cavities in the device.

Unfortunately, I did not take photos of the duplexer's response before I opened it. However, it was a 6 MHz pass band, with steep skirts, and low pass in the 450 MHz band. I will do it when I put the top back on, but have probably disturbed the tuning. CDMA signals are 1.23 MHz wide, so it is unclear why the pass band is 6 MHz.

The outside, with a zillion screws out. The left three connectors are all SMA, the right are 7/16 DIN and N adaptors that I added.

The gizzards!

Click photo to see captions larger!!


It is a complex beast, requiring a very detailed examination to see all its features. Pore over the photo to see.

?? = I think!

The duplexer has three chains of cavity filters, RX (top), RX monitor (middle) and TX (bottom). RX has its own antenna. TX and RX monitor share an antenna, but are on different frequencies. Tx input is to left. The resonators use big capacitive hats to electrically shorten the resonator to one rack height, otherwise four rack high. The resonator adjustment screws are the larger screws.

The filters are pass band and low pass. The low pass comes from the capacitive tuning into the resonator??

The filter chains are pass-band, iris-coupled (port-tuned) filters that have a sharp cut off. The iris-coupling screws are the smaller screws. In addition to iris-coupling, both inductive (on lid) and capacitive inter-cavity coupling are used. I don't know why, presumably to get a sharper response (or impedence matching??). There are no notch filters, as are used in DVB-T filters, to get a very sharp cut at the edges of the pass band.

The input/output are either a separate smaller resonator with a gamma match?? coupling (left), or a conventional gamma match?? coupling direct to the main resonator (right).










Sunday, 8 July 2018

Rohde & Schwarz CMU200 Universal Radio Communication Tester resources

Rohde & Schwarz CMU200 Universal Radio Communication Tester resources

Introduction

This post is a collection of information for the Rohde & Schwarz CMU200 Universal Radio Communication Tester that I have purchased. They can be bought on eBay and other places often for a very reasonable sum. In its day it was an expensive but capable instrument.

While the CMU200 is primarily designed for testing now obsolete mobile phone equipment, it can be used for working with analog radio. It has a spectrum analyser, RF generator, RF power measurement and with the option, an audio test set. While not directly having a tracking generator function, there are two PC programs that allow it to be used for testing filters. It can also be done with a noise source or an external tracking generator.

The CMU200 uses an embedded Celeron or similar AMD processor running MS-DOS. It has an internal IDE HDD that is wise to replace as the instrument can do tens of thousands of hours. An IDE SSD allows the instrument to boot much faster.

Documentation is available from R&S. The CMU200 is discussed often in the eevblog forum.

The CMU200 can be used with a PC via a GPIB USB adaptor. There is R&S and third party software that increases the instument's functionality.

I have compared a duplexer response with the CMU200 and Siglent SSA3021Z with a $20 noise source and the Siglent's tracking generator.

My machine while replacing HDD, yes that is it on the top. The screen is dimmed around the edge presumably from curling of reflector around fluro tube. Will fix/replace. Screen is spectrum analyser showing local DVB-T TV stations. Nice!

Resources

Search "CMU200" in:
https://www.rohde-schwarz.com/us/home_48230.html
https://gloris.rohde-schwarz.com/anonymous/en/pages/toplevel/home.html?    must register (free)
https://www.eevblog.com/forum/index.php
https://www.mikrocontroller.net

Replace HDD with SSD

My analyser had its original HDD c2000 with 35000 hours. As such I was keen to back it up and replace it. No trouble extracting HDD or backing it up. I unsuccessfully tried the Kingspec drive as per below, but the drive was not recognized. I did the same with an old 20GB HDD from a laptop and that worked fine. My analyser uses earlier AMD CPU and older BIOS. That may be the difference? Cute using PS2 keyboard on an instrument to do MSDOS.

cut and paste from eevblog forum in italics

"The HDD-Raw-Copy-Tool tool does a sector by sector copy of the entire drive. The resulting RAW image can be opened by a tool like PowerISO and this what I used to upgraded the CMU200 DOS software.

Both the CMU200 Celeron and CRTU-RU Pentium III boards have worked with various Fujitsu 20GB and IBM 30GB IDE drives I have connected.  BIOS has autodetected all OK. I have replaced the CMU200 drive with Kingspec PATA IDE 2.5" 32GB SSD and again HDD-Raw-Copy-Tool was used to write the image to the drive before installation. Now the CMU200 boots like a rocket.

I note the Award BIOS FLASH tool and bios image can be found in \internal\install\bios folder. Run the batch file FLASH.BAT to reflash."



"1) remove the hard drive from the CMU, and attached is to a device like this: http://www.dx.com/p/unitek-y-3321-usb3-0-to-ide-sata-hard-disk-drive-hdd-docking-converter-black-230128

2) made an exact image of the drive to a file with this software: http://hddguru.com/software/HDD-Raw-Copy-Tool/ (I used the portable version to avoid installing the software)

3) removed an IDE harddrive from a back-up USB drive I had lying around (the HD in my CMU was a 20GB one, but I replaced it with a 40GB one without any issues

4) restored the image from the file to the "new" HD using the same software as in step 2"

Screen fix: LCD & EFI glass

LCD fix or replace

The screens can fail or go dim. A dim screen seems to often be just the reflector curling around the tube. The tube back-light can be replaced with LED strip.
Detailed fix:  http://www.rbarrios.com/projects/LCD2LED/
https://www.eevblog.com/forum/repair/rohde-schwarz-cmu200-lcd-backlight-success/

It seems possible to replace the screen with a new one. The screen seems to be a Sharp LQ084V1DG21  They are on eBay for US$100+. I have ordered one and will replace it when it arrives, with a report here. Main trouble with mine was EFI glass.

