Build shortwave antenna

[btlacer]

Hi everyone, hope everyone is doing fine during this holiday season. I am here because I am trying to decide what type of antenna I need for shortwave. I am running one of those rtl sdr receivers and I am wanting to run a antenna for outside. I have room to put wire up in a tree. I have thought about a broomstick, longwire, random or end fed. I would like to be able to feed it with rg8x coax so it's going to have to have a so-239 connector. Anyone have any ideas of what to use? If I build a broomstick I already have a 10 foot pvc pipe that I can use and a mast it can be mounted on. Any help I would appreciate it!

 

[ko6jw_2]

The broomstick is a helically wound short vertical antenna. You would need an antenna tuner. Longwires technically are several wavelengths long, not just a "long" piece of wire. A random wire with a tuner might be the easiest. The key is aperture. You can make a short antenna radiate well for transmitting, but it captures less energy for receiving. The bigger the area the better. Don't forget a good earth ground. It will improve reception and lower noise.

 

[k1agh]

Whats a good tuner to use

 

[ka3jjz]

Whats a good tuner to use

Please don't hijack a thread - start a new one for asking different questions...but to begin, there are very few real antenna tuners on the market that a typical listener or ham can buy...

Oh I can hear it now - the loud screams of 'SAY WHAT'? Yep, it's true...

Real 'antenna tuners' are actually placed at the top of the feedline connected to the antenna.

A so-called antenna tuner - a transmatch might be somewhat more correct - that you see from MFJ, Palstar or several others does nothing more than provide a better resonant match of the antenna and feedline (yes, you read that right) for your receiver. This is an important concept - any kind of mismatch issues you might have on your antenna and feedline still exist there.

Many transmatch designs revolve around providing a 50 ohm feed to a transceiver. Because of this, many portables may not benefit much from such designs (altho you won't hurt the portable one bit by trying - and depending on what kind of load the antenna jack on your portable expects, it might work...). However, I do recall that a pi-network design was fairly popular many years ago for folks using portables. I'm sure that you can Google that if you're interested. They aren't hard to build and are another ideal 'first timer' type projects.

Transmatches are fine when you have a less-than-desirable situation for an antenna (and even some designs suggest one for best performance), but by and large, if you have a good outdoor antenna, properly fed, there's little need for a transmatch in a receive-only environment. For transmitting, tho, that's a horse of another color...

Mike

 

[ka3jjz]

Hi everyone, hope everyone is doing fine during this holiday season. I am here because I am trying to decide what type of antenna I need for shortwave. I am running one of those rtl sdr receivers and I am wanting to run a antenna for outside. I have room to put wire up in a tree. I have thought about a broomstick, longwire, random or end fed. I would like to be able to feed it with rg8x coax so it's going to have to have a so-239 connector. Anyone have any ideas of what to use? If I build a broomstick I already have a 10 foot pvc pipe that I can use and a mast it can be mounted on. Any help I would appreciate it!

How much room do you have outside? How many trees? Many folks start off with a PAR end fed, but that's far from the only thing you could use. Our HF Antennas wiki has several articles on different designs. And having only one antenna can actually limit you somewhat. You see, propagation can be very fickle - a signal might not come in well on one type of antenna, but may come in clearly on another antenna of a completely different type.

 

[IdleMonitor]

This is the one that I'm currently using. http://pages.ebay.com/link/?nav=item.view&id=321455435341&alt=web I have it about 6-7 ft off the ground with half of it between two buildings. Does the job just fine for general hf listening with a rtl sdr.

I have this feeding into a duplexer. This antenna for my below 30 mhz and I have a discone on the roof for everything above 25 mhz.

I'm hoping next summer to run the wire antenna from the corner of the house to the clothesline pole. It'll fit right in and no one will even notice it and should be about 20 ft off the ground.

 

[k1agh]

Sorry I didnt know that would be hijacking all I wanted him to do was expand on his answer.






