Even though I have yet to participate in any type of Radio Direction Finding (RDF) event, I find myself buying and building stuff for it. This time I decided to build an offset (active) attenuator as I think it’s a must need for RDF. When I was testing out my 3EL tape measure Yagi, I placed a transmitter on my property and tried to find it with a Yagi and found that it was near impossible to pinpoint the source as my radio was showing full scale and dead full quieting no matter where I went.
Since I’ve been reading a lot about fox hunting, I knew I needed an attenuator. However there are different kinds of attenuators that you can make or buy commercially. I wasn’t sure what to get at the time. I narrowed it down to the offset attenuator and the step attenuator. I went with the offset attenuator because it appears to be cheaper, easy to make and better than a step attenuator.
The attenuator that I went with was found on HomingIn.com’s Website. The article was writen by Joel Moell (K0OV) and explained in detail about the attenuator. What the offset attenuator does is “Offset” the received signal by 4MHz using a diode, oscillator and some other passive components. You are now listening to the signal away from it’s transmitting frequency. Your antenna and radio is no longer being overloaded and you’ll be able to get even closer to the signal.
It appears to be quite easy to build, even for me! So I went with it. The parts that are listen in the article are a little outdated
Here is an updated list of parts that I purchased. I usually use Mouser for components but I wasn’t satisfied with their shipping to the North East so I used Digi-Key with better results
|1X||CAP CER 470PF 2KV 10% RADIAL||$0.23 ea||1286PH-ND||Digi-Key|
|2X||CAP CER 4700PF 50V 10% RADIAL||$0.30 ea||BC2683CT-ND||Digi-Key|
|2X||RES 2.2K OHM 1/4W 5% CARBON FILM||$0.10 ea||2.2KQBK-ND||Digi-Key|
|1X||RES 4.7K OHM 1/4W 5% CARBON FILM||$0.10 ea||4.7KQBK-ND||Digi-Key|
|1X||DIODE SMALL SIG 100V 200MA DO35||$0.10 ea||1N4148TACT-ND||Digi-Key|
|1X||OSC 4.0000 MHZ FULL SIZE||$2.49 ea||CTX774-ND||Digi-Key|
|1X||BNC FRONT MT RECEPT SHORT||$4.67 ea||ARF1064-ND||Digi-Key|
|1X||5K Audio Tape Pot||$3.49 ea||#271-1720||Radio Shack/In-Store|
|1X||Perf Board/PC-Board||$2.49 ea||Radio Shack / Instore|
|1X||SPST Swith||$2.49 ea||Radio Shack / Instore|
Total project cost: Approx $8.00-$18 USD
Making Sure Everything Works
Before putting it on any type of board I wanted to make sure that It works. I never really messed around with making electronic devices from a pile of parts. I put the entire project onto a breadboard following the schematic as close as possible
Here it is being tested out on the breadboard It went together pretty easy. I used a voltage meter to make sure the correct voltage is coming out of the LM7805 regulator. I was seeing around 5V
Here is a video of it in action
Now that I know it works, it’s time to transfer the design to a more permanent home. I wanted to compact it as short as possible to get it to fit into a small PVC box. Since I had a PVC box I wanted the board to go into, I measured a piece of perf board and cut it up
After cutting the board, I laid out all the components and attached all the wiring I could from underneath the board
Here its with most of the stuff attached.
Here is the Top view of the board. I had to use some jumpers (red and green wires) to get some of the components to make contact.
The black wires you see leading away from the board are for power and the adjustable resistor. I tried to test it out at this point to make sure it works before adding the coax and other things but It turned out not to be worth doing. But I did check the circuit wiring a couple times to make sure.
Getting it jammed into the small box was going to be difficult. I knew right away that I wouldn’t be able to fit the 9V battery and the circuit board into the same compartment without using a larger box.
Here is the PVC junction box with the circuit board, switch, POT and cabled jammed into it. I had to have shave some of the flange off on the cover as the Pot is almost the same size as the Inside dimension of the box.
To solve the battery issue, I fabricated a small aluminum box that can hold a 9V battery. I drilled a small hole in the side of the PVC case to route the power cable through. In the above picture you can also see the on/off switch and adjustable pot. I mounted the switch sideways to avoid any accidental switching even though it’s still possible.
Here is the fully assembled antenna. The PVC junction box is also used to mount the grip handle. This way most of the weight is sitting on top of my hand instead of out on the boom. I also didn’t want to put any kind of electronics/metal between the reflector and driven element. Not sure if it would make a difference but I think it’s better off this way
I learned a lot while making this attenuator. The circuit was simple enough to where I can understand what is going on.
