Many thanks to SWLing Post contributor, The Professor, who shares the following review of the RFA200 external ferrite antenna:
The Tecsun R-9012 and RFA200 MW antenna (Photo credit: The Professor)
A Quick Review of the RFA200
The Professor
I’ve considered saying something here about RFA200, as I bought one of these not long after its existence was announced on this blog a few months ago, but I’ve been hesitating because I didn’t have much good to say about it. A couple of times I’ve placed it up snug up against the the top of the two Tecsun sets I have handy (the PL-310ET and the PL-880) and found that despite a lot of knob turning it had little or no effect on improving signal on medium wave stations. I was not impressed.
But I guess I’ve kind of changed my mind on that. And oh yeah, I bought another radio. It’s funny how you can talk yourself into things when you’re talking someone else into something. But after I had mentioned to a reader here the other day that the very inexpensive Tecsun R-9012 was a worthy analog DX portable, I decided to drop twenty and pick one up for myself. After all, it was about the same price as a fancy Brooklyn hamburger. It arrived a couple days ago.
So, I have been playing with it a bit over the last few days. It’s as good as the other ones I’ve had which are the same basic radio (I’d mentioned that the bandswitch slider broke in a couple of mine). It’s single conversion. The bandwidth is a little wide, but it’s a very sensitive and simple analog set.
Yesterday I was going through the AM band and remembered that ferrite from Greece, and I pulled it out recalling that in my experience some radios are more susceptible to reception improvements using passive loops than others. Maybe this ferrite bar might be similar. And sure enough, the antenna made a notable difference this time. By placing it up against the R-9012 and tuning the thing I could certainly increase signal a bit. And I could even see it in the slight brightening or steadiness of the tuning light.
So, not a total waste money after all. I would emphasize that the difference in reception doesn’t seem to be as dramatic or sustaining as you might hear with a tunable loop antenna next to your radio. But it’s not junk either. Then again, for fifty dollars shipped it is a little pricey. Twice as much as a Tecsun tunable loop antenna, and two and half times more expensive than the R-9012 itself.
I found the best way to use this antenna is to tune the radio separately first and when you find a weaker signal you want to improve physically go ahead and rotate the radio until the signal is strongest and THEN put the antenna along the top of the radio and adjust the tuning knob on the antenna. Focus in on strengthening the signal you actually hear, going back and forth until it gets strongest. If you seem to be pulling up other stations it’s because the antenna adjustment will bring in adjacent stronger stations if you move it too far either way.
I’m surely not able to pin down the science involved in exactly how these things work, but perhaps somebody can chime in on this. I’m wondering if analog radio tuning in particular is better suited to the use of these tunable passive antennas, as opposed to PLL and DSP radios?
If you buy one of these be prepared to wait. At least mine took weeks to get here from Greece. And don’t expect miracles. But it seems rather well constructed, and will probably work with some radios. The seller has a 100% rating on eBay and has all sorts of interesting antennas for sale. I’m glad to see people succeeding in that business.
Many thanks, Prof, for sharing your fine review of the RFA200! Thanks for also mentioning the Tecsun R9012–I purchased one a couple years ago with the intention of reviewing it, then gave it to teenager who expressed interest in shortwave. I don’t think I actually put it on the air myself. I do enjoy simple old school analog radio–especially when making band scans.
to explain how these things work, first it should be understood that the ferrite bar is not magnetic.
a ferrite bar antenna, in function, is sort of between a loop antenna and a solenoid.
a loop antenna is a large loop (diameter very large compared to length) with few windings that captures the magnetic component of a radio wave and translates it to electrical current in the wire.
a solenoid is a small toroid (length very long compared to diameter) with many windings that translates electrical current in the wire into a magnetic field, used to move a part.
as you know, an accelerating electrical current in the wire creates an increasing magnetic field around the wire, and since the wire is wound around a longitudinal axis, the sum of vectors is in a straight line along that axis. oscillation is just acceleration back and forth, so oscillating electrical current creates an oscillating magnetic field and vice versa.
