Recommendation for an antenna

[shortride]

If I understand everything I've read, a magnetic loop antenna will not cover the entire .03 MHz to 60 MHz of an R75 receiver. I'll have to find out what the most polular band is and I won't be able to do that until I hook up some sort of antenna.

[Ed_Seedhouse]

Originally Posted by shortride

If I understand everything I've read, a magnetic loop antenna will not cover the entire .03 MHz to 60 MHz of an R75 receiver. I'll have to find out what the most polular band is and I won't be able to do that until I hook up some sort of antenna.

There is pretty well no antenna that will cover that range at all well. If you insist on good performance from an antenna over that range you'll probably need at least three of them and an antenna switch.

If we're talking about pure reception, a "random" length wire as high off the ground as possible and with an excellent ground or counterpoise system is pretty well as good as anything else, at least above the AM broadcast band. You don't need all that much wire either.

For AM band or below the magnetic loop is probably a better choice, and for VHF you need a properly designed VHF antenna because a random wire gets weird directionally at these frequencies.

Transmitters are much more demanding, so if you plan to get your license and a transmitter the above advice won't apply.

[shortride]

Originally Posted by Ed_Seedhouse

There is pretty well no antenna that will cover that range at all well. If you insist on good performance from an antenna over that range you'll probably need at least three of them and an antenna switch.

If we're talking about pure reception, a "random" length wire as high off the ground as possible and with an excellent ground or counterpoise system is pretty well as good as anything else, at least above the AM broadcast band. You don't need all that much wire either.

For AM band or below the magnetic loop is probably a better choice, and for VHF you need a properly designed VHF antenna because a random wire gets weird directionally at these frequencies.

Transmitters are much more demanding, so if you plan to get your license and a transmitter the above advice won't apply.

Speaking of directional. When installing a random wire in my back yard, should there be any concern for north, south, east, west orientation? An inverted 'V' antenna is omni-directional I think. Being that it's more directional, what is the advantage to a flat-top antenna for SWL?

[ridgescan]

Given your property you could run something like mine which does really well. It's a PAR ef-swl to 100' wire configured as a horizontal "L" because of space. But the most important part of this antenna according to my own experience here in my high RFI environment, is grounding
Discovering through pure experimentation, mine has two grounds-one at the antenna and one here inside. Without both grounds, I get noise at MW and HF-I need them both.
My experience when the wire was 50' random, also showed me that orientation of the wire makes little difference. Hope this gives you some ideas.

[Ed_Seedhouse]

Originally Posted by shortride

Speaking of directional. When installing a random wire in my back yard, should there be any concern for north, south, east, west orientation? An inverted 'V' antenna is omni-directional I think. Being that it's more directional, what is the advantage to a flat-top antenna for SWL?

As long as the wire length is less than about 1 or two wavelengths, directivity won't matter much. Once you get to multiple wavelengths then the antenna becomes quite directional. Use the shortest wire that gives you a decent signal. Put it as high off the ground as you can and as far away from houses and electrical wires as possible. Use a co-ax to bring the signal into the house, making sure you GROUND the outside shielding as well as possible. Don't use your house electrical ground - too noisy. Copper water pipes often work well as a ground, but you'll often need a proper ground rod, usually least two.

I have around 40 feet of 22 gauge black vinyl clad solid copper out, attached to a tree about 15 feet high. The feed point is around 15 feet away from my house and I feed the signal via TV coax to the receiver, with another coax used for grounding. It runs about 15 feet to an outside copper pipe water outlet. That's rather a long way for a ground so I use the second cable's shield to make the connection.

That's a long ways from ideal, yet from my home at the southern tip of Vancouver Island I could hear a ham on 17 meters calling "CQ" from Japan at around 15:30 PST.

Also on the Citizens Band lots of signals from Texas and one from Colorado.

Receiver is an Icom PCR 1500.

[shortride]

This helps me understand it a little better. Now I need to review it a few time to fully understand. This is a good way to explain some things. It's like going back to school. Amplitude, Period, Frequency and Wavelength of Periodic Waves | Waves and optics | Khan Academy

[prcguy]

My advice for shortride with the new R75 is put up the longest chunk of wire heading away from the house or at most buy a PAR end fed and get used to the SWL hobby before considering anything else. The initial cash spent will be low and you will have plenty of signal into the radio to hear most anything out there.

A simple wire antenna would connect to the push terminals and a PAR would use coax to the SO-239 connector. The PAR is probably a better choice since it could be less susceptible to picking up noise generated inside your house. You can also home brew something equivalent to a PAR using a 9:1 balun and some wire if cost is an issue.

