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[G3TTC]

I’ve been using a 6-way RatPak unit to switch the feeder to one of 5 elements on my 5-band quad. It is mounted in an almost-waterproof plastic box on the boom. It has worked well for 4 years but now has failed. On inspection it seems damp has got to the relays. There are signs of rust on the armature and they are reluctant to move. Is this normal? Is there a US version with vacuum relays?
Keith G3TTC

[W1VT]

These appear to be standard OMRON relays.  I would just replace them.

I've tried several weatherproofing techniques.  One is mount the relays under a weatherproof roof that allows water to drain out the bottom.
The other is to heat the box to prevent water from condensing inside the box.  Just by running electronics continuously to generate heat.

Zak W1VT

[K5LXP]

Typical non-sealed relay spec:

Ambient temperature   Operating: -40 to 60°C (with no icing or condensation)
Ambient humidity   Operating: 5% to 85%

I wouldn't want to heat an outdoor enclosure like that unless it was plugged into my neighbor's garage.  A weatherproof NEMA-style box and a container of desiccant can do a pretty good job keeping the environment in check.

Mark K5LXP
Albuquerque, NM

[KL7CW]

Bring all cables into the bottom of the PVC ? enclosure.  Seal the sides and top of the enclosure.  Provide some small )1 mm ?) holes in the very bottom of the box.  It is impossible to seal any box completely, so condensation must have a way to get out.  In most situations this should do it.  In extreme situations sometimes a few watts of heat are used which may lower the humidity a few percent and prevent condensation.  Sometimes just running current through one or two relays all the time may be enough for reasonable size enclosures.  In 67 years I have not usually needed heat for my ham projects.  In very wet or marine environments heat may be extra insurance.  Sometimes I have used fine screen in the bottom of a box.  Sometimes if I needed to bring coax into the side of enclosure, I used a 90 degree elbow, and made sure the coax connector was well up inside the bottom of the elbow.  A few times commercial sites, a small amount of heat was used in a large box, probably less that 10 watts, to prevent condensation.
   Just ideas to think about,    Rick  KL7cw   

[KL7CW]

My favorite way to bring cables into a PVC electrical box is to glue several couplings to the bottom of the box.  Then run a hole saw up through the coupling into the box.  I often used couplings with 1 inch ID and a one inch hole saw.  My low band array uses about a dozen of these boxes, with several dozen ethernet cables running up from the bottom.  I believe some boxes have up to 3 couplings glued to the bottom, with several cables running into most couplings.  I just stuffed fiberglass (glass wool) into each coupling.  Seems to keep the very small bugs out so far ( 5 years ), and no trouble noted with condensation, but more bottom openings, like a screen on one of the couplings, might be better, since my fiberglass barrier might trap moisture.  I live in a cold Alaska climate 40 miles from saltwater, so this may not be a perfect solution since rust will be a bigger problem in warmer areas with heavy rainfall.  I have used many open frame relays for 53 years in Alaska, and rust corrosion does not seem to be a problem if the enclosure is vented so moisture can escape.  I glue the couplings to the bottom of the box, that way the low point inside the box is where the hole is.  Get an electrical box without inside ridges in the box  (I believe CARLON) is the brand I use in the US.
The couplings are probably 1.2 to 2 inches long, thus blowing snow, rain, sleet, etc. not likely to get up inside the box. These simple boxes are also inexpensive here in the US.  I think less than $ 10, but with inflation who knows.  I do not like any coax connectors outside the box, but prefer to have the connector inside the box if possible, but at least on the bottom, or as others sugested under a "roof" outside the enclosure.          Rick  KL7CW

[VE7RF]

Typical non-sealed relay spec:

Ambient temperature   Operating: -40 to 60°C (with no icing or condensation)
Ambient humidity   Operating: 5% to 85%

I wouldn't want to heat an outdoor enclosure like that unless it was plugged into my neighbor's garage.  A weatherproof NEMA-style box and a container of desiccant can do a pretty good job keeping the environment in check.

Mark K5LXP
Albuquerque, NM

One method is to use a sealed box..with drain holes / screening, to allow condensation out.

Method #2 is to use a NEMA, gasketed, waterproof box, and apply Permatex dielectric grease to the gasket, then close it tight.  Then LOAD the inside up with desiccant / silica gel. Then RTV everything on the outside of the box, so water / condensation can't get in.  Some resistance heat can also be used in fall/winter, to keep the inside of the nema box warm. Desiccant / silica gel will absorb 40% of it's weight in water. We used loads of it at the telco I worked for. Everything inside is bone dry.  Desiccant was changed out once per year on spec, but those were large cabinets too.