the ferrite bar antenna is a solenoid in reverse and the purpose is not to move a part. the small cross-sectional area would not be enough to capture a significant amount of RF energy, but since some materials have much better permissivity of free space for magnetic fields, use such a material for the core and then it does capture a significant amount of RF energy.
the permissivity of free space is 4*pi*1E-7 H/m. some metals such as carbon steel and nickel are a few hundred times better, ferritic stainless steel is up to 1800 times better; but that’s not good enough for such a small area.
ferrite bar material with MgZn is up to 20,000 times better and that’s what we use.
although 99.95% iron is 200,000 times better. I don’t know why we don’t use that.
example: if the diameter if a ferrite bar antenna is 1/4″, the area is 0.0491 square inches. multiply that times 20,000 thanks to a ferrite core and the effective area becomes 982 square inches, or a diameter of 17.7″
so how does an external ferrite bar antenna such as the RFA200 enhance the reception of a normal ferrite bar antenna?
they are coupled electromagnetically.
consider one of those pictures of magnetic field lines around a bar magnet. the lines go through the axis of the magnet, and bend around outside the bar.
the external bar antenna is a closed circuit consisting of an inductor (the solenoid) and a capacitor. the circuit resonates at the frequency
f^2 = 1/(2*pi*SQRT(L*C))
that means there is energy stored in the space around the solenoid. it would be expressed as electrical and magnetic fields, much in the same orientation as a bar magnet.
when the external bar antenna is close to the radio’s bar antenna, the magnetic field vectors go through the longitudinal axis of the radio’s antenna and are translated into electrical current just the same as it does the magnetic field of a radio wave.
and vice versa, but you don’t have a radio attached to the external bar antenna.
why do some radios not respond very well to a particular external bar antenna?
because the contribution to the radio’s antenna by the external antenna is not additive. it replaces the radio’s bar antenna. if not much better to begin with, it won’t improve the radio much better.
or it could be that the length of the radio’s bar antenna impedes the magnetic field of he external bar. if too long it doesn’t fit inside the magnetic field vectors. but I’m not sure about that.
also, it is known that DSP radios simply do not respond as well to external passive antennas. I don’t know why. it’s not the programming where the DSP chip cuts the volume of faint signals in an effort to reduce background noise, because the external antenna boosts signal. it’s not lack of sensitivity becasue some of them are sensitive and the external antenna boosts signal anyway. it’s just a fact that they don’t respond well.
if you want AM DX performance, there are better radios than the R-9012 or any of these digital wonder radios. consider a Sony ICF-SW11 with a 4″ x 5/16″ bar antenna, a Grundig Yacht Boy 205 or 207 which has two seperate 2-1/4″ bars for AM and LW but aligned together effectively are both 4-1/2″, or an Eton FR-350 with a 4″ bar and has room for a 6″ bar if you want to mod it.
All,
Late last year I obtained one from Theo’s web site (https://www.sv2czf.com/rfa200.html) as the eBay listings for some of his products seem not to be all updated.
With sadness I must report a quality issue with this product which goes unanswered despite attempts to email him at both of the listed contact addresses.
When adjusting the tuning capacitor past ~~1400 KHz, there is an electrical cracking noise as you turn the knob – it is transmitted into the audio output from the radio, and sounds like a noisy volume control potentiometer. I am not sure whether the performance of the antenna is affected in this tuning range, but I suspect it might be.
In any case, were I to request a return, the round-trip shipping cost would probably be prohibitive; still this leaves an unpleasant aftertaste.
Here is a short video to show how does RFL200 & RFA200 work:
Last days I received an RFA200 (MW) and also an RFL200 (LW).
I made a short test without direct connection with a Tecsun PL-600 unit on MW and LW.