Most active whip antennas are a big compromise and can be easily overloaded where the preamp inside generates IMD, raises the noise floor and fills the spectrum with signals that don't belong there. A good active whip that does not have these problems can get quite expensive and for most SWL reception a wire antenna works better on most frequencies. I have a high end active whip and it excels in the AM broadcast band and below but for general HF use my various other wire antennas work better.

Then there are the loops like the Wellbrook which has an advantage of nulling out unwanted signals but you have to turn it, plus a new one can cost more than your R75 is worth.

Magnetic loops with the large HV tuning capacitor are extremely narrow band and have to be retuned even if you move within the same band. They are also bidirectional and need to be turned broadside to whatever you are listening to plus they are not going to cover the entire HF/VLF range of the receiver.

So unless you have space constraints and are forced to use an active whip, or you need to null out a offending station start simple and it may be all you ever need.
prcguy

[Token]

Originally Posted by shortride

A general short-wave antenna comparison question.

Space being available to hang a wire antenna, is it wise to use one verses an active loop antenna or one of the other style active antennas? I get a little confused reading comparison of wire shortwave antennas verses active antennas where some of the comparisons almost sound like a contradiction. I read one comment that said that a particular active antenna reception was at least as good as a wire antenna. Other than space availability or the lack of, what are the disadvantages only of both type?

As a point of clarification, when you say “loop” antenna you are not really describing what you mean. There are 2 main types of loop antennas; physically small loop antennas, antennas that are typically less than one tenth of a wavelength like the mag loops and Pixel and Wellbrook recommended in this thread, and large loop antennas, like a full wave Skyloop. These two kinds of loops are very different from each other although they share some common features, such as lower noise than some common wire antenna designs.

The small loop has the advantage of being small and slightly directional. This directionality has a couple of useful features, including being able to null (the null of a loop is generally sharper than the peak) offending noise or stations as long as the offending signal and the desired signal are not on the same bearing from the listener. It has the disadvantage of requiring an amplifier to achieve optimal performance and is typically more complex to do really well. These loops will work in an apartment situation to some extent but are best if you can mount them out away from the dwelling to get it further from noise sources. They can be mounted on a light duty TV antenna rotor to keep the advantage of the directionality. Up high is not a requirement, but getting them up away from noise sources is a plus.

A small loop can be fairly broad banded, depending on how it is built and the amplifier used or a simple design might be very, very, narrow banded. Just keep in mind that not all small loops have the same bandwidth.

The large loop, like the Skyloop, is simple to build but might be mechanically complex (depending on what you consider complex). For example an 80 meter Skyloop, if built as a square (it does not have to be square, but I will use that example) will require laying out a square box pattern on the ground about 67 feet on a side (roughly 267 feet of wire total, exact length depends on exact center frequency you want). A pole will go at each of the 4 corners of the box, these poles need to be pretty tall, call it 25 feet minimum, and over 40 feet desired. A simple wire will make one continuous loop around the top of those 4 poles. This loop is broken at one corner of the box and the feedline attached at that point.

I find that the example above, a full wave Skyloop on 80 meters, makes a very good listening antenna from about 1.8 MHz to about 25 MHz. It is OK from about 1 MHz to about 30 MHz. As a ham antenna, being able to load it up and transmit, it is pretty good on most of the traditional bands from 80 meters to 10 meters, but not so good on the WARC bands. A 160 meter Skyloop antenna is even better in all of these categories, plus wider banded, but of course takes a box twice the size needing roughly 144 feet per side (call it 574 feet of wire total) and needs much taller poles to be optimal.

Be careful when you read things like “a mag loop antenna performs better than a wire” since this comment is incomplete and does not tell enough of the story. For example it might be better, lower noise and as high or higher received signal levels than one “wire antenna” but not another. All wire antennas are not the same, “wire antenna” is a very incomplete description of the antenna, as there are MANY different wire antenna types. Even identical antenna designs can be installed differently, one working well and the other not.

And yes you will read contradictions, frequently, by user review. If a user had a junk wire antenna installation in a high noise environment he is quite likely going to be extremely happy when he switches to one of the well made mag loops. If the user had a good wire antenna installation and never had a noise issue he is probably going to think the loop is a waste of money.

As a general statement, if you have lots of room for big wire antennas a small loop will not perform as well as what you would be able to put up. If you are space limited or do not want to deal with putting up antennas and finding what works best for you the small loops like the Wellbrook or the Pixel are very good options. On an average city lot you might find a combination of wires and such that makes you happy, but the loops are a quicker fix with the advantage of being able to null some city listener prone noise sources.

