I recently purchased a variable capacitor to use with a homemade loop antenna for AM reception. https://www.ebay.com/itm/295176150101epid=1585666744&hash=item44b9de9c55:g:snYAAOSw6FFfjt-n&amdata=enc%3AAQAHAAAA0E5kda74mb7%2FK5xz63w7rZ4SEc2Y4bafgHDo78vNnzyALrdzuqXMtTOsPetvFSpQvJIKqaB4%2BRxLcHCn7O37%2FSQxFxrJZaeNM0BOVrTDzF1Bh64rh0XugBDtnsr99vQwZPmAiNw93F9%2FUrTysVilzHnfExWRypXoUK%2BFYBQtOXyJB6zPGNcTs5gZ2RwTk8jyeJ3ULLhMQU6J6ptE6MkRtAwRqkaGmddpD5og0BAwrfX5dmXsKXhqRxtcZxaUpT9Go7%2By2MZ0VvpALtX8ornz2Ls%3D%7Ctkp%3ABk9SR-Sy85_aYA I thought the one I purchased had two lugs to connect, but it only has one. Does anyone know where (and how) to attach the other end? Most of the pictures I've seen on the internet don't show this particular connection clearly.
connecting a variable capacitor with only one lug to an AM loop antenna
- Thread starter st25r
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Connect to the one on the side and either terminal on the back.
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Thank you for the response, WA0CBW! A question though... How would you attach it? It looks like I can wrap it through the center slit and then around the pole on the back or use an alligator clip to attach it.
You would normally solder them.
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prcguy
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If you look at most any variable plate capacitor, one connection will go to the rotating plates and the other connection goes to the fixed plates. Some may be confusing but if there is a lug attached to the tuning shaft that will make contact with the rotating plates. The fixed plates sometimes have a direct connection or you attach to the metal frame of the capacitor which eventually connects to the fixed plates.
How are you going to use the cap? To cover the entire AM BCB you need a good 350pf of variable capacitance to resonate the coil on a ferrite loop. A 5 to 100pf cap will only cover a small portion of the AM BCB.
Here are some good videos on making a great ferrite loop antenna and finding the resonant frequency of a loop and other related info.
How are you going to use the cap? To cover the entire AM BCB you need a good 350pf of variable capacitance to resonate the coil on a ferrite loop. A 5 to 100pf cap will only cover a small portion of the AM BCB.
Here are some good videos on making a great ferrite loop antenna and finding the resonant frequency of a loop and other related info.
prcguy
Member
I use that same eBay 365pf variable cap on my home made ferrite antenna, its a good capacitor for resonating an AM BCB loop. If you look at the second video in my links, at one point the guy is measuring the inductance of some ferrite antennas on an LCR meter. For AM BCB use the loop or coil inductance needs to be in the 249 to 250 microhenry (uH) range for a 365pf variable cap to cover about 530 to 1600KHz range.
If you made a random size loop and don't know the inductance you will have to either measure the inductance and change the length of wire in the loop or connect it to a receiver and map out where the loop peaks in frequency using the 365pf variable cap. It should peak near 530-540KHz at maximum capacitance and at or above 1600KHz at minimum capacitance. If you have an SDR receiver with spectral display the display will show the peak resonant point as you tune around and you can shorten or lengthen the wire to hit the target range of 530KHz with 365pf of capacitance across or in parallel with the loop coil.
If you made a random size loop and don't know the inductance you will have to either measure the inductance and change the length of wire in the loop or connect it to a receiver and map out where the loop peaks in frequency using the 365pf variable cap. It should peak near 530-540KHz at maximum capacitance and at or above 1600KHz at minimum capacitance. If you have an SDR receiver with spectral display the display will show the peak resonant point as you tune around and you can shorten or lengthen the wire to hit the target range of 530KHz with 365pf of capacitance across or in parallel with the loop coil.
Thank you again for the response, prcguy. I have terrible internet service out in the sticks. 144p video quality--barely--works, besides the fact that it is too blurry to see any detail. I do not own any an oscilloscope or an LCR meter. The radio I have it reads: tune, when the receiver thinks it's tuned in.
I was able to gather some things from the end of his part 2 video as well as some questions:
10-365 pf variable tuning capacitor is needed
It's put together with 1/2" cpvc pipe and fittings
1/2" cpvc slip cap fitting -is this where he winds the outer visible coil of 4-5 turns?
Would the two wires from this coil then go to the antenna jack?
45 turns of #24 wire around a ferrite rod, yet he says that he uses two 10X200mm non permeability 400 rods on the powerpoint. Does he somehow glue the rods together and place the coil onto the glued rod?
Does anyone know if he has the powerpoint or pdf that can answer these questions?
It looks like a great design, but maybe I missed the part in the video where he gives an explanation. Thank you again for your help.
prcguy
Member
The ferrite rod project starts with two very specific size ferrite rods from Russia or Ukraine and available on eBay. The rods are not glued and sit end to end inside the PVC tube wrapped in some thin foam sheet to avoid breakage as they are somewhat fragile. The outside of the PVC tube gets a specific amount of turns which I don't have at the moment but can look on the antenna I made. With the right amount of turns the inductance will land in a good range to resonate with the capacitor across the entire AM BCB range and the turns covers most of the PVC tube.
The first layer of turns put on the PVC pipe will go right to the variable capacitor via the wires out each end and the capacitor will be in parallel with the coil. Then you wind another coil centered over the first and about 4 turns which is the pickup loop. That coil will feed some coax to the input of your receiver if it has an external antenna connection. For AM receivers with a built in antenna you can leave out the pickup coil and just put the ferrite rod and variable capacitor next to the radio and peak the cap for best reception, it will really increase signals.
Tomorrow I can take pictures of my ferrite rod project which is basically the same as in the videos.
The first layer of turns put on the PVC pipe will go right to the variable capacitor via the wires out each end and the capacitor will be in parallel with the coil. Then you wind another coil centered over the first and about 4 turns which is the pickup loop. That coil will feed some coax to the input of your receiver if it has an external antenna connection. For AM receivers with a built in antenna you can leave out the pickup coil and just put the ferrite rod and variable capacitor next to the radio and peak the cap for best reception, it will really increase signals.
Tomorrow I can take pictures of my ferrite rod project which is basically the same as in the videos.
prcguy
Member
Here are pics of my ferrite rod ant. Actually two rods inside the PVC pipe. You can see the amount of primary windings and the connection to the variable cap plus the secondary pickup windings connected to a BNC connector.
I used multistrand Litz wire on this project. The rod will rotate and also tilts. I also added a low noise VLF/HF preamp and this antenna rocks for weak signal and it nulls really well.
I used multistrand Litz wire on this project. The rod will rotate and also tilts. I also added a low noise VLF/HF preamp and this antenna rocks for weak signal and it nulls really well.
prcguy
Member
You can certainly wind the turns right around the ferrite rod but this project used two rods and needed an enclosure to keep them together.
That makes sense. In a previous post you mentioned that the rods do not touch- they sit end to end. Does that mean that where the coil sits around the pvc pipe there is no rod? Or did you design it so that the end caps cause the rods inside the pvc pipe to almost touch? Thank you again for your help. As of just using the inner AM coil on my radio, I can barely pick up a station that is 30 miles away. I'm hoping there are some other stations in the area that will come in better.
prcguy
Member
The two rods and held tight up against each other inside the PVC pipe. I may have put a little foam rubber in each pipe cap to hold tension on the rods.
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