I can say that both antenna worked well 🙂
In a few days I’ll upload a video to show how the two booster works.
I have the Q stick, the TERK and the SAT commercially made loops, as well as 4 PK models. I just ordered this RFA200 hoping to use the 50 Ohm input to couple my outdoor antennas which have baluns and co-ax lines. I like the Qstick for a compact portable antenna. It does not boost signals as well as the TERK and SAT, which is alluded to in the mfg. description. If the RFA200 jack does not connect to couple an outdoor antenna to a portable without AM terminals, I will try a 3-5 turn winding over the PVC. In the photo at the top of the page, the RFA200 ferrite is some distance from the ferrite in the radio. Try it upside down on top of the radio so the two ferrites are as close as possible. And yes, these small loops don’t help the best AM portables. Results vary with lesser radios. The much larger tuned PK loops are much better.-FARMERIK
Digression: Guy, the price of lots of materials has gone insane! I suppose it depends on what exactly is in that ferrite formula: any rare earths would certainly jack it up. Also, lots of things that before were, for lack of a better term, “non-military” now are classified “dual use” and covered by “reporting requirements” and the like, so the prices have gone up or, in some cases, the items can no longer be sold in the open market. I wish I had links to this info but I’m typing this from work with a headache. 90% of this happened in the last decade or less when they finally started getting really scared of (mainly) China and Russia.
On passive ferrite loops (and air-core loops): they are basically weakly-coupled extra antennas doubling as pre-selectors. Since we’re talking ferrite cores in this case, its a fancy magnetic antenna and a bigger core (especially with more Mu / Permeability) increases your effective capture area, a big deal with big wavelengths.
My guess why they perform better with some radios rather than others: shielding of the antenna(s) in the radio(s), in the antenna assembly (metal or plastic box, especially around the cap?), and how much energy gets in at those frequencies through the radio’s whip (which, in theory, could cause some cancellation depending on delays through the 2 antennas).
Obviously a direct connection nips this in the bud, assuming the internal antenna can be disconnected (you may have to mod it).
Oh, one last thing: on that Stormwise antenna (which I’ve been eyeing and why I’m here in this post thanks to Google), the “optional” capacitor is only optional if you already have one to resonate it: otherwise you just have a very big inductance. Other than AM broadcast, you usually want to make your bandwidth as narrow as the signal will allow, which means high Q values: fortunately, Litz wire works well in this range (and I’m assuming that’s what these companies are using, but I have yet to ask).
Professor, Does the antenna jack turn off the loop-stick inside the radio? Most portables shut off the whip from the radios in the shortwave mode but not on the broadcast and long wave mode. A quick way to test would be to plug in a shorting plug into the antenna jack and listen. I have only one radio, Heath GR78 that works well with external antennas because it does not have an internal loop stick.
I have one of these Greek rods as well and have just returned from a trip collecting spectrum using it. I have found it to be totally wonderful BUT I have not been using it in its coupling mode, I have been using the direct connection (the rod also has a wired antenna port) with an AirSpy HF+ SDR. The results are amazing. For a long time, I have been looking for a very compact travel MW antenna for use with my WinRadio Excalibur, KiwiSDR and AirSpy HF+. The RFA200 fits the bill perfectly for me, I have found it to be fantastic, performing surprising well! The build quality is good, it’s super small (much smaller than I was expecting) – it’s totally travel-friendly!
Interesting that you tried that Mark. I was wondering myself how it would perform with an SDR (or communication receiver such as an AOR AR7030), using the direct connection.
Peter Wilson
I’m more interested to see how it would perform directly connected to this guys 310 and 880 with the 3.5mm connectors. Probably much better than just passively setting next to radio.
I was doing some more experimenting with this antenna this evening, and have a couple of things to add about it. For one, I powered up my current pride and joy the GE 7-2990 (a large early 80s portable similar to the Panasonic RF-2900) and found no reception benefit from using this passive antenna. Perhaps it has more of an affinity to radios that have smaller ferrite antennas inside, although it didn’t seem to do much for my Tecsun PL-310ET.
