Ten-Tec Scout 555 60m Band Module Build: Final Filter Tuning & Field Testing [Part 3]

This is Part 3 of my Ten-Tec Scout 555 60-meter band module series. Read Part 1 and Part 2 for the complete build process.

Today I took the newly minted 60 meter band module for the Ten Tec Scout 555 out on it’s maiden voyage to a POTA activation. I made a contact in the shack with it before leaving on my short trip to Florida so I felt confident it was ready to use. Today we are discussing what happened and what is going on from there with the 60 meter band module project. (Spoiler Alert: It kinda wasn’t really ready yet…)

As you can see from the spot page report below, I was the only one on 60 meters this morning and it was roughly 9:45 (might have been 10 to be honest, I cant remember) local time before I got everything setup and running. This made 60 meters not a great choice to be honest for a daytime band. The 60 meter band is a great evening and really early morning band, but once the sun comes up these low bands tend to get really noisy. The band noise was quite low to my surprise today. I usually get a good bit of man made noise in this spot so I was pleasantly surprised when the noise floor was really low…or the band was closed. Who knows at this point?… I am starting to lean towards the band being closed as I couldn’t hear the FT8 crowd either, and those guys are ALWAYS on the band if it is open at all.

Undaunted by this and the lack of any kind of signal on the band, I setup and started calling CQ…and called …and called… then I finally got a station in North Carolina ( WA4CHJ - thanks for answering me, I really appreciate it. ) and with that I had a call in the log on 60 meters with a Ten Tec Scout 555!!! I can’t be certain this has been done by someone else, but as far as I know, I am the first to make that happen! After calling CQ for about 7 more minutes with no answers, I noticed that the ALC light was not coming on when I would key the radio and it was showing about 20 watts forward power on the built in meter. I checked the SWR and it was fine so it had to be in the module. I tried calling for a little longer and started getting an odd kind of “hashy” crackle on the CW sidetone and when it would make this sound the power would go up to the normal level and the ALC would come on…Upon this realization, I decided it would be better to sideline the module till I got back to the work bench next week instead of risk damage to the module or the rest of the radio. It also occurred to me that the RBN never heard me, not one time, while calling on this day so the band must have been closed…

You gotta admit though, that setup below is kinda sweet… Also the frequency is tuned off by the side tone (this is normal for the Scout 555) so it is actually on 5.3305 mhz in this photo. (I checked it with my Omni-VII before leaving home so I knew it was on frequency)

I setup a long wire today since my vertical will only tune to 40 meters with the home-brew load coil and I was a little strapped for time and just used an MFJ manual tuner instead. This allowed me to get a 65’ wire up in the air and a couple of radials and run with it. I was able to tune it well into the 60 meter band with the null covering the entirety of the band space so no tuner changes were needed as I moved around in the band.

SIDE QUEST:

This little segment will be about the rest of the activation for my readers that follow those as well.

Today was a great day…once I moved to 20 meters! Turns out 20 meters was alive and well today with only about 6 CW activators on the band. This gave me plenty of room to find a nice quiet frequency as well as lots of hunters were out today as well. I tuned up on 14.047 mhz and started calling CQ, I think it took two calls max to call in a extraordinary pile up for me! The stations were deep and strong! I swept aside my normal pleasantries for the most part and compacted the closing to what I felt was a minimum and the calls just kept coming in! I worked 49 calls in 41 minutes! That is a record for me! At this point I literally called CQ one last time to make sure there was no one else waiting and got no replies so I immediately called QRT and shut down the radio. I was actually out of time and had to get the rig packed up since I needed to pick up the wife from class. This had to be the fastest 49 calls in the history of WK4DS amateur radio in my totality of radio… haha.

MFJ was a company that some complained about (Surely you have heard them called More Fine Junk) but to be honest, everything I have ever bought that they made has worked exactly as described and was pretty reasonable in price too. I hope someone fills these shoes for the future hams coming into the hobby, this little tuner is amazing for what is in that tiny little housing. It tuned this long wire just fine and didn’t need huge capacitors or inductors to do it. Not to mention it was really economical too. Good kit is hard to find so if you plan to do POTA in the field, I recommend one of these in the box of stuff, it WILL bail you out one day. This tuner has bailed me out a couple of times now…

A throw line, a weight (that I made in the machine shop out of scrap stainless steel) and 65’ of wire made for a lot of fun today.