In some cases we would use compressed nitrogen, and just a few psi. 2 x SS bicycle style valves used. 1st one was opened up....while nitrogen pumped in under pressure via valve #2....allowing the existing air to be flushed out. Valve #1 closed, which allowed the cab to pressurize.  O ring replaced and new one re-greased once per year. 

The next hb remote ant switch box I'm going to build will use spdt ceramic vac relays, one relay per ant port. Then arranged in a microstrip configuration, so the main buss is always 50 ohms. And any ant port that is not in use, will have it's center conductor grounded.  Array solutions does this on it's remote ant switches, but they used DPDT mech relays, (contacts in parallel)... with red micarta insulation. Local electrician / ham buddy across town read me the riot act about using red micarta outdoors....since it can absorb moisture. 

I have pretty well given up on mech relays.  Vac relays are expensive, but at least you don't have to worry about moisture ingress.

[KL7CW]

Yes, sealed vacuum relays are a good option. Not always exepensive if you use surplus.  I have perhaps a dozen in use outside.  I got them from MFJ for less than $20 each I believe.  They were Kilovac I believe, and were labeled and advertised wrong, never could get MFJ to correct the error.  They were advertised as 12 volt 500 ohm coils.  They have 93 ohm coils which works out just right for driving with 6 volts.  I tested them on the far end of a dipole as an insulator with a length of wire following.  I think I ran 100 watts, so the voltage across the open contacts must have been thousands of volts.  So they work fine for a few remote matching networks, etc. at 100 watts. Comercially, we frequently use vacuum relays for various reasons.
           Do your own evaluation of the MFJ relays, since I have no idea of the real specs. and have been retired for 23 years and do not have test equipment for evaluation.  Dry nitrogen is often used.  Also you can get big bags of desicant from Amazon I believe for a few dollars.   Rick  KL7CW

[VE7RF]

Yes, sealed vacuum relays are a good option. Not always exepensive if you use surplus.  I have perhaps a dozen in use outside.  I got them from MFJ for less than $20 each I believe.  They were Kilovac I believe, and were labeled and advertised wrong, never could get MFJ to correct the error.  They were advertised as 12 volt 500 ohm coils.  They have 93 ohm coils which works out just right for driving with 6 volts.  I tested them on the far end of a dipole as an insulator with a length of wire following.  I think I ran 100 watts, so the voltage across the open contacts must have been thousands of volts.  So they work fine for a few remote matching networks, etc. at 100 watts. Comercially, we frequently use vacuum relays for various reasons.
           Do your own evaluation of the MFJ relays, since I have no idea of the real specs. and have been retired for 23 years and do not have test equipment for evaluation.  Dry nitrogen is often used.  Also you can get big bags of desicant from Amazon I believe for a few dollars.   Rick  KL7CW

I bought a  dozen of those same  kilovac DPST-NO  vac relays from MFJ last year. And yes, nine all measured 100 ohms dead on..and not the 500 ohms in their catalog.   I had to use my fluke dvm to tell they actually operated.  They are beyond dead quiet, totally silent.   They were listed as 12 vdc.    So used my 0-30 vdc @ 3 amp small lab supply to test a few of em.  The pickup vdc was exactly 4.5 vdc.    The drop out vdc was exactly 3.25 vdc.   They say to operate any vac relay coil at least 20% higher than it's pickup vdc.

They are stupid fast, and then some. Inside, they actually consist of TWO COM contacts. One moves down, while the other moves up..then they smack each other.  Noticed there is also an extra in / out wire lead, that has continuity all the time.  Apparently it's  either a metallic shield, so if several relays were mounted side by side, in a row, and say the middle one operated, the magnetic field generated would not screw up the coil on either side of it.   A 2nd function is to bond the shield of say RG-400 going in / out of the relay.  Apparently the relay contacts + this shield form a 50 ohm  Z inside the relay itself..and the relay just opens/ closes the center conductor.

The rated em at 5 amps @ 30 mhz, per contact, so in parallel, on paper they should handle 10 amps @ 30 mhz = 5 kw.

At 12 vdc, the coil draws 1.44 watts.

Funny thing is, that relay in the mfj catalog is no where to be seen in the KILOVAC website, nor in my high gloss KILOVAC
 catalog.   I found 3 x similar relays, that look the same in the KILOVAC catalog, but they are all SPST-NO types....and NOT the DPST-NO version that MFJ sells.   It's a bargain for $20.00   I would like to know where exactly MFJ / Ameritron used that relay...what piece of gear was it used in ?  I can't see it being used for any TR setup, since it's only a DPST-NO  and not a SPDT, or DPDT type.

