Long wires and antenna matchers

[shortride]

Antenna tuners is a little misleading so I'll just call it an antenna matcher because I think that's what it really is isn't it? Using a long wire on an ICOM R7100 receiver, which antenna matcher would anyone recommend? I don't need to buy one with a meter because there will not be any TXing going on. With the wide band coverage of the R7100 wouldn't an antenna matcher just need a band selector and a tune knob? You just monitor the signal meter on the receiver while tuning correct?

 

[k3cfc]

Antenna tuners is a little misleading so I'll just call it an antenna matcher because I think that's what it really is isn't it? Using a long wire on an ICOM R7100 receiver, which antenna matcher would anyone recommend? I don't need to buy one with a meter because there will not be any TXing going on. With the wide band coverage of the R7100 wouldn't an antenna matcher just need a band selector and a tune knob? You just monitor the signal meter on the receiver while tuning correct?

As far as i know no tuner/matcher is needed. just use the recommended antenna and you'll be just fine.


K3CFC

 

[ka3jjz]

Keep in mind that a 'long wire' (a true longwire - one word, not 2 - is a very different animal) becomes more directive off its ends the longer you make it.

On HF a simple inverted L with a 9:1 transformer will do you just fine - no need to get fancy

Mike

 

[Ed_Seedhouse]

Antenna tuners is a little misleading so I'll just call it an antenna matcher because I think that's what it really is isn't it? Using a long wire on an ICOM R7100 receiver, which antenna matcher would anyone recommend? I don't need to buy one with a meter because there will not be any TXing going on. With the wide band coverage of the R7100 wouldn't an antenna matcher just need a band selector and a tune knob? You just monitor the signal meter on the receiver while tuning correct?

A tuner probably won't help much, if at all. Yes, you will hear more signal if you tune - BUT you will also hear more noise. And what counts is how strong the signal is compared to the noise. A tuner won't change that.

Modern receivers are exceedingly sensitive and a wire about 15 feet long is all you need with one. What matters more is how high it is off the ground (the higher the better) and how far it is from sources of radio frequency noise (and your house is a major source of that).

Transmitting changes things because you need a good impedance match to avoid wasting power or, even worse, getting strong RF signals in the shack. So unless your antenna is resonant on the transmission frequency you need to tune it to match impedance.

But with a receiver, so long as you can hear the signal that's the best you are going to do. Adding a preamp or an antenna match will amplify the noise as much as the signal. If the signal is noisy already and you can't move the antenna, make sure you have a very good ground or a radial system or counterpoise.

I have 30 feet of wire about fifteen feet off the ground. Connecting the ground terminal to a counterpoise made of 40 feet of co-ax shield drops my noise figures considerably.

 

[shortride]

A tuner probably won't help much, if at all. Yes, you will hear more signal if you tune - BUT you will also hear more noise. And what counts is how strong the signal is compared to the noise. A tuner won't change that.

Modern receivers are exceedingly sensitive and a wire about 15 feet long is all you need with one. What matters more is how high it is off the ground (the higher the better) and how far it is from sources of radio frequency noise (and your house is a major source of that).

Transmitting changes things because you need a good impedance match to avoid wasting power or, even worse, getting strong RF signals in the shack. So unless your antenna is resonant on the transmission frequency you need to tune it to match impedance.

But with a receiver, so long as you can hear the signal that's the best you are going to do. Adding a preamp or an antenna match will amplify the noise as much as the signal. If the signal is noisy already and you can't move the antenna, make sure you have a very good ground or a radial system or counterpoise.

I have 30 feet of wire about fifteen feet off the ground. Connecting the ground terminal to a counterpoise made of 40 feet of co-ax shield drops my noise figures considerably.

So if I have an omni-directional D3000N antenna and also want to use a longwire antenna, I will need an antenna selector switch correct? My R7100 only has one 50 ohm connector.

 

[ka3jjz]

Most likely - however, before you go overboard, let's keep something in mind here. The 7100 only goes down to 25 Mhz - that's only going to get you things like CB, 10 meter ham, and some broadcast feeders. There's not much, if any, broadcasting happening on 25.5 - 26.1 Mhz (the so-called broadcast 11 meter band) right now. It's winter in the Northern Hemisphere, and propagation on this band, similar to what it is on CB, is not going to support long distance DX all the time.