If I were to build another one, I would make some changes to make it even better. The big problem is that the coax runs from the driven element straight into the attenuator from inside the PVC. This doesn’t allow me to swap out antennas. What I would do is put a BNC connector sticking out of the PVC box and have the coax come out the boom to make the connection. I could just make an attenuator that is seperate from the antenna but that is just another bulky piece of equipment to carry around. I wouldn’t want to attach it directly to the radio because I think it would put strain on the connector that is in the radio.
You also can’t TX using this antenna. If you do, you can kiss the diode and possibly other parts goodbye. I would try to install some kind of switch that would allow me to TX but I’ll just carry an extra antenna or extra radio for now.
Hopefully it will see a lot of use.
Thanks for reading!
Jeffrey Bail (NT1K)
Now that my station has grown, I have quite a bit of equipment that requires 12-14Vdc of power. In the past couple of years I decided to start using Anderson Power Poles. I decided to use them as it’s starting to be the standard of some organizations and It’s easy. My only complaint that I would have is that sometimes the connectors can loosen up and doesn’t require much force for them to come apart.
At this point I have a very minimal setup that needs to be expanded. I have a pigtail off the power supply and set of power poles on each device. If I wanted to use one device, I would have to disconnect power from one device and put it on another.
The obvious solution to my problem is the use a distribution panel. There are some commercially made panels that use Anderson power poles but being the cheap ham that I am, I figured I can find a cheaper way.
While at a local hamfest this past weekend, One of the vendors had a bunch of products that use the Anderson Power pole. Two of those products has caught my interest. One of the was the “EZ-Gate” by ham source and the other was distribution block by Quiksilver. The EZ-Gate is similar to the PWR-Gate by West Mountain Radio but doesn’t have LEDs or Fuses. The EZ-gate is half the cost of the PWR gate and this would allow my station to instantly switch to battery backup during events like field day or when the power goes out in my house. The power distribution block was just a simple 4-way connection using power poles and priced at $20. I thought the price was fair but I thought would be cheaper and fun to make my own at home, For the price of one block, I decided to get twenty pairs of power pole connectors.
Having no clue how the little distribution blocks were made, I thought of way that I think it was done with the commercially available ones. I used 12ga soild copper wire to connect everything together.
Here is a photo of what I started with and the final product.
I cut 4 wires about 1.5″ long and placed the connectors on each end and did a quick assembly to check the gap between the sets. I wanted the gap to be short as possible so the entire block would remain rigid. I also cut and bent two additional wires to act as a “link” to the top and bottom sets.
Here is one of the wires that I crimped the ends on. After crimping I soldered each end to make sure of a good connection. Please note that the connectors on each wire are opposite angles from the other side. At this point I installed the wire and marked the location where the link will go with a sharpie.
Two of the four wires, I soldered one “link” favoring one side of the wire.
Here it is halfway assembled. you will notice the link on the positive side very close to the connector. When the other side will be installed, the other link will be close to the negative block on the opposite side.
Before connecting the other side, I used a pair of pliers and curved the links around the top stack of the link.
After completely soldering the links and installing the other end, I wrapped the positive side in plastic. If I were to do this again, I would solder, install heat shrink tubing both leads and then install the other set of connectors.
For what I would have paid for ONE commercially produced block, I’ve made two blocks and had and also have an extra set to make a patch cable or pigtails/adapters.
It’s no rig runner but it works and does what I need it to do.
Thanks for reading!
After seeing a lot of articles written about making a three element Yagi using PVC and a tape measure, I was interested but not excited about it. That was until I made a QSO with K1MAZ (Nick) while he was doing a SOTA Activation. I decided to try to make contact with Nick on VHF as it was spotted on the SOTA website. Nick was on top of Burley Hill in Union CT which is about 30mi from my QTH. He tried using his stock antenna on his Yaesu Handheld but it’s just a little too far out of range. I knew someone was trying to get in but there was no copy. A couple of minutes later I hear him again, but it sounded like he was in front of my house. He was S9+ and very clear audio. After meeting up with him I asked what antenna he used and he said that he was using his Tape Measure Yagi. I was somewhat amazed that it worked that well.
Now I want to make this antenna. It appears to be real easy to make and requires only hand tools. I ended going with a mixture of three designs
The first design I went with was from WB2HOL which appears to the origin of this particular antenna. It’s designed to be a RDF (Radio Direction Finding) antenna. It could also be used in portable operations like SOTA or Field Day. I obtained all the dimensions needed from his website.
I got the boom design from the Camden County Radio Society’s website which is slightly different from WB2HOL. It replaced the tee used by the director with another cross tee and added a 5″ stub. I have no particular reason why I went with this book design. I just liked it and it avoids adding a different part even though it’s no big deal.
Finally I got the choke from an article published in QST Magazine (May 2007)
Is the choke/balun needed? I’m not experienced enough to give you a yes or no answer. I decided to use it because it wasn’t going to cost me anything to do it. If it didn’t work our or was causing an issue then I can just simply un-wind it.