QUOTE=ka3jjz;2301805]Please don't hijack a thread - start a new one for asking different questions...but to begin, there are very few real antenna tuners on the market that a typical listener or ham can buy...

Oh I can hear it now - the loud screams of 'SAY WHAT'? Yep, it's true...

Real 'antenna tuners' are actually placed at the top of the feedline connected to the antenna.

A so-called antenna tuner - a transmatch might be somewhat more correct - that you see from MFJ, Palstar or several others does nothing more than provide a better resonant match of the antenna and feedline (yes, you read that right) for your receiver. This is an important concept - any kind of mismatch issues you might have on your antenna and feedline still exist there.

Many transmatch designs revolve around providing a 50 ohm feed to a transceiver. Because of this, many portables may not benefit much from such designs (altho you won't hurt the portable one bit by trying - and depending on what kind of load the antenna jack on your portable expects, it might work...). However, I do recall that a pi-network design was fairly popular many years ago for folks using portables. I'm sure that you can Google that if you're interested. They aren't hard to build and are another ideal 'first timer' type projects.

Transmatches are fine when you have a less-than-desirable situation for an antenna (and even some designs suggest one for best performance), but by and large, if you have a good outdoor antenna, properly fed, there's little need for a transmatch in a receive-only environment. For transmitting, tho, that's a horse of another color...

Mike[/QUOTE]

 

[majoco]

Forget about the broomstick - it's only a small aperture and still needs a tuner to make the best of a bad job. You need to make a replica of the PAR Electronics EF-SWL Antenna - it costs around $75 but you can do it for much less than that. A wire out to your tree plus a 9:1 transformer will do you very well and maybe cost $20. DON'T feed a wire to your radio with coaxial cable alone without a transformer - most of your signal will be shunted to ground via the unmatched capacitance of the cable - match the antenna to the cable with the transformer and you'll have an ace antenna. DON'T connect a random wire to the whip antenna of your radio - the static sensitive devices at the front of the modern radios are liable to go bang.

 

[btlacer]

How do I make 9 to 1 transformer? I have lots of trees, well really three trees at the edge which are really tall. I was looking at the par swl antenna. I really don't have the money right now to buy a tuner so I will have to go without for now. Are there plans to build one like it? Thanks for all the feed back.

 

[ka3jjz]

Forget about needing a tuner. If you are going to put up a good outdoor antenna, chances are you won't really need one.

I haven't done this (yet), but I understand you can rescue the toroid (it's a doughnut-shaped coil form) from old PC power supplies. Then you need some magnet wire and a hot glue gun to hold your wiring in place.

The Shortwave SWL Antenna Yahoo group has quite a bit on this subject - read up on anything in their files section by John Doty or the late John Bryant. Mike

 

[Ed_Seedhouse]

A so-called antenna tuner - a transmatch might be somewhat more correct - that you see from MFJ, Palstar or several others does nothing more than provide a better resonant match of the antenna and feedline (yes, you read that right) for your receiver. This is an important concept - any kind of mismatch issues you might have on your antenna and feedline still exist there.

This is, actually, not true. See http://w5dxp.com/OWT1.htm which explains why.

Tuners are, however, really beside the point for receivers. Any decently long wire will pull in plenty of signal for a modern high sensitivity receiver to "hear". Actually you will often hear better on frequencies where your antenna is not resonant. An antenna at resonance amplifies all signals, including noise. And on receive it's noise that is usually the problem, not signal strength.

 

[Ed_Seedhouse]

I've tried the 9 to one transformers. And the tuners. And the pre-amps,

And yes, they make signals on some bands stronger. But guess what they also make stronger - noise!!

And it's noise that is the biggest problem in H.F. reception.

Get a decent length of wire up as high as you can and as far away from local noise as you can. Bring the signal into the house with coax cable, 50 or 75 ohm makes next to no difference. Ground the coax shield to a ground rod outside to shunt common mode current to ground and keep the noise level down. Or place a counterpoise the same length as the antenna wire on the ground, connected to the coax shield.

Then enjoy.