However, I remember reading that ultralight radio expert Gary DeBock mentioned that these small Chinese analog sets offer better sensitivity if you pull the antenna up from it’s horizontal resting positing and aim it vertically (but unextended). I found that doing this with my Tecsun R-9012 actually gave this tunable external ferrite more sway over reception as well. It didn’t necessarily pull weak stations out of the noise floor, but it often provided fuller audio reception for somewhat struggling signals, specifically a little more “bottom” to the sound as I was listening with headphones.
Again just to mention that I haven’t tuned one of these small Chinese analog portables for a while, but the Tecsun R-9012 is really something on AM. And having a tuning knob rather than a thumb wheel as some do is a real advantage for DXing. From here in Brooklyn WSB in Atlanta was quite strong at 750kHz and it pulled out WJR at 760kHz from under the shadow of powerhouse WABC nextdoor at 770kHz. And I also got a pretty good read on a small Rochester, NY station I’m not sure I’ve heard before, WCJW at 1140kHz.
While it doesn’t have the light up dial, fuller audio or most of the other the bells and whistles of the new CC Radio EP Pro, I think it’s safe to say the Tecsun R-9012 is probably a better set for the seasoned MW DXer, and especially at less than a quarter of the price of the fancier analog tuned DSP radio. I’d love to see somebody do a head to head comparison between the two on medium wave.
I’ve had a RFA200 for a few weeks too, and the results have been variable, as the Prof. mentions. Best results so far have been with the shirt pocket sized Sangean DT-120 and the Tecsun PL-310ET.
Did yours peak higher in the band,above 1500 khz?
Tom Servo (aka Zach) and I discovered that when a Q-Stick is used with
a PK LW Loop the coupling effect is greatly enhanced…the standard 14
inch loop performs much like the 20 inch.
It was named the Rutledge Effect in his honor.?
BTW standard PK lw loops are going for around $99 and change
currently.
Prof,your findings were similar to mine.These things work by
interacting with the receiver’s ferrite bar antenna by inductive
coupling (also called loose coupling since there is no direct
contact).
At $51 bucks delivered it’s pricey…you could do much better
for less money with a Tecsun AN-100 or AN-200 loop (but
only Anna at Anon Co. has them now).
For about 20 bucks more you can go with the Q-Stick:
http://dxtools.com/QStick.htm
It will get it done,and it does Longwave,too.
Mike,the ferrite bar antennas you found are nice
but the price isn’t…$175 each.
I thought about some too but there are way less
expensive alternatives like the ones above or a PK Loop
for Longwave.
Agree on the price. I do have Gerry’s Q-Stick Plus+ which is very portable and performs well on a suitable receiver suitably positioned.
While searching for something else (natch) I happened upon yet another unknown (to me) small Texas manufacturer of external antennas:
http://www.stormwise.com
They have products going from VLF to shortwave (up to 4 MHZ) in different physical sizes; a distinguishing feature is that the tuning capacitor is optional, and mounted external to the device across its terminals.
These look intriguing; any experience with this brand?
Stormwise used to sell plastic-encapsulated ferrite rods for long wave / medium wave use that were as long as 18 inches, for the same cost as their 12 inch model is priced now. I used one of the 18″ X 1.0″ diameter rods years ago to make a booster antenna. This was well before the Ferrite Sleeve Loop (FSL) antennas I experiment with now.
73, Guy
Correction! I’m not sure what I was first looking at on the Stormwise site, but I now see they do still carry the 1″ X 18″ ferrite rods, as well as and even bigger 1″ X 22.5″ rod. Yikes! – Pricing is $192 and $240 respectively!
When I purchased the 1″ X 18″ rod some years ago, the cost was $40… a more reasonable cost for high performance MW antenna experimentation.