New to the forum, hoping that perhaps someone can knock out a little issue that's has been at me lately.
I used to dabble in FM and liked it a good deal. However, I wanted to move to the AM band for better range and a less crowded area (In my local market, even at night). My frequency of interest lies at 1700 or 1710 Khz.
What kind of antenna should I be looking for? I will be using an Arch Linux machine with a BladeRF or HackRF acting as the exciter, and possibly and amplifier and filtering if this works well enough.
I already have a pretty stellar line feed. Using two processors, Stereo Tool with custom settings, with a high bitrate virtual cable that feeds into BBP which has some tweaks and cuts the audio bandwidth to 7.5khz (Mono). (Anything below is just to muffled to make work).
If you need some more info, let me know. Hopefully this is enough to at least get me pointed in the right direction. Thanks.
There are other far more technically minded members in this Forum who are able to help, but my own experience as an inv. L or Marconi user makes me suggest you can also use one.
If you can, use a vertical, the longer the better, and add a top load, "top hat", and, of course a tuning unit of some sort.
I am using a C-L-C type antenna tuning unit together with a variometer, and the antenna itself consists of a 20 m slant wire (I couldn't get those 20 m entirely vertical)connected to a [long, vy. long] "top hat", 45 m (!).
There are other far more technically minded members in this Forum who are able to help, but my own experience as an inv. L or Marconi user makes me suggest you can also use one.
If you can, use a vertical, the longer the better, and add a top load, "top hat", and, of course a tuning unit of some sort.
I am using a C-L-C type antenna tuning unit together with a variometer, and the antenna itself consists of a 20 m slant wire (I couldn't get those 20 m entirely vertical)connected to a [long, vy. long] "top hat", 45 m (!).
73, Carlos.
Great answer. I would also go with a similar antenna if you want to get the most bang for your buck. When it comes to medium wave broadcasting there tends to be only two antennas that actually work well for pirates and that is the inverted L or Marconi T.
Inverted L will give you a bit of horizontal polarization which can be nice if you want to get out some skywave at night and have the power to do it, Marconi T is nice for a shortened vertical monopole that will get you out nicely during the day. Windom antennas are like a cross between the two.
One other option is a full 1/2 wave dipole but that requires a lot of space and only useful for night broadcasting.
The largest challenge is to get more than a hundred feet of wire into the air and then properly tune it up to resonate. I do not want to sound discouraging because it is REALLY fun to get on medium wave, but just keep in mind the science down at those frequencies tends to be very different from that of shortwave and up.
To be honest, I don't really like to refer to "inverted L", but I did because this name is more widely known.
To Jowijo:
The issue here is that a T and an inv. L are almost the same: while the latter has "one leg" acting as "top hat", the former has an even portion of wire serving the same purpose. Also, Kage said it all - "playing" on MF is *not* the same as on VHF-FM where it's f a r easier to make an antenna, be it omnidirectional or directional.
Back to Kage... to say or rather to ask whether your comment about the inv. L having a bit more horiz. polariz. resides on the fact that the "top hat" does that when it's a long one.
I suspect it does as mine always exhibited some directivity "à la" Beverage on HF fqs like the 6 MHz<>49 m.
Well, back to my evening's DX session: I finally heard the ID of the Dutch stn on 1633 - R.Barcelona, now with an improved signal.
I forgot to add yet another word or two about another sort of antenna you referred - the dipole. Needless to say it demands a lot of space, *but*, even if one has it, what about the height above the ground?
Installing a dipole may be "easy", if one only considers the space, but if a horiz. dipole is too low above the ground relatively to the wavelength is's supposed to work on, then the antenna behaviour is highly disturbed.
A low dipole erected too low will send the signal on a too steep angle causing the signal to be useless on short / medium distance. Conversely, it may receive signals that arrive on vy. high angles.