PDF: https://www.mouser.com/ds/2/365/LQ084V1DG21_SP_071305-184349.pdf
Graphic LCD Display Module Transmissive Red, Green, Blue (RGB) TFT - Color Parallel, 18-Bit (RGB) 8.4" (213.36mm) 640 x 480 (VGA)

EFI glass

The EFI glass commonly discolours. It was the main problem with my CMU200. Removing the glass fixed the problem, but getting a replacement EFI glass is a problem, but looking. The screen is still a little dim and I will replace it.

Manuals

Operating, quick start and service manuals:
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/sr001Man?OpenDocument

manufacturer page:

https://www.rohde-schwarz.com/en/product/cmu200-productstartpage_63493-7830.html

and the brochure:
https://cdn.rohde-schwarz.com/pws/dl_downloads/dl_common_library/dl_brochures_and_datasheets/pdf_1/CMU200_bro_en.pdf

Detailed specifications:
http://www.upc.edu/sct/documents_equipament/d_175_id-448.pdf

Service manual:
https://www.ntecusa.com/docs/RS_CMU200_CMU300_other.pdf

Drivers
https://www.rohde-schwarz.com/us/driver/cmu200/

Firmware

Only the most recent firmware seems to be available from R&S. Earlier versions seem to have expired. Probably a good idea to keep a copy of current firmware before updating. May be a good idea not to update if little extra functionalityis added. See firmware text file for earlier versions.

CMU200 last firmware downloadable via R&S GLORIS account (picture is screen shot from GLORIS not links). Other links are below.

Base 5.21 firmware
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/SR001Z?OpenDocument
CMU200_GSM_5.22
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/SR003Z?OpenDocument
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/SR004Z?OpenDocument
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/SR006Z?OpenDocument
CDMA 2000 MS 5.20 package is here :
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/sr009z2?OpenDocument
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/sr015m?OpenDocument - manual
http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/sr015Z?OpenDocument - install

http://www3.rohde-schwarz.com/www/FileTranCS.nsf/alias/DATS?OpenDocument - It is PC part of CMU-K92 option, GPRS application testing package. Manual is also there.




All new firmware?
http://gotroot.ca/cmu200/

Text file from eevblog?
https://www.mikrocontroller.net/attachment/337287/EEVBLOG_CMU200.txt

R&S software

CMU200 Software- CMUgo- Remote control software
https://www.rohde-schwarz.com/au/software/cmu200/

RSCommander
https://www.rohde-schwarz.com/de/applikationen/rscommander-flexibles-software-tool-fuer-instrumente-von-rohde-schwarz-application-note_56280-15410.html

The free software FreRes from Rohde & Schwarz allows to make sweep and test for example filters or duplexers.
https://www.rohde-schwarz.com/us/applications/freres-program-for-frequency-response-measurements-application-note_56280-15551.html
https://www.keysight.com/upload/cmc_upload/All/readme_IOLibraries_18_1_22603_1.htm?&cc=US&lc=eng

Third Party software

http://vma-satellite.blogspot.pt/2018/03/vma-simple-spectrum-analyser-for-crtu.html
https://vma-satellite.blogspot.com/2018/06/remote-control-of-r-cmu200-and-crtu.html
https://vma-satellite.blogspot.com/2018/03/vma-simple-spectrum-analyser-for-crtu_24.html

My unit

Serial Number: 10133X, X=bd-23
Options
CMU-B11 (HW): Reference oscillator OXCO, aging 2 X 10E-7/year
CMU-B12 (HW): Reference oscillator OXCO, aging 3.5x10E-8/year
CMU-B21 (HW): Universal signalling unit CMU-B21V14 incl. CMU-B54
CMU-B41 (HW): Audio Generator and Analyzer
CMU-B83 (HW): CDMA2000® signaling unit (requires R&S®CMU-U65)
CMU-U61 (HW): PCMCIA
CMU-U65 (HW): Upgrade kit for CMU200: Measurement DSP module for measurement speed improvement
CMU-K29 (SW): Analog AMPS, for CMU-B21, CMU-B41 required V5.20
CMU-K84 (SW): CDMA2000 (cellular band) for CMU-B83 V5.20
CMU-K85 (SW): CDMA2000 (PCS band) for CMU-B83r V5.20
Hardware
Front Module: FMR5
CPU: AMD K6-III
Memory: 128 MB
Firmware: V8.50 02.05.06

Duplexer tuning

A duplexer response with the CMU200 and Siglent SSA3021Z with a $20 noise source and the Siglent's tracking generator, respectively. The tracking generator is best, not surprisingly, but the noise source with the CMU200 is quite usable. Adjusting for insertion loss would be awkward. A noise source avoids needing a PC to run the tracking generator in the CMU200.





VMA simple spectrum analyser/remote-control-of-r-cmu200

I tried out VMA's spectrum analyser software with a Agilent 82357B USB GPIB adapter and the . Needed to read the instructions, but easy enough to get going. Works nicely, giving a waterfall to the CMU200 spectrum.

The Keysight IO control package screen


VMA's spectrum analyser screen shot showing waterfall and eight local DVB-T free to air channels. Nice!


The CMU200 screen set as per the last VMA photo above (with EFI glass removed, no brown edge, but still a bit dim)