Ferrite rod antennas?

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ka3jjz

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If you're into homebrewing and like to work with ferrite rods, these are interesting projects. The first is MW only, and the second includes some HF coverage. Certainly a possibility if you are in a hi rise or have nowhere to put an antenna. These come from SWLing.com



Mike
 

prcguy

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I ran across this guy and he has a lot of data on ferrite rods, how many turns are needed to resonate and how many turns for the pickup loop for various bands. This video concentrates mostly on the AM BCB and he has other videos covering different SW bands. The key to his projects are huge ferrite rods you order from Russia and they provide big reception.

I built a copy of his AM BCB version and its phenomenal. I made a PVC pipe mount that rotates and tilts allowing the maximum nulling if needed. I also bought a nice FET push pull low noise preamp that covers VLF through HF with about 15dB gain and that really works well with the ferrite rod antenna.
 

PDXh0b0

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I ran across this guy and he has a lot of data on ferrite rods, how many turns are needed to resonate and how many turns for the pickup loop for various bands. This video concentrates mostly on the AM BCB and he has other videos covering different SW bands. The key to his projects are huge ferrite rods you order from Russia and they provide big reception.

I built a copy of his AM BCB version and its phenomenal. I made a PVC pipe mount that rotates and tilts allowing the maximum nulling if needed. I also bought a nice FET push pull low noise preamp that covers VLF through HF with about 15dB gain and that really works well with the ferrite rod antenna.
love that guys youetube channel
 

prcguy

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Yea, he's a real gem. I also started making a wider band SW ferrite rod antenna, same rods but different windings. Right now the highest tunable freq is about 4MHz and with a 365pf variable you use several fixed caps switched in and out to take it down to the AM BCB. I can also switch in fixed caps and take my AM BCB version down to the VLF range.

love that guys youetube channel
 

ka3jjz

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Should be a pretty decent 120 and 90 meter antenna. Good on 160, too. Those are bands that most cavedwellers - myself included - would give their eye teeth to hear without getting blasted by somebody with a plasma tv....Mike
 

DennisCA

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Interesting design. I have lots of space, but I am looking for a compact and sturdy antenna that can be mounted on my roof and be outside all year round. This compact design looks like it can survive some abuse.

I am interested in building or buying a receiving antenna for the LW/MW/SW reception and the MLA-30+ was looking like the prime candidate. The loop looks a bit flimsy though, compared to this design. I wonder how they compare.
 

prcguy

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Several years ago I made a passive 1m shielded loop using RG-11 for the loop and a small metal box to mount female F connectors and hold a 4:1 balun. It worked ok but needed a preamp and the few times I used it I attached a small low noise VLF/HF amp on the 50 ohm side of the balun and that worked well. I recently saw an assembled balanced preamp board made for loop antennas on eBay for $18 and picked one up with its companion bias Tee. This board connects directly to the loop without a balun.

I replaced the 4:1 balun in my loop with the preamp board and used an existing bias Tee from another antenna and the loop came alive and worked great. I need to spend more time with it but I think its a winner for anyone wanting to build their own loop. Here is a link to the preamp board and the same guy has bias Tees and other project boards. HF Receiving Loop Antenna Amplifier - Amateur or Shortwave SWL - Updated! | eBay

Interesting design. I have lots of space, but I am looking for a compact and sturdy antenna that can be mounted on my roof and be outside all year round. This compact design looks like it can survive some abuse.

I am interested in building or buying a receiving antenna for the LW/MW/SW reception and the MLA-30+ was looking like the prime candidate. The loop looks a bit flimsy though, compared to this design. I wonder how they compare.
 

DennisCA

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What about making a loop from something stronger than coaxial cable, like a copper pipe rolled into a 1m loop perhaps? Or an aluminum pipe? I could make such a loop at home.

Or are the properties of the RG-11 key to that antenna working since it's an insulated & shielded cable? I am just starting out and am more familiar with fabrication than RF stuff.
 

prcguy

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For an untuned receiving loop the impedance is in the 200 ohm range and you can use anything from 22ga wire to 3" copper pipe with little difference in reception. When using coax for a basic loop the outer shield is the only conductor used. My loop was a shielded version where the coax shield is grounded to a metal box on both ends and the very center of the loop has the shield severed. Both ends of the center conductor are then used as the hot portion of the loop and connect to the preamp or balun. This type of loop is a little less sensitive but with the eBay preamp it seems to be working very well.

What about making a loop from something stronger than coaxial cable, like a copper pipe rolled into a 1m loop perhaps? Or an aluminum pipe? I could make such a loop at home.

Or are the properties of the RG-11 key to that antenna working since it's an insulated & shielded cable? I am just starting out and am more familiar with fabrication than RF stuff.
 

ka3jjz

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All this loop stuff has taken us a bit astray (ahem) from the Ferrite rod topic....however...

DennisCA, there is a Facebook group that talks about mods to the MLA30 series - including using materials other than wire for the loop element.

Not sure how far down in LW you want to go, but our Loops wiki has a tremendous listing of various models, apart from the Chinese MLA30, as well as the link for the Facebook group above....


Mike
 

prcguy

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Its easy to buy or make a broad band loop that has very good performance (SNR) from VLF through HF. A ferrite rod antenna needs to be tuned to your operating frequency, usually with a variable capacitor. A typical ferrite loop has a primary winding which along with the variable capacitor make a parallel resonant circuit and the coil around the loop is usually fixed, limiting its potential frequency range. You can use less turns making the ferrite rod resonate at say 4MHz with minimal capacitance, then add fixed capacitors across the variable capacitor to increase the tuning range, but at some point the ideal C to L ratio is way out of whack and you reach electrical limitations.

An untuned loop on the other hand just works and works about the same across its entire frequency range which can be 50KHz to 30MHz for some models.

I'd still be curious about a ferrite rod antenna, but which is more suited for the range of 500khz to 30mhz ?
 

MUTNAV

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What about making a loop from something stronger than coaxial cable, like a copper pipe rolled into a 1m loop perhaps? Or an aluminum pipe? I could make such a loop at home.

Or are the properties of the RG-11 key to that antenna working since it's an insulated & shielded cable? I am just starting out and am more familiar with fabrication than RF stuff.


One of the older ARRL antenna books had design information for a nice loop made out of 3/4" copper pipe
that probably should be able to perform well.

Also, if your looking for 160 meters, there was a transmitting loop made of 3" aluminum pipe (with a really narrow bandwidth) for 160 meters. I believe the title was " Elevated Magnetic Loop for 160 & 75 Meters " It sounded a little dangerous when run with high power though.

I can't find the article in the usual places on the internet, this has the actual article (for now, I don't know how long things like this will last).


If you prefer fabricating things, these are pretty good sources for some information.
 
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