I had a similar experience for years on end with this inv. V formerly consisting of two portions of 21 m; a few months ago, I shortened it to just two portions of 15 m, and lowered it a great deal. This is fed with 450 Ohm "ladder" line into a home made transformer inside the house (which is in many cases not a good idea, even if the antenna is used for rx only, which is the case). So the current dimension suits the 60 m<>5 MHz band.
The result after shortening the wire and lowering the whole thing was evident. Reception from the beams it's serving (SAm / Asia) improved a lot. Of course, it also serves the 31 m<>9 MHz band in particular.
I really can`t say much on the dipole when using at those low of frequencies. I just know that many medium wave pirates have used that successfully and is really a good option (so I hear) if they want to get their signal out at night across the country. Really though any horizontally polarized antenna is the best option for making skip at night. If you only want local service then stick with daytime broadcasting on a vertical with a top hat like the L or T antenna. That is not to say you can not make skip with a vertical, after all the legal clear channel broadcasters make it out fine at night but then they are using many thousands of watts.
There was one "tiny" mistake in the description of my current inv. V - maybe you noticed -, so I have just corrected my text accordingly.
The main band for this antenna is 60 m, not 31 m as I put it. The problem whn using similar aerials for harmonic fqs is the amount of lobes one gets meaning this one in particular has a good array of them on 31 m.
As for MF, I wonder what sort of aerials many of the MF pir. stns I can get actually use: inv. L or T? Perhaps as they're the most common, but possibly plain verticals, like the huge majority of the b/casters you mentioned.
Speaking of them, this page is particularly interesting and useful: waniewski.de/id208.htm
"Thousands of watt". Well, even a 1 kW MF b/caster can be heard thousands of km away. I don't mention less than 1 kW for practical reasons, but in Europe alone, the several hundred watt stns of b/casters like Gold, Absolute R and a few others incl. BBC locals from GB are regularly audible by me. One of the funniest things recently is this stn I keep receiving on 1386; lists indicate the British stns using this ch. are all 1 watt! No ID so far.
Also, trans-Atlantic reception of MF stns using 1 kW or less is possible, and if you go to the NDBs on either LF or MF, then power is certainly in the order of a few hundred watt only. Now that I mention NDBs, one of the latest casual catches was this Brazilian oild rig NDB off São Paulo state, Brazil, 1645 kHz, call MLZ, obs'ed. several times after 11 Aug around 2200 UTC. They do have a few operating above 1610.
Some very interesting and informative discussion here. Appreciate it. I'll likely go the "T" type antenna for daytime use and then search around for the best night-time solution, I really only want local coverage, anything beyond that is a bonus.
Yeah, totally new to medium-wave. Mostly VHF and UHF, and only listen to and study shortwave on my spare time so this is all some nice info to have now before I wind up dumbfounded later.
If space for an antenna is an issue, or if, as you say, local coverage is your goal (well, it also depends on "how" local you mean!), then note a MF antenna may be quite short indeed. Even LF ones can, all depending on the compensation they have in order to be able to work on the freq. they're cut for.
Of course, what you see on the photo is not only short but also compliant with actual radio regulations, viz. those of the USA.
If the latter part of my sentence is not an issue, just consider the physical aspect of the monopole. If space is not a problem, then you should use it.
I have talked to a medium wave pirate (won`t spill the beans on who) who gets out really good at night across the US using around a thousand watts into a horizontal dipole. This person suggested to me that this is the best way to get a signal out at night on the dial.
It really depends on the kind of coverage you want. If you want to cover only your local and surrounding towns then use a T antenna. Vertical polarization is the way to go for groundwave work for daytime AND nighttime. It is possible to put out skip at night on a vertical but nowhere near as likely as with a horizontal dipole.
If it is skip you are aiming for and not local coverage then the dipole is the way to go, however this antenna will not be very useful for daytime coverage.
Inverted L antennas is where things start to get interesting. Hams use them all the time on the low bands and they have the ability to shoot skip with the horizontal part and still get good groundwave with the vertical part. However because half the power is going horizontal and the other half vertical you will need more power to achieve either skip or local coverage, but put together you get the best of both worlds for all around general coverage. That is why I opted for the inverted L for my medium wave setup.