You can’t really tell it in the photos, but I did use my vertical antenna truck mount. I used it as the truck side anchor for the long wire and strung it up into the tree you saw earlier. This turned out to be really convenient I must say.

SIDE QUEST ENDED:

Back to the project at hand…

A week later and back in the shop at home with the band module on the work bench again and a Scout 555 in the shop now instead of the ARGO 556 to give me full power (40 watts) into the module (I pull the output power back to 40 watts to help protect the radio).

Now I can sort out the last of the details with the filters under full load. I am starting to think that the LO BP filter still needs some work as well as the signal level on the mixer output filter is REALLY high. I don’t remember the exact number but think of something like 700 or 800mV level instead of the 50mV that is supposed to be coming out. I tackle this problem first by building up the board like I had before so I could see the level coming out of the mixer filter. I had removed one of the impedance matching capacitors completely (750pf) without understanding what I had done and this was a big part of the problem with the level being so high. I did some simple math and came up with about 600pF instead of the 750pF that was supposed to be in the board since it was now tuned for 5.35 mhz instead of 3.55 mhz. I ended up using a 560pF cap and the level looked like the photo below on the base of Q16 in the radio. Remember this data is at this link if you need it as NA5N made these wonderful signal flow graphics.

Right on the money at 50mv! I will take that everyday! All the noise you see on the signal is generated in the radio as far as I could tell, all the band modules I tried today looked like this on the base of Q16…or I was picking up the noise from somewhere else, I really am not sure to be honest with you. The output from the collector looked fine though so I don’t know what is happening here. I know this is good now as the frequency in the radio is stable and doesn’t drift. Those NPO capacitors paid off! (NPO means “Negative-Positive 0 ppm/°C” or more plainly, these capacitors are stabilized so they don’t drift in value with a change in temperature) My circuit doesn’t look exactly like the original Ten Tec filter but it does work.

Below is what I ended up with for the filter circuit. I added the one capacitor that was not in the original design (the 43pf cap) and this did seem to help with the shape of the filter so I left it. I drew my filter flow direction backwards from the Ten Tec drawing but you can see the differences from the 80m filter I started with below. Also a couple points of interest here. In my 60m module (formerly an 80 meter band module), the output from the mixer chip is pin 5 on my board and not pin 4 that feeds into the filter network. If you look at the spec sheet, this is fine as both pins are output pins, but it was a curious mistake in the schematic I found while troubleshooting my module. Another curiosity to me is that the schematic shows L6 in parallel with C8 (5pf) in the center of the filter. Not one single band module uses L6… at all. The chart underneath the schematic shows a -0- symbol on each one of the modules for L6, to confirm this, I looked in three different modules and none of them have this inductor in them. It isn’t present on the 10 or 12 meter modules either as they have a different layout for their filters. This was a provision that later was deleted I suppose. Kinda neat to find things like this while doing a project. Makes you wonder why they provisioned for the inductor but never used it. The board has two through holes for the inductor as this is where I placed my 15pf cap (which made adding it really convenient.) So it was obviously designed into the system to start with… Maybe someone who was an engineer at Ten Tec back then will comment.

Excerpt from original Scout 555 owner’s manual.

With that out of the way I moved on to the output LP (Low Pass) filter that the 50 watt power amp flows through to get to the antenna.

The above photo is of a LP filter out of an unmodified 80 meter band module I used for comparison. If you will notice the roll-off is right smack dab in the middle of the 60 meter band on this particular module.

