WK4DS Amateur Radio Blog

David Saylors 2/7/26 David Saylors 2/7/26

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

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…

tentec scout band module low pass filter

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!

All four parts are here:

- Part 1: Initial Conversion and Filter Design

- Part 2: Crystal Selection and Mixer Circuits

- Part 3: Field Testing and Troubleshooting

- Part 4: IF Filter Redesign (this post)

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David

David Saylors 1/21/26 David Saylors 1/21/26

Building a 60m Band Module for Ten-Tec Scout 555: Crystal Selection & Filter Design [Part 2]

Well, if this is the first post of my blog you have found about the 60 meter band module, please Read Part 1 for the complete background on this project. or a lot of stuff is not going to make sense…haha.

The donor about to undergo surgery to become a 60 meter band module.

As you know from last week, I was able to get all the filters updated except the output bandpass filter for the mixer and changing the crystal, so let’s get into that today.

I figured the the mixer’s bandpass filter would be the same as the IF filter but turn’s out I was wrong here. I looked at the existing part values on the chart for 40 meters and 80 meters (remember that part about not having a formal education in this stuff?) and simply decided that the inductors were again too big and I needed them to have a slightly lower value instead. This is where things get engineery..is that actually a word? It should be. I started by simply using an online calculator to figure the values for this filter based on the chart from NA5N’s Website and my own simple math of a mixed product of 11.442 mhz. It falls right in the middle of the 80 and 40 meter LO frequencies on his chart. So now I needed a crystal…

Luckily I didn’t need matched sets like when making a crystal ladder filter so I was able to find 9.218 mhz crystals on Digikey for reasonable money. The calculated crystal frequency I came up with was 9.242 mhz to land at 5.300 mhz. This radio will absolutely transmit out of band and it is the responsibility of the user to stay in legal band space so I figured this would cover the entirity of the 60 meter band. The NA5N chart shows the PTO minimum frequency is 2.2 mhz so that is where I started my math.

2.200 mhz (PTO min.)+9.218 mhz (PTO XTAL)=11.418 mhz (LO) - 6.142 mhz (IF) = 5.276 mhz

The entirety of the 60 meter band is from 5.3305 mhz to 5.405 mhz so this will work perfectly fine.

All this math starts to make sense when you look at the chart at the bottom of this page. That is why I keep linking it…haha. So I build out the band pass filter and install the new crystal when it comes in and … nothing… Well, it did something actually. It would not lock onto the frequency at all, it would attempt occasionally, but most of the time it would just scroll numbers on the display of the radio. It obviously was not working. I was sure I had built the filter right… (turns out I was dead wrong…again…I am starting to see a pattern here…haha).

As I would soon find out, I built the filter for the 40 meter IF by accident. At this point I had a lot of numbers floating around in my head and scribbled on various pages laying around the bench and one was where I had done some of the math around the 40 meter circuit for some reason and I inadvertently used those numbers to make the inductors with. Couple this with a trip out of town for a week and you will see where I lost my train of thought. Once I returned from the trip I had just two days before leaving again to see what I could figure out.

Well, this is what I figured out.

What you see above is a frustration point to be honest. I studied the print long enough to realize I could bring the circuit to life if I had a signal generator and a power supply. To get this to work I soldered several small scrap clippings from component leads to the board in strategic places to be able to connect leads for various devices and you get what you see above. I immediately went down a rabbit hole on signal generators and ended up with a UNI-T UTG962E and it arrived THE DAY BEFORE WE LEFT ON OUR TRIP. I get it going and power up the circuit with the 10 VDC bus and then inject a 2.2 mhz signal from the brand spanking new signal generator into the line (simulating the PTO) to see what I would get at the output… well… nothing. I checked the crystal and I had a clean 9.218 mhz signal at about 700mV going into the mixer chip but my 2.2 mhz injected signal was 50mV (the signal level based solely on the output shown on the block diagram going into the receiver control board as the data sheet for the chip I found didn’t show a signal level threshold that I could find.). This was obviously too low and I started turning up the signal generator and nothing happened at first. I was at 700mV of signal level coming out of the generator and I was getting nothing at the output of my filter. So I start walking it back to the output of the generator. I didn’t have anything at the output of the mixer chip as it turned out, so I check the inputs to the chip on the chip directly and the PTO input was almost non-existent. Turns out that the output impedance of the signal generator and the input impedance of the low pass filter for the mixer chip on the board must be different as it was dropping the level pretty dramatically. (This is something else I have learned while doing this project, you have to observe the impedance between stages or it wont work. ) So what do I do to solve for this? (Remember again I have almost no formal education in this area of expertise) I simply put the scope on the output of the mixer IC itself and slowly start turning up the 2.3 mhz amplitude till Eureka! The mixer sprang to life and I had a product!

Note: I am using a different value here for the PTO reference signal because I didn’t notice that I had changed it till I got the mixer working. But it is fine as the PTO operates from 2.2 mhz up to about 2.7 mhz anyway. The key was getting the bottom of the mixed product below 11.425 mhz when the PTO is at minimum. This will allow tuning through the 60 meter band. But this is why the number in the photo below is 11.520 mhz and not 11.425 mhz.

