| Page 1 of 2 | 1 | 2 |
|
|
What's a better HF receive-only antenna: MFJ-1024 or a loop?
Hi,
I need broadband (2MHz - 30MHz) receive-only capability. I will be connecting the antenna to a system that can stare at 10 MHz of RF spectrum simultaneously. I have very limited space and almost no antenna experience. I've been told to look for a loop antenna. I stumbled across the MFJ-1024 active antenna. What's the best choice for my application? I want to hear very weak signals. I have limited time available to do the install. I'll gladly spend more money to have less hassle and a greater probability of success. John |
A simple wire antenna will do as good a job on the hf frequencies.
Simply run a length of thin wire around the perimeter of the largest outward facing window and attach to your receiver. Suspend it with mini suction-cup hooks. Or, run a length of wire around the perimeter of your listening room. Just tuck it between the carpet and wall and nobody will be the wiser. Thin multistrand wire is the best choice, and you can even use really thin magnet wire for the window antenna. |
The Wellbrook loops are broadband and very quiet. Bring money. I use
the ALA100 and a homemade wire loop. The other models come with loops, but are less flexible. Long wires pick up lots of man made noise. I think those vertical whips plus amp like the MFJ1024 are worse than a long wire. |
wrote Hi, I need broadband (2MHz - 30MHz) receive-only capability. I will be connecting the antenna to a system that can stare at 10 MHz of RF spectrum simultaneously. I have very limited space and almost no antenna experience. I've been told to look for a loop antenna. I stumbled across the MFJ-1024 active antenna. What's the best choice for my application? I want to hear very weak signals. I have limited time available to do the install. I'll gladly spend more money to have less hassle and a greater probability of success. John You're going to be at odds between your desires and what "very limited space" is going to allow in the way of antennas. Unless you can get some form of antenna away from the dwelling, and even better up in the air, very weak signals are not in your future. If your listening is going to be on a portable, a 10' window-area wire works fine, and so does the factory whip, if you're upstairs, LOL. Loop antennas can be very expensive, costing more than your radio, or cheap, AM Bcst band loops like Radio Shack occasionally offers. With what little information you provided, its hard to tell what you really expect, and what your price range for receivers is, or what you are using. Jack |
John,
|
|
The nice thing about the Wellbrook ALA100 is you can use it portably as
well. This is a recording I made of the LAX TIS on 530Khz from about 400 miles away www.lazygranch.com/sound/lax_530_etgravel.wav This was with the 4ft on the diagonal loop. |
|
Dave Holford wrote:
snip Loops are directional, as are dipoles etc.snip Wellbrook suggests a rotator for LW and MW on the 1530, but they don't seem to call for one for HF. http://www.wellbrook.uk.com/ALA1530.html |
Thanks for your reply.
I have a special wideband (10 MHz) SIGINT radio. I think I'm going to go for the Wellbrook ALA 300. Should I sit it on my deck or should I put it up on a mast? My gear is in my basement. John |
Sorry, I should have given more information.
I've used a B&W ACS-1.8-30 inverted vee in the past and that is way way too big. So I need something smaller than that. I like the size of the Wellbrook ALA 300. I think I'll go with that. John |
In article , Mark S. Holden wrote:
wrote: Hi, I need broadband (2MHz - 30MHz) receive-only capability. I will be connecting the antenna to a system that can stare at 10 MHz of RF spectrum simultaneously. I have very limited space and almost no antenna experience. .... Active antennas amplify everything they pick up including your neighbors lamp ^^^^^^^^^ dimmer, your crt computer monitor and possibly any VCR's you might have. If ^^^ ^^^^^^^^ you're gonna get one, I suggest installing it away from the house. Given the description of the receiver, I suspect that the OP wants to do some Van Eck monitoring. (Remote viewing of computer displays). With current computer displays better results are probably obtained in the VHF frequency range. Also, monitors are much better shielded now than they were when Van Eck wrote his paper, before the FCC cracked down on computer generated interference. The only other things I think that bandwidth in that frequency range would be good for would be hacking BPL, or making a very high resolution lightning strike detector. Mark Zenier Washington State resident |
Nope. Be able to display a waterfall graph of a 10 MHz wide portion of
HF so as to identify active transmissions/frequencies. John |
In article .com,
wrote: Nope. Be able to display a waterfall graph of a 10 MHz wide portion of HF so as to identify active transmissions/frequencies. Cool. My guess, to match your constraints, would be an amplified untuned loop. (Probably the Wellbrook if you can afford it). But I wonder, if there's no narrowband selectivity inside the box, just how sensitive you can be with that bandwidth. (The Laws of Physics and all that). Mark Zenier Washington State resident |
I believe the ability to null goes down as the loop becomes less
"small." I suspect if you made a smaller loop for your wellbrook, it would become directional again, but the gain would be lower due to smaller aperture. |
If your goal is to identify the signals, I think the vertical with amp
(i.e. Might FIne Junk 1024 or even home-brew version) will do the job. I suspect (but have no first hand knowledge) that noise sources will not be very coherent, so they won't spike a spectrum analyser like a real RF signal. If you wanted to listen to the signal you identified, then I'd go for the Wellbrook. |
Hello.
