Build an Active AM Broadcast Ferrite Antenna /w Phase Loop
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- Опубликовано: 18 янв 2019
- An active AM Broadcast antenna w/ ~32 dB of gain using 4 JFETs. The antenna uses 2 Ferrite rods w/ Litz wire in parallel to increase gain in addition to a 10" Phase Loop antenna that can be tuned separate to reduce noise and heterodyne whistle, etc. The Phase Antenna default position provides excellent performance, but can be shifted closer or away from the base to optimize performance. There's no direct connection to the receiver, just a Loopstick Antenna that transfers the signal via induction.
A simple modification is called out to allow the antenna to utilize a direct connection: • Active AM Broadcast Fe...
My as-built drawing: drive.google.com/file/d/1I-Dj...
Thanks for watching and subscribing to my channel on vintage radio repair.
PARTS LIST:
Capacitors:
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C1, C2 - 0.01 uF, ceramic-disc (optional)
C3 - C9, C11 - 0.01 uF, ceramic-disc
C10 - 47 uF, 50V electrolytic
C12 - 0.01 uF, ceramic-disc (for a direct connection)
Resistors all 1/4 W
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R1, R2 - 1 to 2 Meg
R3, R6, R9 - 510 Ohm
R4, R5, R7, R8, R10 & R11 - 1.6K
R12 - 100 Ohm
R13 - 10K
R14 & R15 - 10K, linear tapers
R16 - 500K variable resistor (for a direct connection)
Semiconductors:
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Q1 - Q4 - NTE312, N-Channel JFET or equivalent
Q5 & Q6 - NTE618, Varactor Diode
Q7 - Red 5mm LED
Other:
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28 AWG Shielded Audio cable, 4 conductor
RCA Jack, audio/video, male/female or 50 ohm connectors
PCB screw terminal blocks
Magnet wire, 16 AWG (Phase Antenna w/ 18 turns)
Litz Wire, 180/46-44 Special Blend - www.mikeselectronicparts.com/...
Ferrite Rods, Amidon R61-050-750
AM Loopstick Antenna Coil (Transfer Coil)
Mini-coax, RG178 or other...
10-inch round wooden Embroidery Hoops for Phase Antenna
Plastic Junction Box or Enclosure, 4.53" x 3.54" x 2.16"
PCB, Prototype Board
Cable Gland - Lokman PG7 3 to 6.5mm
Aviation Connector, Plug 12mm 5 Pin female/male
120VAC to 12VDC, 300mA power supply - needs to be a low noise device
Wire, solder, Furring Strips, angle brackets, 1/4" bolts, nuts, washers
1/4" threaded rod, etc.
SPDT switch - (for a direct connection)
Have fun & enjoy!
And another circuit you may find helpful below.
Oscillator Sniffer | Close Proximity AM Transmitter | Ferrite Antenna Booster
• Oscillator RF Sniffer ... 
Наука
It's Fantastic! I will definitely try to repeat this project.
Check out the playlist with more circuits I built & shared:
Build an Active AM Broadcast Ferrite Antenna /w Phase Loop
ruclips.net/p/PLjLu4V-71S1KcC5Eeoq7BXWV--xbMb7BN
Best,
Don
Love the design and functionality Don. Actually looks like some of the antennas I’ve seen in old radio books. You make great use of the pill bottles. 🤣🤣 I’ve got a bushel basket full that I’ve made all kinds of projects with. Great video.
Brad
Brad, many thanks. I saw a similar design in a article from years back and tweaked the design using empirical… I’ve since repurposed all of the components, but it was fun building and using it for a while. I appreciate you watching and reaching out. Best, Don
Nice build big thumbs up 👍
I appreciate it Allan. Thanks for watching. Best, Don
Beautiful work ... really a great project.
My compliments.
Good listening.
73. Giuseppe.
Thank you, I appreciate it. Best, Don
Wow!! Don, where do you come up with these great ideas. Thanks for the time taken to post that.
Josh - I enjoy building off what others have done in the past. Reading electronic publications from the 1930s to 1990s is something that facilitates my innovation or lack of. LOL Thanks for watching. Best, Don
Thanks for sharing your radio ideas. You do a very nice job of describing your projects.
Jeff - much appreciated. This was a little different and provided a learning opportunity for me. Best, Don
Cool
📻👍🙂‼️
Thank you Jeff. Best, Don
Great video Don. Thanks. Something I've always wondered about and you mentioned it regarding the use of two ferrite coils in parallel for more pickup. Would two identical larger loops with individual tuning caps each, both tuned to the same frequency and aligned in the same direction placed somewhat apart, then wired in parallel {or series) produce more signal than one loop alone ?
Tim, I think it would add gain and directivity to cancel out noise and other... You should build one and keep me posted on the results. Best, Don
Cool build Don ! Yahoo put all my emails in the spam folder again : ( Hopefully i can get back in the shop in a couple of months. I am looking forward to more.
All my best.