Now that I have a signal coming out of the mixer IC, I need to see what it going to the receiver control board. You see on the signal path drawing from the NA5N site that he states it should be 50 mV or so there. Well I had nothing coming out of the band module at all. I start looking at the filter and this is when I figure out the filter is all wrong. Back to the drawing board again. I take the week long break and during this time away I dwell on what I had learned and spend even more time trying to learn how this bizarre filter works. It looks somewhat like a regular band pass filter but there are elements that don’t make sense to me. I spent a considerable amount of time studying this problem and decided to order some inductors and when I get back I could replace my home brew ones and see if I had done something wrong there.

Fast forward a week and I went home and had about 5 hours total to figure the whole thing out or it would wait yet another week… I start by replacing the two home brew inductors with two 2.2uH inductors from the variety kit I ordered. Still didn’t work, so there must be something wrong with the capacitors too. All of the caps at this time were class 2 capacitors so that would turn into a problem as they warmed up, but this thing was not working even when it was cold, so the values were wrong is all I could figure. The most logical thing was to strip them all out and start over. I had now gotten my hands on some NPO caps too, this allowed me to build out the filter completely with the correct rating capacitors thereby giving me the confidence that once it is working, it will hold value.

My first batch that I bought was a literal double handful of random NPO capacitors (and a few other ratings mixed in for fun) thrown into a box from eBay. I knew what I was getting so I also picked up some divider boxes to sort them when I got time. Now they are all sorted and I know where to find what when I need it. Of course, I don’t have every conceivable size to choose from but I do have a large assortment and can get by with most projects with what I have. Things like this are what I wished I had learned in trade school… I guess I should have chosen college instead…you know what they say about hindsight though...

The photo of the board above that shows all the leads connecting to temporary test points I soldered to the board has these capacitors on it. They are temporarily soldered on as I am experimenting with various values in different locations to see what will get me to where I need to go.

I tried to use the online calculators but this filter doesn’t fit into any of those models and all the outputs from those tools were not working for me. It looks like the coupling capacitors are also used to also limit the signal level from stage to stage as well. Correct me if I am wrong in this assumption, but tiny little 5 and 8 pF capacitors are not letting a lot of energy through them, even at HF frequencies and there are two in this filter circuit. I can only assume that they are also using these to match impedance as well or a larger value would couple the stages with more signal. Anyway, I was stumped and asking the internet for help is literally begging to be slandered and chastised for being stupid, so I didn’t even bother with that option. That only left experimentation and experimentation is what I did. I put all sorts of outlandish caps in this filter and found success doing it this way. It took me a few hours, not gonna lie, knowing how to calculate these sorts of things would have been immeasurably easier, but I was able to get the signal on the output trace of the band module and it had decent signal level too! Honestly, I am going to revisit the output signal level when I get back home (I may have already done it by the time this goes live on my site) and see if I can attenuate the level somewhat as it is higher than what the base of Q16 on the receiver control board shows in NA5N’s pictogram.

What you are seeing above is the output of one of my Argo 556 radios that I used as a test bed to check the signal levels and such to see what was going on with it. As you can see I simply connected to the output of the radio and looked at the signal going into a 50 ohm dummy load. I did the math (I know, I know… this has not been a great idea for me in this blog post… lol) and it comes out to about 1.8 watts and not 5 watts for this radio (I have not attempted to turn up the transmit power on this unit yet either so it might simply be turned down or something like that. Let me know if my math is wrong here, but 27 volts peak to peak and 50 ohms should give me a power level of 1.82 watts at the antenna connector?

Power= peak voltage (13.5volts) divided by the square root of 2 and then that is divided by resistance.

All that aside, I took the newly minted 60 meter band module up to the shack and setup a Scout 555 and connected it to my home antenna. Tuned the antenna up and started looking for a QSO. I promptly found one and had a short ragchew with VE3USP in Ontario despite some QSB along the way. It works perfectly too. I do have to dial up 600 hz to be on frequency as it is a Scout 555 after all, but that is not a problem!

So I am not completely finished with this module as of yet. I still want to look at that output filter from the mixer and tune it some more. It is close, but it is not right as the signal level is too high. I found I missed a couple of capacitors when I dismantled it to clean it that need to be NPO capacitors instead of what I currently have in place as well. I would also like to improve upon my terrible painting skills if I could figure out a way to do it…lol Seems acrylic craft paint might not be the best solution here…

Next week we get into what happened when I took it to a POTA park… hint: I brought it back home and got inside a little more to fine tune it…. I discuss this next week and show you what I came up with for the mixer output filter ultimately.

To read the other parts:

- Part 1: Initial Conversion and Filter Design

- Part 2: Crystal Selection and Mixer Circuits

- Part 3: Field Testing and Troubleshooting

- Part 4: IF Filter Redesign (this post)