It appears that you are going to buy a Wellbrook ALA 330S Active Loop Antenna (there is no such model as ALA 300). Note that while this antenna will afford you superb reception (I recommend that you read Jay Allen's review at this URL: http://www.radiointel.com/review-wellbrook.htm), just buying it is not all you will have to do. There are other items you must purchase locally AND the antenna MUST be properly mounted and installed. (A fence-post or deck railing is a good location. An attic is an even better one. Even though the instructions mention the optimum outdoor mounting location, it is definitely not critical. I prefer attic-mounting as the antenna performs in a superlative fashion in that location and it (and its associated equipment) - no small invenstment! - is protected from the weather). If you are indeed serious, please read the following carefully. You will need to buy a suitable length of RG-58C/U (in the United States often labeled RG-58U - this is the same thing) coaxial cable (no other kind will do!) and two (2) BNC connectors. This can be purchased at your local Radio Shack. Should you wish to take advantage of the antenna's directional capabilities (recommended), you will need to purchase a Radio Shack antenna rotator (about $75.00) and the special cable for that rotator (about $15.00). You will also need a suitable length of PVC (preferably) pipe which attaches the antenna to the rotator (about $2.00 at your local hardware store). All of this MUST be hooked up in STRICT accordance with the instructions packed with the antenna. IF --- you follow the instructions EXACTLY, the installation process is quite easy and shouldn't take more than an hour or two. IF --- you feel that you are incapable of doing the installation yourself, I strongly recommend that you hire a competent electrician to install the antenna for you. MAKE SURE that he READS the instructions CAREFULLY before attempting the installation. (Installation charge will probably be between $200-$300.) You will want to contact THE SHORTWAVE SHOP in the UK if you wish to make the purchase with a credit card. You can buy directly from Andy Ikin at the factory, but he accepts checks only. (Also THE SHORTWAVE SHOP sometimes charges less.) I believe the current price in dollars, including shipping, is around $350.00. Note too that there may be a delay in shipment; Andy has been quite backed-up of late due to an overwhelming number of orders (the "word" has gotten around about this antenna!), though I think he is catching up to some extent. IF --- you are willing to go to the lengths necessary to acquire this antenna, you will be rewarded with probably the finest antenna ever designed for the shortwave listener. (The purchase "hurdles" are deliberate: Wellbrook is a "one-man" operation and Andy can make only so-many antennas!) You want to hear very weak signals? This is your antenna! I own one. In all my forty-plus years of shortwave listening, I personally have never experienced ANY antenna even nearly as good as the Wellbrook ALA 330S. Best of luck, Joe |
Joe Analssandrini wrote: Hello. It appears that you are going to buy a Wellbrook ALA 330S Active Loop Antenna (there is no such model as ALA 300). Note that while this antenna will afford you superb reception (I recommend that you read Jay Allen's review at this URL: http://www.radiointel.com/review-wellbrook.htm), just buying it is not all you will have to do. There are other items you must purchase locally AND the antenna MUST be properly mounted and installed. (A fence-post or deck railing is a good location. An attic is an even better one. Even though the instructions mention the optimum outdoor mounting location, it is definitely not critical. I prefer attic-mounting as the antenna performs in a superlative fashion in that location and it (and its associated equipment) - no small invenstment! - is protected from the weather). If you are indeed serious, please read the following carefully. You will need to buy a suitable length of RG-58C/U (in the United States often labeled RG-58U - this is the same thing) coaxial cable (no other kind will do!) and two (2) BNC connectors. This can be purchased at your local Radio Shack. Should you wish to take advantage of the antenna's directional capabilities (recommended), you will need to purchase a Radio Shack antenna rotator (about $75.00) and the special cable for that rotator (about $15.00). You will also need a suitable length of PVC (preferably) pipe which attaches the antenna to the rotator (about $2.00 at your local hardware store). All of this MUST be hooked up in STRICT