* * * IC8POF's   RCS8Vantenna switch mod. * * *
substitution of the old relays with the VR311 vacuum ones and the oxidized SO239s.

rcs8v vr311 relays

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After many years of good work at my qth, a near marine enviroment, I have decided to substitute the old mechanical relays (still good)
and the SO239s due to their severe oxidation and the intermittent RF conductivity path ,

  Here comes this almost easy add-on story.

...this larger pic -> oxidized so239    shows the severe oxidation of the SO239s and the holding rivets
   that led to insufficient-intermittent connection between the connector's bodies
   and the holding ground plate.

 

 

 

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The rework is divided in two parts : Mechanical   and    Electrical .

  • Mec1): removing the old relays:  my first try was with an HOTAIR blower and a tin-sucker, but it gave no success
         due to the quantity of the original tin on the connections and some burns resulted in the pcb fiber.
     
     pcb empty    Much better work resulted in the use of a medium soldering iron (70-80W) and some pieces of the RG58 braid, which literally absorbs the heated tin when is put over it.

 

  • Mec2) Fitting the new SO239.

    •   due to the different height of the SO239 bodies, the new one have been mounted
         on the inner part of the holding plate to get the necessary height for the center
         soldering pin and the relays board.
       pic1
      so239 differenze      		  pic2 rcs8v so239

 

 

  • Mec3)   the SO239 holding plate, old view and the reworked one with the new connectors.

    • showing the placement of the new SO239s on the inner part of the plate due to the different dimensions,
         Every SO239 has three holding screws, instead of two, but not four due to some irregularities of the holding plate.
         The old pcb spacers&ground-posts have been left just for alignment purposes.
         The ground relay path has been routed via a new connection.
       pic1
      so239 prima e dopo      		  pic2 rcs8v pcb spacers


    • Mec4)
         All the contact points have been coated with the NOALOX paste.
         Due to the plate irregularities all the screws have been glued with the LOCTITE glue.
         At the end of the rework both sides have been painted with the transparent FLATTOP paint.
         The ground path (red dot) has been left clean to accept the ground point for the relay pcb.

       coat1 coated plate  coat2 coated plate 2   ground path rcs8v new ground

  • Mec5)   VR311 relays mounting hints .

       My solution to mount the new relays was to give them the right distance from the old pcb by adding a small piece of new pcb as spacer

    pic1 rcs8v old & new relais pic2 rcs8v vr311 spacers

       in this way the relays are held at the right distance to preserve the glass relay foot (red dot) protruding on the underside of the body,
       avoiding the difficulties to bend a ticker copper wire for the connections, and avoiding the cut of the old pcb tracks.

    pic3 vr311 pcb spacers pic4 vr311 pcb shoes


  • Mec6)   VR311 relays RF path connection .

       The original RF PATH schema leaves all the antennas in the OPEN\UNCONNECTED state,
       but not the ground coax braids and I have decided to follow that schema too.
       A future upgrade could be the add_on of the Gas_Discharge items.

    rcs8v rf schema old rcs8v rf schema new    anti RFI upgradeanti rfi


       The electrical RF path connection has been done by the means of 3 (out of 7 and if needed more can be added) x RG213 copper wires
       whose diameter is larger than the tiny pcb track; instead of a single ticker wire which would be more difficult to bend
      and keep the distances from the pcb, thus making the mounting phase easier.   

    ...this pic -> vr311 rf path connection    shows how the new relays feet are connected to the old pcb.

 

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   Electrical part, reworking of the PSU.



The original PSU schematic with a single diode could even be good, but the new transformator at almost 40Vdc out (1 diode no load)
could led to some too variable and unstable DC output voltage. To avoid this situation a small stabilizer is to be used.
The mounting of the transformator is done by the means of one isolating pcb, four feet for the trafo_pins and a 220vac fuse-holder.

rcs8v new trafo


The transformer used (24vac\117mA) has enough current, but resulting in an unstable and critical load voltage with one rectifying diode,
hence the use of a diode bridge is quasi obliged, as the VR311 relays require 26,5Vdc at nominal 80mA of current.

I thought to use an LM317 stabilizer, but the drop from 40V out of the single diode to 30-34Vdc of the diode-bridge on load
was not sufficient to stabilize the required 26.5V output.

Therefore I discussed about the use of this transformer and what sort of stabilizer could be used with my friend Gian I7SWX
and he has suggested to try the following schema :

   *** 24VAC trafo secondary output to a 4 diodes bridge + a transistor\zener stabilizer + the position led. ***.

new psu pcb ->rcs8v new pcb 26v the yellow dots show the pcb mounting posts in the psu-box.

  • The stabilizer uses a NPN transistor buffer in a classic schema to reduce output changes,
    •   the base is connected to a multiple diodes set-up :
          the 2 serial zener plus the 1N4148 deliver a voltage of around +-29 V,
          the led diode (green gives circa 1.7V reduction) connected to the base (further -0.7V) and the transistor Vbe
          give a resulting stabilized output at the Emitter of around 26.3/5V.
So I used what I had at stock and assembled the circuit as per schematic.
During the test phase I have discovered that not all the five relays had the same resistance but it ranged from 310 to 325 Ohm.
Of course the test has beeen carried with an in-lab 30 meters 2x0.34mm wires and the resulting total current drawn
from each relay ranged from 65 to 75 mA and summing the 10/15 mA of each position-led the total current is well
in the load range of the transformer used.

 original psurcs8v original psu  diode bridgercs8v diode bridge  stabilizer rcs8v stabilizer i7swx

Last note : the front panel led indicators must be checked for a good light indication at a 1.5 to 2 Vdc working condition
     against the dropping resistor, in my case about 4000 Ohm and the new 26.5 Voltage.
      I had to change two of them because did not light at all.



Of course the schema has worked well at once.
A big thankyou to my friend Gian I7SWX from the ideas and suggestions.  mods & improvements by I7SWX.

Any improvement or suggestions will be appreciated,
write to my email on ic8pofATyahooDoOTcom (copy,paste and correct)
.

 


© v 1.00 feb\mar.2022