Bobby
Thank you Bobby. Good to hear from you and I hope you can get back in your shop sooner than expected. Take care. Best, Don
I think my project list just got a little longer!😂
Thanks for watching and reaching out. My playlist below with a few more circuits.
Build an Active AM Broadcast Ferrite Antenna /w Phase Loop
ruclips.net/p/PLjLu4V-71S1KcC5Eeoq7BXWV--xbMb7BN
Best,
Don
Amazing! Will this work on antique radios with an external antenna hook-up, or just radios with an internal loop antenna? Thanks.
Thank you. It works great with radios with no loop. Just attach a small length of wire to the external antenna and place the transfer (induction) coil by it and you’ll be good to go. I’ll demo this in an upcoming video. Best, Don
Thank you.@@RestoreOldRadios
Look for an new video with an update. I had an opportunity to use the external antenna jack on my Sony ICF-SW7600GR with success. One capacitor and resistor and it works like a champ. I’ll share the simple mod ASAP. Best, Don
I made the modification: Active AM Broadcast Ferrite Antenna /w Phase Loop - Circuit Modification & Next Project ruclips.net/video/QtvijeAODI8/видео.html
Seems like fantastic performance. Great work. How does this compare performance-wise to a 100’ outdoor wire antenna? Can the pill-bottle coil be replaced for simple feed to an antenna jack?
Much better than a 100’ wire antenna in my location. The directivity of the ferrite with the phase antenna allows move to reduce a lot of noise and interference from adjacent stations. Regarding the induction coil, I have not tried a direct connection, but using a low value pF capacitor should work. When time permits I’ll give this a try and let you know. Best, Don
I made the modification: Active AM Broadcast Ferrite Antenna /w Phase Loop - Circuit Modification & Next Project ruclips.net/video/QtvijeAODI8/видео.html
Great Video... impressive performance. Would you mind taking a minute to explain how the transfer coil works. It would seem that somehow it would have to be resonant with radio's antenna and have impedance characteristics to match the JFET buffer follower. So how does it just happen that an old AM loop-stick Ant coil just works so well. Do the characteristics of the mini-coax matter? Thanks again for the video.
John, thank you. You bring up an interesting point that needs further investigation. It seems having the front end of the circuit tuned to resonance, I’m only passing the selected bandwidth through the three amplifier stages to the final buffer. The transfer coil is acting as a broadband antenna as the inductance falls in your typical range for the BC band. I didn’t consider using a slug tuned inductor or adding a capacitor, but I will give this a try tomorrow and let you know if I see any performance gains. I’m not sure of the exact output impedance of the buffer, but I would think 50 to 75 ohm coax would be fine. I have seen other designs that used shielded audio cable with good results for short distances. I’ll reply back on my testing ASAP. Best, Don
John,
I just uploaded this video with my findings: Active AM Broadcast Ferrite Antenna /w Phase Loop - Circuit Modification & Next Project ruclips.net/video/QtvijeAODI8/видео.html
Best,
Don
Hi Don. Thanks for the update video very helpful.
In terms of reception, very great results, even with a so simple radio, but please Don, is this antenna system unidirectional or bidirectional?
Thank you. It’s bidirectional, but I have seen some slight differences in signal quality when rotating 180°. Best, Don
Hey Don, that's pretty cool. What did you use for those wood loops? Embroidery hoops perhaps? How far away was that station you were receiving at the beginning of the video? As Curly Howard used to say "I'll bet I could pick up The Lone Ranger on this!", LOL! Take care, Gary
Gary, you are correct on the wooden Embroidery hoops. The station in the background as I was rotating the antenna is 43 nautical mikes and operates daytime at 10kW. On average I can listen to stations within 75 miles of my house or more if they are 50kW. Night time DX is awesome. Thanks again and I hope all is well following the weather event in your area. Best, Don
She's beautiful!!!
+Bob Kozlarek WA2SQQ Tim, I would like your thoughts as well. I’m considering adding some 1N914 diodes to the input of Q1 that can be switched in as needed to reduce potential overloading the amp. Bob WA2SQQ brought up this concern, which is a valid point. Best, Don
+RestoreOldRadios, Don, I'll be sending an email in a little bit, with a few ideas...
How i can matching antenna coil with low imput impedance mean calculate number of secondary turns thank you
Salahi - check out part 1 & 2 of...
www.industrial-electronics.com/measurement-testing-com/rf_design_4.html
www.industrial-electronics.com/measurement-testing-com/rf_design_4b.html
Best,
Don
How is it “phase”? You are actually tuning the main receiving antenna to resonance. Seems it would the same for the pickup bar antennas. Very interesting project, but I wonder how all the amplification will hold up in high RF locations? Active loops are very effective for BCB DXing.