Another advantage of the inverted L is that it makes a great SWL antenna when not being used for broadcasting.
I say if you have the space, or have a portable transmitter and want to get a signal out of your local coverage area then setup a dipole, either end fed or center and up as high as possible and broadcast at night. If you want local coverage only, go with the T. If you want something inbetween that has both benefits but at a potential slight gain loss then go with the inverted L.
Also keep in mind that the inverted L has a slight extended vertical polarized lobe facing the direction of the horizontal section, so it has slightly more gain in one direction, probably only by a decibel or two. Ground radials will also affect directivity slightly favoring the direction of the radials if you only have a few laid down. More radials = more effective antenna. Get as much metal on the ground as you can with the L or T antenna. Dipole does not require radials of course.
In here www.qsl.net/aa3rl/ant2.html, one can see that several comparisons taking 7 MHz as an example, but this can be extrapolated to, say 1650 kHz, meaning a small fraction of this wavelength demands a very tall dipole. Of course, if this no problem, and also if one wishes to beam the signal on two opposite directions, then maybe the dipole for 1.6~1.7 MHz is not too unpractical.
Maybe I switch from inv. L "mode" to T "mode", at least for an experiment, but unfortunately the 2 "arms" of the T can't be horizontal, they must be installed in a slant manner due to space restrictions.
However, I could perhaps make a lower T and then have its arms horizontal or nearly horizontal.
Would you recommend me to try it, or do you think it's a complete waste of time & effort, if the vertical leg of the T is no longer or taller than, say, 10 m or a bit less?
One more item in this post: what about a [necessarily short for obvious reasons] folded monopole? I wonder whether any pir. stns. ever tried this, or if so whether some are actually using this sort of vertical.
I am really tired so lets see if I can reply with a decent answer lol...
For broadcasting I would go with the T hands down for local work. The inverted L really only has any benefit in the horizontal polarization which if you don`t have much horizontal area then it is a waste to even try to get some horiz. out of it.
So just stick with the T style antenna. The whole idea of the top part of the T antenna is a capacitance hat. The more wire up there the more current rises towards the top of the aerial. So what you want to do is get a few wires going horizontal all connected together with the vertical going center of them.
Think of the top as a compressor, the more area up there the more it squishes your signal into usable radiation. So more wire at the top to get that top hat, the more current and thus get your signal out further.
Height is always an issue with T antennas. Get it up as high as possible like any vertical. The thing to keep in mind is that a T antenna is a vertical monopole and works exactly as such. However a single piece of wire strung vertically will not perform anywhere near as well as one with a top hat horizontal section to raise current near the top.
30 feet in the air is enough to get good ground wave coverage during the day. In fact if you lay out some radials and have a good ground system you can expect to get 5+ miles with 5 watts. Your effective radiation will only be a fraction of what you put in, possibly in the order of 1/10 the power but that is still plenty of power to get a good signal out. When it comes to short antennas at MW this is really the antenna to go with. Is it efficient? Hell no. Does it work good? YES.
Short antennas look terrible on paper but work better than expected in real life.
On the folded monopole I can not help much. I have not experimented enough with that setup. I imagine it would be very useful if you already have the metal structure and want to work with it. Otherwise it seems like a waste of time?
Hi before cosnidering what antenna you could use at AM band, you must clarify if you're in US or any other country that gives you the right to broadcast under specific limitations, such as those that apply under the US Part 15.219 Rules. If you are, and want to follow the rules then the Am antenna you should use could be anyone that is under a 3m total length, as those rules say! If you don't care to go by the rules, then, an inverted V is an excellent antenna! Then we have the inverted L, and even a vertical top hat loaded antenna! All have their benefits and limitations. So you should first decide what is your target coverage area! Then find how much space you have available there, and third & in some cases much more important, if you need to be a "low profile" from common eyes antenna type! Then... you will find which is the type that fit to your needs better!
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