I am not going to go into detail about making the beam as it’s already done for you in the those articles that I linked to above.
However I will provide a detailed blueprint that is a little better than what I’ve seen out there.
Please use all safety cautions while working with tools and parts!
I tried as best as possible to get the exact dimensions of the PVC caps and cross tees but I found that the dimensions vary between manufacturers. That will explain the 0.060″ (1.5mm) differnce in element spacing as noted on the print.
Along with the instructions on the blueprint, I would like to share some of my personal experiences when it comes to building and using the antenna.
Working with PVC Tubing
I didn’t have a PVC cutter as I rarely do PVC work. I also didn’t have a vice or clamp setup to use a regular saw or sawzall with. I ended up using a tubing cutter that is normally used on copper tubing for plumbing. It worked but it wasn’t pretty. It pushed the PVC to form a flange or lip around the entire diameter of the tube. I had to use a sander to remove the burr/lip.
PVC Cut into lengths
I also decided NOT to use PVC primer and cement. The parts fit together so tight that I didn’t even bother using it.
Antenna Boom Dry Fit – PVC was so tight fitting that I didn’t bother using glue
Tape Measure Sharpness
The tape measure is somewhat sharp along the long edge. It’s not razor sharp but it’s sharp. Cutting the tape measure creates a real sharp edge. You can combat this by either wrapping the exposed edge with electrical tape or cutting a chamfer (corner) or both. I’m going to use a product call “Plasti-Dip) and coat the tips of each element with it.
Hopefully you will be careful running around with the beam. Doing this will make things just a tad bit safer.
I’d would either dismantle or cut out the bad sections of tape. If you already have a 1″ wide (or bigger) tape measure, I’d suggest buying a new one and cut apart your old one. I’ve notice coating usually wears out within the first couple of feet. My suggestion would be to start cutting the tape up from the oppisiet end.
Soldering the Hairpin and Coax
There is also an issue when it comes to soldering the tape measure. If you have normal flux core solder, you might have a hard time soldering the wires to the tape measure to where it won’t stick. I ended up using a liquid flux that is commonly used in the plumbing/welding industry. It’s an acidic flux that works great.
After grinding away the paint/coating on the tape measure, I put just a teensy drop of flux on the exposed metal of the driven elements. After soldering the hairpin match and coax using a 100W iron, I took it over to the sink and washed off any left over residue that was still on the tape. I’ve been told and I’ve read that using this type of flux is pretty corrosive and will eat away at the metal it was applied to causing a bad connect. So please be careful. After a week of playing around with it, I have not noticed anything.
Running the cable through the boom.
You will notice that I drilled some holes extra holes. I want to run the coax through the center of the boom, have it come out to start the coil and back through. I did that so the cable couldn’t drag across or get snagged in the reflector and to provide a little more security with the coil. It’s not a big deal but I found it to be cleaner than having it zip-tied or taped to the boom.
Cable Through Boom
You can build this antenna for under $20. Since I work in trade where a lot of people accidentally cut off or destroy their tape measures, I have quite the collection of tape measures.
8FT of 1/2″ Schedual 40 PVC Pipe - $3 (Home Depot)
3 PVC Cross Tees 1/2″ – $1.50 Ea ($4.50) (Home Depot)
2 PVC Caps 1/2″ – $0.40 Ea ($0.80) (Home Depot)
6 SS Hose Clamps – $1 Ea ($6.00) (Home Depot)
1 Tape Measure – $3 (Harbor Freight)
Grand Total – Approx $17
If you already have a 1″ wide or bigger tape measure in your tool box, I’d suggest on purchasing a decent tape measure and use your old one for this project. When it comes to using used tape measures, I would make my cuts starting from the other end of the tape. Most used tapes have lots of wear and tear on the first 12″.
Also don’t cheap out and get regular steel and electrical grade PVC conduit. The clamps will rust and the electrical PVC has a thinner wall and will easily flex. It may not happen right away but time will take it’s toll. I know it’s a cheap antenna but it would be more cost effective in the long run.
Well Did it work? I would say so, I don’t have an analyzer to tell you for sure. I hooked up the antenna to a SWR meter (bridge) and was seeing 1.2-1.5 on the meter. I went out in the back yard of my house and I’m sure my neighbors think that I’m training to be a JEDI fighter or something with the way I was waving the antenna around. I ended up hitting a couple of repeaters that I couldn’t normally hit with the stock antenna
Here is a video I made really quick to show it in action
Nothing exciting but it was fun.
Here is the complete setup. I gave myself enough slack on the coax incase I decided to mount the yagi on a tripod.