accordance with the instructions packed with the antenna. IF --- you follow the instructions EXACTLY, the installation process is quite easy and shouldn't take more than an hour or two. IF --- you feel that you are incapable of doing the installation yourself, I strongly recommend that you hire a competent electrician to install the antenna for you. MAKE SURE that he READS the instructions CAREFULLY before attempting the installation. (Installation charge will probably be between $200-$300.) You will want to contact THE SHORTWAVE SHOP in the UK if you wish to make the purchase with a credit card. You can buy directly from Andy Ikin at the factory, but he accepts checks only. (Also THE SHORTWAVE SHOP sometimes charges less.) I believe the current price in dollars, including shipping, is around $350.00. Note too that there may be a delay in shipment; Andy has been quite backed-up of late due to an overwhelming number of orders (the "word" has gotten around about this antenna!), though I think he is catching up to some extent. IF --- you are willing to go to the lengths necessary to acquire this antenna, you will be rewarded with probably the finest antenna ever designed for the shortwave listener. (The purchase "hurdles" are deliberate: Wellbrook is a "one-man" operation and Andy can make only so-many antennas!) You want to hear very weak signals? This is your antenna! I own one. In all my forty-plus years of shortwave listening, I personally have never experienced ANY antenna even nearly as good as the Wellbrook ALA 330S. You've never strung up any really long wires? dxAce Michigan USA http://www.iserv.net/~n8kdv/dxpage.htm |
In article ,
"Mark S. Holden" wrote: Dave Holford wrote: snip Loops are directional, as are dipoles etc.snip Wellbrook suggests a rotator for LW and MW on the 1530, but they don't seem to call for one for HF. http://www.wellbrook.uk.com/ALA1530.html The loop will have a more directional pattern the lower in frequency you go. -- Telamon Ventura, California |
|
Any 50 ohm cable should do the trick. I'm not even sure how significant
the cable is since the wellbrook amplifies the signal. You can do all the "paperwork" via email then fax your credit card number. The weak dollar policy of the Bushies sucks big time. It makes items like the Welbrook damn expensive, and there is no other source. |
I went on BLM land and strung up about 200ft of long wire with a
Palomar magnetic balun in the center. I still got better SNR with the 30ft loop on the ALA100, and this is in an environment where there was little man made noise. I think too much is made about the strength of a signal versus the quality. You can alway use a preamp for more gain, but that generally doesn't make the signal sound any better. Signals sound cleaner on the loop. [Reminds me, I have to put that balun on ebay. ;-)] |
|
Is 300 feet long enough for you? I had one of that length very briefly
(one year) until it came down in a storm. Then I erected a 100 foot one (oriented North-South - broadside to East-West) which I used for a number of years. I was able to secure this length much better. This was all many years ago when I lived in my parents' house which had a lot of land. The Wellbrook is superior, especially in the summer, as it attenuates atmospheric noise and local electrical noise. The signal-to-noise ratio it affords is unparalleled. When I used my 100 foot wire, DXing was difficult in the summertime due to the noise and static. I believe that most people still have that problem, as well as greatly increased local electrical noise. Preamps, of course, do nothing to alleviate any of this. So yes, I have experience with many different types of antennas, both passive and active. And note that while I was answering the creator of this thread who said he had limited space, and I personally now also have limited space, I firmly believe that, even if I could, I would not go back to a longwire antenna except perhaps as a supplement to my Wellbrook ALA 330S. It is THAT good! Best, Joe |