Wire antennas of various types can be built for a few dollars each. I say experiment and try them out before dropping a chunk of money on a loop, maybe you will find something that you like. On the other hand, the better loops do work fairly well, and are easy to set up, if not cheap to buy.

I have a mag loop here, home brew but I have tried a Wellbrook also. I sometimes use the mag loop for LW/MW coverage (mostly because it nulls unwanted stations) and to determine direction of signals, again using the null, below 10 MHz (above 10 MHz I have other antennas to determine the direction of a signal). However I really don’t use that loop often, generally I am on a wire antenna of one kind or another.

In my case I have never found a small loop that I really like, as a general purpose listening antenna, as well as several of my wire antennas. But, I also live in a pretty quiet location with regard to noise and I have thousands of feet of wire up in half a dozen dedicated listening antennas, and more in my ham antennas (although some antennas do double duty).

T!

[Token]

Originally Posted by prcguy

My advice for shortride with the new R75 is put up the longest chunk of wire heading away from the house or at most buy a PAR end fed and get used to the SWL hobby before considering anything else. The initial cash spent will be low and you will have plenty of signal into the radio to hear most anything out there.

I second this strongly. Put up a chunk of wire and gain some understanding of the bands and what you want out of the hobby before dropping another big chunk of change. Unless, of course, the cash is not an issue, but then you should buy more/better receivers as well as a large tower and several antennas

T!

[shortride]

Originally Posted by prcguy

My advice for shortride with the new R75 is put up the longest chunk of wire heading away from the house or at most buy a PAR end fed and get used to the SWL hobby before considering anything else. The initial cash spent will be low and you will have plenty of signal into the radio to hear most anything out there.

A simple wire antenna would connect to the push terminals and a PAR would use coax to the SO-239 connector. The PAR is probably a better choice since it could be less susceptible to picking up noise generated inside your house. You can also home brew something equivalent to a PAR using a 9:1 balun and some wire if cost is an issue.

Most active whip antennas are a big compromise and can be easily overloaded where the preamp inside generates IMD, raises the noise floor and fills the spectrum with signals that don't belong there. A good active whip that does not have these problems can get quite expensive and for most SWL reception a wire antenna works better on most frequencies. I have a high end active whip and it excels in the AM broadcast band and below but for general HF use my various other wire antennas work better.

Then there are the loops like the Wellbrook which has an advantage of nulling out unwanted signals but you have to turn it, plus a new one can cost more than your R75 is worth.

Magnetic loops with the large HV tuning capacitor are extremely narrow band and have to be retuned even if you move within the same band. They are also bidirectional and need to be turned broadside to whatever you are listening to plus they are not going to cover the entire HF/VLF range of the receiver.

So unless you have space constraints and are forced to use an active whip, or you need to null out a offending station start simple and it may be all you ever need.
prcguy

Which bands are the most active and would benefit the most from which length PAR end fed wire antenna? Keeping in mind that my R75 has a 50 ohm and a 500 ohm antenna connection. I get a little confussed about which connection to use for which antenna.

[nickcarr]

You'll only use the coax connection.

[shortride]

Originally Posted by nickcarr

You'll only use the coax connection.

Since your answer is so short, I have to ask why the coax connection?

[Token]

Originally Posted by shortride

Which bands are the most active and would benefit the most from which length PAR end fed wire antenna? Keeping in mind that my R75 has a 50 ohm and a 500 ohm antenna connection. I get a little confussed about which connection to use for which antenna.

If you feed the antenna with coax you are going to use the 50 Ohm connector on the rig. This is because coax is most often either 50 Ohm or 75 Ohm and you want to be as closely matched to that impedance as possible. An antenna may not be 50 Ohm, but if not it will probably have a transformer to match it to 50 Ohm coax.

Which bands are most active? That is not a simple question to answer.

HF/SWL is really from 30 MHz down to just above the AM broadcast band at 1.7 MHz. Yeah, HF is really 3 to 30 MHz, but there is some activity between 1.7 and 3 MHz that can be interesting. Above 30 MHz becomes more of the scanner type world, with most transmissions being FM and public service type stuff. So I am going to talk about the range of 1.7 to 30 MHz.

