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informatie pagina voor experimenteel radio-onderzoekers

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  Item Philips PM2524 multimeter
  Item Rigol DS-1054Z
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 Racal Cougar
  Item 0. Racal Cougar
  Item 1. introduction
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  Item Trimble 34310-T OCVCXO
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  Item test- en meetapparatuur

  Item Counter 1 MHz input mod.
  Item Yaesu FT-897/FT-897D
  Item Yaesu MH-48 lock mod

  Item (coax) kabels coderen
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  Item Lineair 400W (Frinear)
  Item MFJ-948 antennetuner
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  Item Tinytrak 4
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  Item voedingsconnector FT-897
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  Item Yaesu FT-857/897 meter
  Item zwaai Alinco DR-135E MkII

  Item elektromigratie in filters

  Item Ameritron ATR-20 tuner
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  Item Yaesu FT-101E
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  Item capacitors
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  Item Kenwood TS-830M
  Item Lorenz SEM25
  Item Yaesu FT-897D

 Rigol DSA815-TG
  Item meting: omroepband
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  Item elektret microphone
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 surplus apparatuur
  Item Bosch Condor 16
  Item Motorola GM950 (70 MHz)
  Item Rohill R-2050

 telefonie surplus
  Item Ericsson F-955
  Item Ericsson F-955 modifcations 2017
  Item Ericsson RS203/RS2062
  Item Nokia NCM30
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  Item Nokia RD72
  Item Radiosystem monitoring unit
  Item Radiosystem RS922
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  Item Radiosystem RS951
  Item Radiosystems RS963
  Item Radiosystems RS9694
  Item RS925 service box

  Item aarding
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  Item circulator/isolator
  Item snubber diode

  Item Minipro TL866 programmer
  Item Velleman VTSSC50N soldering iron
  Item Yihua 852D+ soldeering station
  Item ZD-409 desoldering tweezer
  Item ZD-915 desoldering station

  Item soldering
  Item workshop tips

  Item decoupling capacitors

  Item Beryllium oxide
  Item EM veldsterkte
  Item radioactiviteit
  Item harardous radioation?

  Item SV500

Yaesu FT-897/FT-897D

SSB TX backgroiund noise problem and solution permalink:
Many FT-897 users report bad transmitted SSB/CW audio since "birdies" are heard if the DSP MIC EQ (menu item #48) is switched on. The modification information is found on the internet at different sources. The transmitted audio signal is fed trough the AK7712VT DSP procecessor unit; chip Q1092. The groundplane of the DSP processor unit is connector to the ground of the rest of the rig trough inductor L1059 (10 uH) in the green package marked "10N". It is said that the digital and audio ground should be seperated, but this is not in the FT-897 mainboard design. It's likely the clock signal of the DSP processor causes the noise on the transmitted audio signal due to different ground paths. The solution is quite simple. Inductor L1059 should be "bridged" connecting the "local DSP ground" to the common ground of the rest of the circuit. (It's also said that the FT-857 rigs do have a common ground for all the DSP signals, but I wasn't able to verify this.)
After removing the mainboard I scratched the paint of the circuit board and soldered the two groundplanes together. The result is shown on the image below. The tricky thing is to remove and replace the mainboard from the rig without causing collateral damage...

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flickering squelch problem and solution permalink:
The FT-897 has "flickering" squelch behaviour in standby mode. Even if there's no (weak) signal, the squelch opens for a short amount of time. This flickering me anoying and this could be solved by adding a capacitor to the mainboard. I read about this solution described by Jochen; DG2IAQ. Jochen discovered that the original 0,47 uF SMD capacitor is too small for stable squelch operation. SMD capacitor C1336 is marked "E474". To solve the flickering squelch problem, add one 4,7 uF electrolytic capacitor in parallel with existing capacirot C1336 . The C1336 capacitor is located between the DATA and ACC connector on top of the mainboad. The negative side is near the back end of the radio. Jochen; DG2IAQ assured 4,7 uF is the right value since he performed several test on this. The squelch should perform much better/sharper, the squelch level is the same as before, weak signals are detected better and more stable and the flickering is gone. So don't worry, no weak signal will be missed. The modification will add some delay after closing the squelch, but won't be noticable unless a before/after comparison is made.

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I performed the modification as described and I can tell the performance of the rig improved a lot. The squelch is much more stable and I would recommend performing this modification. I made an image of my rig with the added capacitor which is shown above. With some smd soldering skills (and patience), this modification is quite easy. The tricky part is removing the mainboard from the radio. Take your time performing the modification and beware not to damage the white flatcable. Remind that the exciter heatsink and driver requires new thermal paste for conducting heat to the metal housing. If your not familiair with smd soldering or not skilled in this area, maybe Radioamateurshop (located in The Netherlands) can help you out.

MARS/CAP modificatie permalink:
De betreffende FT-897D is blijkbaar ooit gemodificeerd met de bekende MARS/CAP modificatie. Met de MARC/CAP modificatie kan de FT-897/FT-897D buiten de banden zenden. Bijvoorbeeld ook op de 5 MHz band. Let er wel op dat je niet per ongeluk buiten de amateurbanden gaat zenden! De modificatie is in dit geval buitengewoon slecht uitgevoerd. Er zijn twee stukken draad op de eilandjes "geplakt" en de klodders tin zaten aan omringende zes pins chips. Om de eilandjes was een brei van zwart hars zichtbaar, blijkbaar is er een vieze (te grote) soldeerbout gebruikt voor de modificatie. Tot mijn grote ergernis is de foto van dit flanswerk helaas verloren gegaan. (...) Gelukkig is dit slagveld prima te herstelen! De draden zijn met behulp van een stereo microscoop verwijderd, en het oude hars is met een tandarts "sonde" mechanisch verwijderd. Met 70% Isopropyl alcohol is de print gereinigd. Met vloeibare flux en desoldeer litze zijn de eilandjes netjes vrijgemaakt van overtollig soldeertin en de omringende klodders tin zijn verwijderd. De eilandjes 7 en 9 zijn met een druppel tin verbonden. (Eilanden 6 en 8 zijn origineel al met een "nul Ohm weerstand" overbrugd.) Na het solderen is wederom met alcohol en wattenstaafjes de flux en hars verwijderd totdat er een schone print overbleef. De foto van het eindresultaat is hieronder afgebeeld evenals een afbeelding van de locatie van de "jumpers". let op de opmerkelijke volgorde van de jumpers in relatie met de nummers. De witte letters naast de jumpers geven het juiste nummer aan. Voor een volledige buiten de band modificatie dienen alleen jumpers 6, 7, 8 en 9 te zijn verbonden. De overige jumpers dienen niet overbrugd te zijn.

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