The photo below is of the 60 meter band module sweep that I am building out of an old 80 meter band module. If you will notice I have the nanoVNA set to 5.430 mhz on the marker, and it is hard to see, but the signal is at 0.05dB which is basically zero losses at the highest band position possible. This would imply that the filter would allow the 60 meter band through just fine, but it would not…

This is what the radio was sending to the dummy load after it passed through the LP filter module (above photo)… So to test this theory, I installed a different module (40 meters) and got what you see below… That is a little over 120 volts peak to peak on 40 meters. Yeah, you don’t change the output power of a Scout without a screw driver so the fact that the 60 meter band module I made is only letting a little over 30 volts peak to peak through it AND knowing that the 40 meter band module is passing over 120 volts peak to peak, tells me the 60 meter filter is choking off the energy and it is probably heating up the toroid inductors pretty good at the same time. I suspect that is what I was hearing the other day at the park when it was crackling after a while. I just hoped that I had not burned the wire on the inductors with this energy… If so I would have to rewind the inductors completely from scratch. Fortunately, I do have a roll of magnet wire I could do it with…

Into the final output LP filter I went (the one in the can) to see what I could do with it. The first photo shows the “can” the filter is shielded inside of to keep stray RF at bay.

The second photo shows what is inside of this can. This is also a photo of my completed filter with modifications to make it work on 60 meters. I found that this module had been tampered with once inside. Now to be fair, I did work on this module at one point to repair a broken inductor lead, but that was all. Now, I am getting much more serious while inside of the can…

I took another measurement with the nanoVNA and decided to remove the inductors and measure them with the LCR meter to see what it said they were. Turns out they were right on spec from the owners manual chart of 2.5uH each. At least that is what it looked like I read on the meter…haha. So I decide to remove an arbitrary number of wraps from each core (3 wraps to be more precise) and take another measurement to see what I had then. The meter showed them at 1.8 to maybe 1.9uH after pulling three wraps off. This put me right in the middle of 80 meters (2.5uH) and 40 meters (1.4uH) about perfectly. So I trimmed off the excess wire, scraped off the enamel so the solder would adhere to the copper and soldered them into the board.

Back to the nanoVNA for another round of measurements to find it still wasn’t where I wanted it to be. The frequency was still pretty low at the roll-off point. I then decided to look at the capacitors to see what they looked like. This is when I noticed that the band module had already been modified somewhat as the center cap was sitting at about 850pf already and not the 1500pf it was supposed to be. I also found that the two shunt capacitors on the ends were also different from the 80 meter module for some reason. I pulled these back to 470pf each and checked it again and now the band pass was in the 6 mhz area, this should be far enough away from the operational band to keep me from having problems so I put it all back together and then checked it into the dummy load.

Success! I am seeing over 120 volts peak to peak coming out of the radio! Woohoo! I couldn’t believe it! I had full power coming out on 60 meters finally! This was a real special moment for me to be honest with you. After this, I reassembled the shielding on the filter network and cleaned up the solder flux and put the module back together.

With all that done, all that is left is to set it up with an antenna and make some contacts with it…

Yeah…about that… There seems to be a major solar storm coming in and has been since the previous day. This is a big deal as you can see from the report. It has shut down radio for most operations. I did call CQ for a while and at one point I heard WY7EE calling CQ but he couldn't hear me. Figures. I did turn up on the RBN so the signal was getting out to some degree in the evening. That was kinda awesome to see as well. I know I have signal going out too as the wattmeter is showing 40 watts forward power. (Remember I de-tune my Scouts to pull some load off the finals since they are getting old and I don’t relish the though of having to replace them for a 10 watt boost in power output) 40 watts will do just as well as 50 from what I have seen in the past… anyway.

The next day we had the storm to start fading out a little and I loaded up the webSDR on my computer and listened for my radio on the Northern Utah listening post. Once the time was late enough, I started hearing my signal on the webSDR! I recorded it and posted it to my YouTube channel as a short if you want to go listen to what I could hear. This is the link.

Link to video about 60 meter signal

Like I said, I am going to revisit the band pass filter for the IF again when I get back into town. I think that can be improved a lot. (my current design is too broad banded in the pass band to make me happy, I want to clean that up some more.) I will write that up when I get the chance to work on it—read Part 4 for the IF filter redesign. Thanks for following along on this little adventure and I hope to hear you on the air at some point. Maybe you will work me on 60 meters with my Scout…maybe…

73 and get out there!

Ready for the final installment? Let’s read part 4 in this series now!

WK4DS

David