Joe Analssandrini wrote: Is 300 feet long enough for you? I had one of that length very briefly (one year) until it came down in a storm. Then I erected a 100 foot one (oriented North-South - broadside to East-West) which I used for a number of years. I was able to secure this length much better. This was all many years ago when I lived in my parents' house which had a lot of land. The Wellbrook is superior, especially in the summer, as it attenuates atmospheric noise and local electrical noise. The signal-to-noise ratio it affords is unparalleled. When I used my 100 foot wire, DXing was difficult in the summertime due to the noise and static. I believe that most people still have that problem, as well as greatly increased local electrical noise. Preamps, of course, do nothing to alleviate any of this. So yes, I have experience with many different types of antennas, both passive and active. And note that while I was answering the creator of this thread who said he had limited space, and I personally now also have limited space, I firmly believe that, even if I could, I would not go back to a longwire antenna except perhaps as a supplement to my Wellbrook ALA 330S. It is THAT good! I'll stick with my wires, thanks! dxAce Michigan USA http://www.iserv.net/~n8kdv/dxpage.htm |
On Tue, 17 May 2005 11:48:42 -0400, dxAce
wrote: So yes, I have experience with many different types of antennas, both passive and active. And note that while I was answering the creator of this thread who said he had limited space, and I personally now also have limited space, I firmly believe that, even if I could, I would not go back to a longwire antenna except perhaps as a supplement to my Wellbrook ALA 330S. It is THAT good! I'll stick with my wires, thanks! dxAce Michigan USA http://www.iserv.net/~n8kdv/dxpage.htm Spoken like a true obstinator... |
David wrote: On Tue, 17 May 2005 11:48:42 -0400, dxAce wrote: So yes, I have experience with many different types of antennas, both passive and active. And note that while I was answering the creator of this thread who said he had limited space, and I personally now also have limited space, I firmly believe that, even if I could, I would not go back to a longwire antenna except perhaps as a supplement to my Wellbrook ALA 330S. It is THAT good! I'll stick with my wires, thanks! dxAce Michigan USA http://www.iserv.net/~n8kdv/dxpage.htm Spoken like a true obstinator... I'd compare my DX'ing totals with you any old day... dxAce Michigan USA |
The palomar balun I have is designed for center feed. It was certainly
used correctly. |
|
There is no model number on it, but it's not the MLB-1. In the dark
ages, Palomar made two other magnetic baluns, both bottoming out in the beacon band. The one I have has three eye bolts: one on the top and one on each side. You can attach the long wires to the side eye bolts, that is, they are isolated. A small white wire comes out each side which is then soldered to the long wire. The other model had some sort of control box that allowed switching between a pair of long wires. IIRC, the balun had 3 connections for long wires. You could pick a pair, which would be in a V shape rather than a normal dipole. This allowed the antenna to be electrically rotated (so to speak, since there were only 3 angles). |
|
I've done the long wire route too. The 7030 has a high impedance
connection for this purpose. The magnetic balun is superior to the long wire in that you can at least avoid the local noise generated at your QTH. The wire with the balun is still a random length. You can just tap it in the center rather than the end. Anyway, I've gone to the Wellbrook now, so I really don't care about inferior techniques. |
Joe,
THANK YOU!!! Fantastic info. I'll print and follow your instructions to the letter. I'm happy to hear that I'll get better performance in the attic than outside. The attic install is more convenient for me and I like the idea of protecting the antenna from the weather. If I need a pre-amp what would you recommend? I'm digitizing the RF with a 100 Msps 14-bit ADC with max scale at 5.5 dBm. Ideally, I'd like the signal to peak at around 5.5 dBm so I'll realize the full dynamic range of the "receiver". What dBm range should I expect from the Wellbrook antenna? Thanks! John |
It sounds to me like you are just going to digitize RF and try to find
signals. I'll put a scope on the output of my Wellbrook and see how much signal is present, but I suspect I won't see much on a scope. The manufacturer knows the antenna will be going to a receiver with gain. I'm very certain you will need additional gain before the ADC. dBM should be quite meaningless if you are just digitzing RF since there will be many signals present. [dBm would make sense if one sine wave was present.] The sum of all RF will have many sine wave, so the notion of the "crest factor" is relevant. One thing to note is that while the Wellbrook is specified for response up to 30MHz, it is picking up signals well beyond that limit. I have no trouble getting air band navigation beacons with the Wellbrook. Obviously it isn't optimal at 3x the factory spec, but you will probably have to significantly antialias the signal before digitizing. I bet it is just loaded with FM broadcast signals.You would probably benefit from adding some sort of AGC circuit too. |