Nobody seemed to know anything about it, or whether it could be used outdoors.   Moisture could get inside the hollow assy, upon close inspection. I got em to experiment with. One experiment, I used 2 of em to pad each air variable on a manually tuned, PI tuned input for a big amp.  (one kilovac relay with contacts in parallelel per  air variable.   Each cap is padded with 4 x 500 pf HT-50 caps.   (wired both coils in series, and applied 20-24 vdc)

Another experiment is to shunt portions of a hb strap coil on my 40m yagi..to extend the BW.  It works, but they are long things. Later switched to gigavac G2 flange types, since they mount vertical.  This is in the center of each element, so the Voltage is minimal, but the current is a bunch.

For the price, it's dirt cheap.   Did you mount urs in an enclosure     How did u manage to feed  6 vdc to each coil..and keep RF out of the 6 vdc wiring ??

[KL7CW]

My MFJ relays are mounted in an enclosure.  I bypassed each coil, I believe, with something like a 0.001 MFD capacitor.  No issues with 100 watts on 80 and 160 meters where I use them.  Run them all with 6 volts.  I do not think they would be easy to use in a Rat Pack switch, my frame relays work fine, but my Rat Pack is located inside a building.  I have no idea if these MFJ relays would work with over 100 watts since even at that power level voltages may reach thousands of volts in some network configurations, where a more traditional vacuum relay (expensive) may be indicated.
             Good Luck   KL7CW

[VE7RF]

My MFJ relays are mounted in an enclosure.  I bypassed each coil, I believe, with something like a 0.001 MFD capacitor.  No issues with 100 watts on 80 and 160 meters where I use them.  Run them all with 6 volts.  I do not think they would be easy to use in a Rat Pack switch, my frame relays work fine, but my Rat Pack is located inside a building.  I have no idea if these MFJ relays would work with over 100 watts since even at that power level voltages may reach thousands of volts in some network configurations, where a more traditional vacuum relay (expensive) may be indicated.
             Good Luck   KL7CW

I have never tried using any version of a vac relay out towards the ends of an ant. The peak V would be beyond wicked..and 41% higher than rms. 

Eventually, I will hi-pot test those kilovac vac relay's sold by mfj..and see exactly what they hi-pot test to.  Used at a 20-50 ohm feedpoint, they should be a non issue, since the peak V is minimal.  The idea here was, a small loop could be formed at the top of a tower, say for a 1/4 wave sloper for 160m.  And loop shorted with the vac relay. That would provide for 2 x segments, and extend the BW on such an ant.  With 2 x vac relays used, 4 x segments would be obtained.  Relay #1 wired to shunt out the 1st 3rd of the loop.  Relay #2 used to shunt out the remaining 2/3rds of the loop.

IE:  0/3, 1/3, 2/3, 3/3 could be obtained, by using various combinations of operating/ not operating the 2 x vac relays. Since they are DPST types, contacts wired in parallel, would handle loads of current on the lower bands.  On paper, that would easily cover a huge / most of the 160m band.

[KL7CW]

To VE7RF
  I also would not use one of these relays at the end of an antenna segment as an insulator, I just did this one time as a very rough test to see if it could handle significant voltage.  My relays are used in low Z places, and in networks where the voltages are high but not like at the end of a dipole.  I also use them to switch in the horizontal wire on my 160 meter inverted L, but again I do this to avoid having the wire connected all the time, because it runs just below my HF YAGI.  Actually I use about 6 of these relays to break up the wire into shorter lengths, and multiplex the 6 volts on the wire along with the RF.  A simple circuit e mail me at my ARRL e mail, if you want more info.  Will try to get back to you if possible, but me and my wife are struggling with health problems so may take awhile.  Works fine for years with 100 watts.  Your scheme looks OK to me, and I always like the idea of shunting out an unwanted loop section rather than using a dpdt as a switch.  You MIGHT be able to multiplex a control voltage on the loop along with RF like I did.  Possibly you could use + 6 V,  - 6V and possibly an AC voltage to get 3 different activations, again just an idea.  A decade or more a QST article showed a dipole with relay connected instead of traps at several locations.  I believe the author used pulses to control which relays were activated, he even sold a commercial version for a few years.  The dc pulses were multiplex right on the RF carrying antenna. This scheme of his is good, and probably worked fine, but was probably too complex, and heavy, and possibly expensive to really catch on.
             These are just my rambling thoughts, not designs.  No claim that they would work with say a KW.
     Have fun with your experiments, and let us know how things worked out for you.     Rick KL7CW  Palmer, Alaska