Hi Bob - I’m far from an expert and my build was trial and error with no real scientific testing. My design closely mirrors the work of Mr. Harry Helms, W5HLH (former AA6FW) who’s article on “Phasing” appeared in Popular Communications, Aug. '93. Mr. Helms had success positioning his loop up to three feet away from the active ferrite antenna. Moving the loop closer or further away from the ferrite antenna does impact the performance, i.e., on some daytime distance stations some 100 miles away heterodyne whistle is minimized or eliminated. I didn’t note much improvement in performance over ~18”. I also rotate the loop on the threaded rod leading or following the ferrite rod as needed, which I didn’t demonstrate. To your point, both antennas are tuned to be resonant with the receiving signal then tweaked by ear for the best overall reception. Loading or saturating the JFETs in close proximity to a Tx as you stated would likely occur. After giving this some thought, I was thinking of adding some diodes that can be switched in/out of the input to Q1. Any suggestions or recommendations would be appreciated. Thanks for watching and reaching out. Best, Don
Don I really appreciate your response, but not nearly as much as I look forward to your videos. You’ve taught me a few tricks and inspired me to get into a restoration mode. I’ve been doing several old National (Panasonic) radios that we’ve accumulated - I work for Panasonic, 40 years this September.
So, I really like your design. I see it as a “double tuned” front end. You could have used either the loop or the ferrite antennas by themselves and amplified their output. However, in a city “high RF” environment you would probably create an awful lot of IMD. I think the double tuned approach definitely helps.
Here’s a few design tweaks that you might want to play with - like you I’m no expert, but I have been playing with loops for about 25 years. Most recently I’ve used the PIXEL magnetic loop to receive 160m and finish up my 160m WAS (Worked all States) award. I live 2 miles from a 50kw AM station - with a conventional antenna it would be impossible.
1. Your ferrite rods by themselves are tuned to resonance (just like the antennas in a transistor radio). They typically receive broadside to the physical antenna with deep nulls of the ends. What I don’t know is whether having two in parallel, vs. end-to-end would work better? If physically parallel to each other, would winding one in the opposite phase to the other help you or hurt you?
2. If you remove the loop, I suspect you would still receive fairly good using just the two ferrite bars. I’m thinking your “loop” might be functioning much the same way that the “director” element in a yagi antenna works. The distance between the loop and the ferrite antennas controls the coupling, so by decreasing the coupling (increasing the distance) you might be able to raise the “Q” of the design. Might be interesting to see if shielding the ferrite antennas would give the loop more gain or directivity.
3. I think the loop would typically show nulls broadside, with the strongest nodes would be off the “ends”, In contrast, I think your loop-stick ferrite antennas receive best broadside. Have you experimented rotating either the loop or the ferrite antennas by 90 degrees?
4. I use a Kiwa receiving loop for more than 20 years. One of its key designs is the ability to change the angle of the sense antenna. I’m able to null local AM stations about 6-7 S units. If you don’t know about the Kiwa loop, investigate it.
Bob -
Thanks for your kind words. I really appreciate the detail in your response. I had an opportunity to try a few things today you touched on as noted below.
1. I disconnected the loop and used just the ferrite antenna and performance was degraded, i.e., more noise w/ less sensitivity.
2. I reversed this just using the loop and got the same results only less sensitivity and directivity.
3. I reconnected the ferrite antenna and placed the loop at a 90 degree angle at various distances and locations in relationship to the ferrite... After finding the best location and spacing, I used the antenna and compared the setup to the original. Very little if any performance seemed to be gained based on the new configuration other than the phase control being more sensitive to change.
4. I then reversed this setup making the loop the primary and placed the ferrite... at 90 degrees. I got the same results as aforementioned, only less sensitivity.
5. I also tried both configurations with the ferrite in the horizontal position vs. the stacked position and didn’t record any noticeable change.
I did notice while having either antenna at 90 degrees, I had two locations the signal would now peak, one in the directional pattern of the ferrite and the other being the loop. In both cases the ferrite antenna pattern seemed to provide the highest amplitude signal w/ the least amount of noise or interference.
I can’t easily try the other configurations you suggested without disassembling the antenna.
I would appreciate your thoughts on my preliminary findings.
Best,
Don
How can one obtain detailed drawings?
Shawn - the schematic & BOM: drive.google.com/file/d/1I-DjxVC_95e-Qc-CBFTY6SJ1Vk6duuba/view?usp=sharing Hope this helps. Best, Don
I going to have to replace a ferrite antenna ,the one that came with the radio I bought is in three pieces,I sent for the nearest size ferrite bar blank ,I have magnetic wire all I need is some.was to dip in on when I am done ,this G.E.radio has been a bit of fun the owner before me I pretty sure he it the tubes in the wrong place,I haven't been able to down load a schematic for my G.E.tube radio T-142-A if anyone can send me a picture that show where the tubes to go If would help me finish this radio It's pretty much done except for that .
Ron - try page 44 at: www.rsp-italy.it/Electronics/Radio%20Schematics/Collections/Beitman/1960.pdf Best, Don
By a cheap HF pre-amp to avoid building a legacy circuit.
One can do that for sure, but that takes the fun out of it and learning opportunities along the way. Best, Don