"M",
|
RHF, you always provide a wealth of written and URL-referenced information
to the group, so it is with respect for your efforts that I am making some suggestions to correct a couple of your definitions : "RHF" wrote "M", . IF you have a Single 'piece' of Wire Antenna Element connected to a MLB (UnUn) along with a Ground Wire and Coax Cable. Then in general most people would call this a Long Wire Antenna; and many would more specifically call it a Random Wire Antenna. . IF you have Two Equal 'pieces' of Wire Antenna Element connected to a Balun along with a Ground Wire and Coax Cable. Then in general most people would call this a Dipole. . Dipole by Design {Tuned} : If the Two Equal 'pieces' of Wire Antenna Element are "Cut" to a specific length for a given frequency. Then the Two Equal 'pieces' of Wire Antenna Element {Together} can be said to be "Tuned" or they can be referred to as a "Tuned Dipole Antenna". . Dipole by Chance/Random {Un-Tuned} : However, if the Two Equal 'pieces' of Wire Antenna Element are simply used to fill the available space; and NOT "Cut" to a specific length for a given frequency. Then the Two Equal 'pieces' of Wire Antenna Element {Together} are simply a Random Length and can be said to be "Un-Tuned" or they can be referred to as a "Un-Tuned Dipole Antenna". . iane ~ RHF . . . . . You can leave out all mention of Baluns and Coax from your description of any kind of antenna. Baluns and Coax are not part of an antenna, they are part of the transmission line. Furthermore, neither a Balun nor Coax are required as part of any antenna or transmission line system, they are both options that provide either convenience or safety or both. You may also omit the inclusion of a ground wire as being any part of a dipole antenna. An earth ground is never part of either the antenna or feedline system of a center-fed dipole antenna. On the "random" or "long wire" terms, it has always been kind of laughable to split hairs about how long a wire is before it becomes a "long wire". Using the IEEE definition that states 2WL long for instance: for 29 mHz reception, a random piece of wire length suddenly becomes a 2WL "long wire' when its 66 feet long. Then, when we cut wire for 1/4 WL that generally fulfills a good receive and transmit capability for a given frequency, it sounds ignorant to call that a "random wire", which of course it is not. Those two terms may always cause confusion in the field. Best regards, Jack |
I suppose you could use the term untuned dipole, but I think most
people would interpret the term incorrectly. Functionally, both are random lengths of wire. In most cases, the ground connection is through some wire, which in itself is an antenna (not to mention an inductor). Since you can never make a decent connection to ground, I try to use antennas that don't require a good ground [Counterpoise grounds are the exception in that they are part of the antenna.] |
|
In article ,
dxAce wrote: wrote: I suppose you could use the term untuned dipole, but I think most people would interpret the term incorrectly. Functionally, both are random lengths of wire. If one has a dipole would it not be 'tuned' or 'resonant' on some frequency? Resonance just means that it's operating at a point where the inductive and capacitive reactances are equal. A non-resonant dipole is still picking up the signal, it just presents it as an impedance that is mismatched to the transmission line (or receiver). Mark Zenier Washington State resident |
Thanks for sharing your advice. You are exactly right that there will
be aliasing if I digitize the RF directly. I'll actually be running it through a system of bandpass and lowpass filters, amplifiers, and a programmable attenuator. This system expects a maximum input of 20 dBm. That's why I think I'll need to boost the signal out of the antenna. My customers typically use a multicoupler between the filters and the antenna, but I don't have one. I need some sort of pre-amp, but I don't know how much gain I should get to as close to 20 dBm as possible without going over ("The Price Is Right" rules). How much gain should I get in an amplifier? 20 dB, 40 dB, 60 dB? I know it's highly dependent on my RF environment, but I need to make some assumptions to at least get close. BTW, what's the right way to measure the signal level produced by an antenna? THANKS! John |
| All times are GMT +1. The time now is 07:24 AM. |
|
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com