Therefore you might consider, instead of a long wire, an antenna that is resonant on these frequencies. A simple quarter wave wire (the formula is 234 / f(mhz) where f(mhz) is the frequency in Mhz) will be fairly efficient from 25 -30 Mhz. There are many other antenna designs that can be retuned with the use of some simple math. Even the lowly dipole would work reasonably across the entire range.

The ARRL Antenna handbook is a fine place to find some really cool designs - as is this...

HF Antennas - The RadioReference Wiki

Mike

 

[Ed_Seedhouse]

So if I have an omni-directional D3000N antenna and also want to use a longwire antenna, I will need an antenna selector switch correct? My R7100 only has one 50 ohm connector.

Yes, an antenna switch would be best practice. These extremely wide band receivers really need at least two antennas, maybe more if you want to DX on AM or below. The discone won't work well below around 25 mhz. A long wire gets messy at VHF and above because it's longer than the wavelengths and directionality varies all over the lot, depending on various factors such as how straight the wire run it. It wouldn't blow the receiver if you connected the two together though, and if you don't have a switch handy you could try it.

 

[ka3jjz]

The 7100 doesn't go below 25 Mhz, Ed...Mike

 

[shortride]

Yes, an antenna switch would be best practice. These extremely wide band receivers really need at least two antennas, maybe more if you want to DX on AM or below. The discone won't work well below around 25 mhz. A long wire gets messy at VHF and above because it's longer than the wavelengths and directionality varies all over the lot, depending on various factors such as how straight the wire run it. It wouldn't blow the receiver if you connected the two together though, and if you don't have a switch handy you could try it.

I just happened to have an MFJ-1704 four-way antenna switch I used with my CB base station setup. I've got about 100' of open sky north to south and about 90' east to west.

A D-3000N antenna should do 11 meter right?

 

[ka3jjz]

Yes, although how well would be open to debate. I'm not sure how tall the center element on that discone is...

Re the MFJ-1704 - coax switches that work well on freqs below 30 Mhz tend to get a little dicey with loss at higher frequencies. It's top rated freq is 450 Mhz (I must admit to being a little dubious, using SO-239s - they tend to get lossy at freqs that high). The 'N' version would be my choice in this case...

Mike

 

[Ed_Seedhouse]

The 7100 doesn't go below 25 Mhz, Ed...Mike

Well, I did check in advance but I missed that. In that case a long wire is pointless of course.

 

[Ed_Seedhouse]

Yes, although how well would be open to debate. I'm not sure how tall the center element on that discone is...

Re the MFJ-1704 - coax switches that work well on freqs below 30 Mhz tend to get a little dicey with loss at higher frequencies. It's top rated freq is 450 Mhz (I must admit to being a little dubious, using SO-239s - they tend to get lossy at freqs that high). The 'N' version would be my choice in this case...

If, as someone has pointed out in another message, your receiver doesn't go below 25 mhz then you don't really need a long wire and it won't work very well.

If your Discone antenna is not good enough at the lower end you might hang a half wave dipole but the main thing is to get your Discone up as high as possible.

Frequencies this high, especially above 100 MHZ are essentially line of site and what mainly determines what you can receive is height unless you are surrounded on all sided by mountains. In general, if you can see it, you can hear it. And if you can't you can't.

And our planet being more or less round, the higher your antenna is the further you can see, and therefore hear. Or if you are lucky and live on a high hill that helps a lot!

Essentially you need a very wide band antenna up as high as possible. A Discone antenna works well for that. You can get wide band antennas with high gain, but they tend to be pricy.

 

[shortride]

The top center element on the D3000N from the load up is 78.75cm.

 

[k3cfc]

Antenna tuners is a little misleading so I'll just call it an antenna matcher because I think that's what it really is isn't it? Using a long wire on an ICOM R7100 receiver, which antenna matcher would anyone recommend? I don't need to buy one with a meter because there will not be any TXing going on. With the wide band coverage of the R7100 wouldn't an antenna matcher just need a band selector and a tune knob? You just monitor the signal meter on the receiver while tuning correct?

Here is something i ran across thought you might be interested in.

http://websdr.ewi.utwente.nl:8901/