Across this range you will find many, many, signals. Broadcast, military, ham, utility, etc. All of these types of services will have multiple bands across the range. Some frequency charts:

Big chart, a lot more coverage than just HF:
http://www.ntia.doc.gov/files/ntia/p...3-allochrt.pdf

US Ham bands here (including VHF and UHF):
http://www.arrl.org/files/file/Hambands_color.pdf

SW Broadcast bands:
http://modernsurvivalblog.com/wp-con...band-chart.gif

You will also find signals between each of the defined bands for these services. So, as you can see, the entire range from 1.7 to 30 MHz has the potential to be in use. Really you have to plan for working with that entire range.

With all of that said, you will find that certain frequencies are “active” for you at certain parts of the day, this is caused by propagation. Some bands are nighttime bands, some are daytime bands. As a general guideline below 10 MHz is nighttime use, above 10 MHz is daytime, but that is not a hard, fast, rule. The further you get away from this rough dividing line the more true it becomes. During your local daylight hours the bands around 3 and 4 MHz are going to be essentially dead, while at night, generally, the bands up around 25 to 30 MHz will be dead. The range from 8 to 15 MHz might be somewhat active, but to different regions of the World, both day and night.

On the nighttime active bands remember that you must have a dark path to the source, both you and the source must be in darkness or just before / after darkness. The same thing goes for the daytime bands, both you and the source must be in daylight or just before / after daylight.

T!

[nickcarr]

Originally Posted by shortride

Since your answer is so short, I have to ask why the coax connection?

Par Electronics EF-SWL End Fed Dipole SWL Antenna. Par EF-SWL.
Coaxial Cable, Coax Cable Preassembled

Just buy the above PAR antenna and 50ft (or whatever you need) length of RG-8x coax from Universal and do what they show here:



Later on you can experiment with getting the wire higher and/or further away from the house. Height is important but distance from noise sources is even more so.

[ridgescan]

To add to what has been shown by Nick and Token, I still say grounding is very important. You may get very discouraged off the getgo if you're not well grounded for RFI and swamped with noise. This PAR I have was lousy without decent grounding. RFI not only swamped the bands, it also injected the signals so you could barely make out voice. So if you do get a PAR, we can fish out some sufficient groundpoints at your home there. If you do what Nick said and can get the PAR away from the house and also away from power sources, you may only need the shield ground option. That'd be sweet.

[nickcarr]

Originally Posted by ridgescan

To add to what has been shown by Nick and Token, I still say grounding is very important. You may get very discouraged off the getgo if you're not well grounded for RFI and swamped with noise. This PAR I have was lousy without decent grounding. RFI not only swamped the bands, it also injected the signals so you could barely make out voice. So if you do get a PAR, we can fish out some sufficient groundpoints at your home there. If you do what Nick said and can get the PAR away from the house and also away from power sources, you may only need the shield ground option. That'd be sweet.

One step at a time Ridge... go easy on the guy.

[ka3jjz]

Why? We like to see members with their eyes crossed (chuckle)...

Short, one solution used by many top DXers is to have more than one antenna of different types available. The advantage to this is obvious- propagation may be playing tricks with the signal you're trying to hear, and while it might not come in so well on one antenna, it might on another. I've noted exactly this phenomenon on many occasions, even being restricted to indoor antennas.

Or you could have 2 antennas of the same type going in different directions - to keep it simple, one going N-S, the other E-W, for example.

There are many possibilities, limited only by your wallet, amount of space you have available (and you've got a bunch to play with there), and you're ability to build.

Mike

[ridgescan]

Originally Posted by nickcarr

One step at a time Ridge... go easy on the guy.

Like usual I'm getting too exited for his own good

[shortride]

Originally Posted by ka3jjz

Why? We like to see members with their eyes crossed (chuckle)...

Short, one solution used by many top DXers is to have more than one antenna of different types available. The advantage to this is obvious- propagation may be playing tricks with the signal you're trying to hear, and while it might not come in so well on one antenna, it might on another. I've noted exactly this phenomenon on many occasions, even being restricted to indoor antennas.

Or you could have 2 antennas of the same type going in different directions - to keep it simple, one going N-S, the other E-W, for example.

There are many possibilities, limited only by your wallet, amount of space you have available (and you've got a bunch to play with there), and you're ability to build.

Mike

When would one use the wire hook up on the back of the R75 receiver?

[shortride]

Is there anything special about the enclosure that houses the SO-239 other than the 9:1 transformer and having a ground terminal on it and having a way to anchor it? I probably could have one built cheaper than buy one.

Does anyone have a source for this type of enclosure? Can you buy transformers already made up? The wire and insulators aren't a problem.