Overall it was a really fun build. It didn’t require any type of heavy equipment or tedious work. I have a feeling that running around the woods with a tape measure will end up with crimped or broken tape measure. However it would be much better that running around with 1/4″ (6.35mm) aluminum rod. Replacing the director and reflector would be easy as cutting the tape measure. So fart so good!
Thanks for reading,
This is the 3rd and update to my HeathKit SB-200 Amplifier Project.
The amp has been running fine since I’ve got it going. I had a resistor pop in the parasitic suppressors and I think that the amp is running too hot in temperature for little time I use it. At this point I am placing the blame on the two muffin fans that are currently “Cooling” the tubes. I am thinking that the fans are not providing enough air to cool the tubes fast enough. When I was replacing the parasitic suppressors, I performed some modifications (see update #1) and ordered a new fan from Harbach Electronics to see if it would make a difference.
I also held out on performing a couple more modifications because I had to fabricate some parts to encase the glitch resistor so if it were to pop, most of the resistor mess would be contained. The fan was placed on back order so It gave me time mark up and cut the lexon glass to sandwich the resistor with.
The fan kit does come with installation instructions which at first were a little difficult for me to understand. This was due to the fact that the new fan is a modified replacement of the original fan that came from Heathkit and I had purchased the amp with PC type fans. There is pre-assembly you have to do to the fan before installing. It involves removing a couple of screws on the fan that stick out and replacing them with shortened screws. Then you have attach aluminum spacer blocks to the fan which the block also has holes spaced out to fit in the orignal pattern of the fan from Heathkit.
The installation is pretty simple and straightforward. The kit comes with new rubber grommets to absorb any minor vibration that the fan causes.
You can either cut the wires near the old fan and tie into them or what I did was un-solder the old wires and wire the new ones in place.
I initially wrote this article in early may. I wanted to do some other upgrades at the same time but the New England QSO party was really close so I decided just to do the fan. The install went easy and would like to thank those at Harbach for rushing out the part. I made sure the fan was balanced as much as possible and I was able to use the amp during the entire contest. It’s a tad bit louder than the PC Muffin type fans that were in there but you can actually feel more air being pushed with the replacement fan. Over the past months the amp has performed very well. I should find more screws to secure the hood and the sheet metal covering the tubes/rf deck as it tends to rattle during operation.
Well, after a month or so of operation with the SB-200, my first “oops” happened. I went to turn on the amplifier and I thought I had everything correct and when I went to TX I heard a loud “Pop” sound. Quickly shut off the amp and disconnected the power. Opened the case to find that one of the resistors and the parasitic suppressors popped. I knew something was going to happen because the resistors were turning black.
Since I had to fix the suppressors, I figured this was the time to do some other “Modifications” to the amp. When I first rebuilt the amp, I ordered all the parts to do almost all the mods that you see on KL7FM’s SB-200 Page. I figured since it’s opened up, this would be the time to do SOME of those mods listed on his site. Are these mods needed?.. Nope! If they were then I would assume that they would have been incorporated a long time ago. I just figured if it makes it run a fraction of a percent better, why not invest the extra couple of dollars.
First thing I did is replaced the Parasitic Suppressors and I also replaced the .001uF 1kV ceramic Disk cap with a .0025uF 10kV disk cap (as seen in orange in the picture above),
Apparently it allow less RF to leak back into the power supply on the lower bands. Cap was around $2.00US
In this photo I replaced the two 33ohm carbon resistors that I had with some higher wattage metal oxide resistors. I then replaced the 3300Ohm resistor with a high wattage metal oxide type as well. I also replaced the 2 200pF caps with 4 470pf 1kV. I guess by replacing the caps, there will be decrease the grid-to-ground reactance for better improvement on the lower bands.
In this photo I replaced the nylon protected wire for the input to the cathode and replaced it with a 10Ohm 3W resistor. I guess this will help dampen the VHF oscillations as well as help by prevent over driving the amplifier.
After hooking everything up, The amp turned on and sprung back to life. After messing around with it for a couple house, I haven’t really notice really any improvements. doesn’t mean nothing is happening which is WAY better than having it break on me. So it was a success.
Since the AMP has been operational, I’ve notice that it gets very hot with little use. My gut is telling me that the Pancake AC fans are not doing the job efficiently. The fins are quite small and most of the room is taken up by the motor in the center. I am seriously considering the purchase and installation of a replacement of the type of fan originally used in the SB200. The company that sells the fan kit want over $60 and I am still tossing it around in my head. So far I keep my eye on the temp and I’m using a bigger fan that sits on top of the case to exhaust the heat. |
When the time comes to install the new fan, I am also going to do more modifications that were on that website that have to do with protecting the power supply and the meter. I might even go as far as replacing the meter light with an LED that turns Red when I’m TX. I also might change the “REL Power Sense” POT with a Switched POT so I can put the AMP in standby mode. Hopefully after this, I will never have to go in that amp ever again!