You have heard me mention KG4WBI a few times in this blog. He literally has what seems to be a veritable museum of vintage ham gear.
Well in today’s episode of “what oddball, ancient but yet working piece of gear is he going to pull out today” he hands me an amplifier. It is the OUTCOM OPA-202 to be exact and it has a feature we are really interested in. It doesn’t have a keying input which means it is RF sensing only. This stands to reason too as it also takes 1-10watts of RF energy and turns it into almost 175 watts on the output. At least that is what the literature says.
Here is my current test setup for gear, I have a coax stubbed out to the shack bench plus the Astron has powerpoles on the front making for an easy temporary setup location.
Made in copious quantities at what appears to be the end of the last ice age, the OUTCOM OPA-202 was a ham radio amplifier that was designed for 40 meters to 10 meters. Now your going to say, David, I know that…it says that right on the front with the 7-30mhz. I think this was done to target both the CB genre as well as the amateur radio group but I dont know for sure. What is odd is the literature below shows that it is rated for 80 meters too. Who knows what the lowest band it will work on is… I do know it works on 20 meters and 17 meters though as I tested it on both of those bands with my Penntek TR-35 transceiver.
The next thing you will notice is the selection buttons are labeled only for voice modes. This is another marketing ploy to help sell these little power houses. The buttons are actually power output selectors and depending on the combination you can theoretically get up to 175 watts out of this thing. Seen below I have it set to “SSB” mode which turns out to be semi break-in keying and 80 watts out. There are 4 levels depending on how you set the “AM” and “SSB” switches, but it also limits the amount of energy/duty cycle depending on the mode. It actually lists CW in the modes and the output and such, hence I am not running it full tilt. It also has protections built in to keep the over zealous operator from working it to death with long winded conversations. This particular unit seems to produce full break in keying if you select “AM” and semi break in with “SSB” modes. Probably due to the style of transmission coming with each of those modes. AM will produce a carrier the whole time you have the radio keyed and SSB only when you talk. To smooth out the relay action in SSB they have added a 1000 microfarad capacitor and a 470 ohm resistor to the relay keying circuit to keep it closed in just a little longer when SSB is selected so the relay wont sound like a machine gun. Another switch right beside the power switch is the pre-amp switch (REC AMP) which turns on a receiver pre-amp for weak signal work and it actually performs really well. I used it quite a bit and liked in particularly well.
So Roger wants me to … as he puts it… play with it and see how it works. This is his way of giving me something new to write about. LOL Once done, his plan is to integrate this amp into a vintage Field Day kit. This would be a neat little addition to his early Argonaut 2 that he has since it is only 5 watts output at full power.
In the flyer above, the bands go all the way to 80 meters but the unit we have doesn’t list 80 so they must have updated the specs over time for some reason.
Back to the RF sensing part, the reason we want this is it simplifies setup at field day for us. If we want to use QRP power for our ops then we can but if the bands just aint cooperating then we can easily add some power and get things moving. Our goal has always been to see if we can get on the air with QRP first and most years we are successful but occasionally we are not. So this allows us that leeway to be able to add output power as needed easily and with literally any radio we connect to it. We like this design so much that we are going to hijack the RF sensing circuit and see if we can copy it for another little amplifier he has that doesn’t have current sensing. We think it should be a simple thing to build a little project box that goes between the radio and amp that has both coax ports, a 12v power cable and a simple keying cable coming out to connect to the keying input on the amplifier. We even considered using the little 4 pin Amphenol plug so it will look “official” when we build it…hi hi.
Things of note about this amplifier, it has no fan, so it is static cooling only with the enormous heat sink that is attached. Don’t forget you have this monster of a heat sink when you install it in your car too as it will be on the bottom and I am pretty sure it needs ALOT of air to be able to keep it cool enough at full power. Another thing is the meter on this unit is frosted over, but no worries as when you key the radio, a light comes on behind it and lights it up just enough to be able to read the milliamperes DC that are flowing…somewhere…lol. Actually, from what I gather, the meters in these amplifiers were terrible and replacement was pretty common so apparently someone replaced this one and didn’t switch out the backplane so the meter would read right. It is supposed to be some sort of SWR meter from what I can gather by reading the manual.
Lastly, someone has replaced the power cable with new wire…and left the bulkhead connector off so I will add one back if I can find one before returning it to Trey. At least it is fused on both the +13.8 as well as the ground lead. That is nice when the insulation breaks down at the sheet metal and decides to short one of the wire.
Anyway, all that said, his museum piece actually works as I made several CW contacts with it using my Penntek TR-35 QRP transceiver. The little radio has plenty of drive for the OUTCOM OPA-202 so I was easily able to get 80 watts without issue and this was plenty to work one ragchew QSO as well as several POTA contacts. The system looks a little messy on the bench but will quickly clean up now that I have proven it works. So until next time, 72…errrr…73
de WK4DS