A few questions

Hello everyone, I have a RTL SDR dongle and a Ham-It-Up upconverter. It works great. I've tested it out hooked up to an Antron 99 and it receives fairly well. However, I know that this isn't the best antenna to use for this purpose since it's vertically polarized.

I'd like to use a longwire antenna but I don't really know how to connect it. In the past, with other shortwave receivers, I just hook the longwire directly to the telescoping antenna on the receiver itself.

If I put a longwire antenna in my attic. How do I go about connecting it to my upconverter? I've tried connecting a longwire to the center conductor of a piece of coax and then connecting this to the upconverter but this didn't work very well at all. What about the outer conductor/shield? What do I do with it? If I ground it, what do I ground it to since everything is inside the house?

I'm just a bit confused.

Also, are there any other antennas that will be a better choice than a longwire for SWL? I'm putting it in the attic and I have a large amount of space to work with.

Don't dis verticals, they can be very good performers. For a wire, I'd go with a 9:1 balun fed with coax.

[I'm a moron] disregard, wrong post.

It's not really a longwire if you can get it in your attic - a true longwire is at least 1½ wavelengths long at your lowest desired frequency so if you want to listen to the Hams on 80metres.....120 metres/133yards!
A dipole is alright if you want to listen to a specific frequency and it's harmonics, but for all SW bands you want something untuned - try an OCFD - an 'off centre fed dipole' also known as a Carolina Windom. It's like a dipole but one leg is twice as long as the other. So if you have 100feet to play with, one leg can be 66ft and the other 33ft - a 9:1 unun (often called a balun but it's not balanced) to 75 ohm coax in the middle and you're set. Get a proper adaptor for your dongle to take a BNC or PL259 connector.

An OCFD is a tuned antenna and works best on harmonically related frequencies based on its lower design frequency. Outside their resonant frequencies they degrade similar to a tuned dipole. They also use a 4:1 balun for most installations and sometimes a 6:1 is better if the antenna is 1/2 wave or higher above ground. I'm using a 40m OCFD as I type this at a remote facility in NE Canada listening to some HF chatter.

If the OP decides a dipole is the way to go then a random length center fed using a balanced feed line like TV twinlead or 450 ohm ladder line to a 1:1 choke balun at the radio works well. Most any dipole will have its sweet spots and bad spots across the spectrum unless you go with a more complicated T2FD like the B&W BWDS series.

I think an end fed wire with 9:1 balun is an easy to deal with antenna and cheap to make. The PAR end fed SW version is basically that and they work well.
prcguy

majoco said:

It's not really a longwire if you can get it in your attic - a true longwire is at least 1½ wavelengths long at your lowest desired frequency so if you want to listen to the Hams on 80metres.....120 metres/133yards!
A dipole is alright if you want to listen to a specific frequency and it's harmonics, but for all SW bands you want something untuned - try an OCFD - an 'off centre fed dipole' also known as a Carolina Windom. It's like a dipole but one leg is twice as long as the other. So if you have 100feet to play with, one leg can be 66ft and the other 33ft - a 9:1 unun (often called a balun but it's not balanced) to 75 ohm coax in the middle and you're set. Get a proper adaptor for your dongle to take a BNC or PL259 connector.

Click to expand...

I would never directly connect a PL259 via an adapter to that tiny antenna jack. Too much stress and that jack will eventually break.

Better to use a coax jumper with the proper jacks on either end. If the jumper breaks at least the dongle is still intact

Mike

Thanks for the info.

Although I have to ask, are there any antenna designs that don't require any sort of balun or unun? I don't have any toroidal cores on hand so I'd have to order some.

Don't over think it. Have you tried using a random length hunk of wire and simply connected it to your receiver antenna jack?

k9rzz said:

Don't over think it. Have you tried using a random length hunk of wire and simply connected it to your receiver antenna jack?

Click to expand...

I'm trying that now, just not in the attic. In my original post I said it didn't work very well but I tinkered with it some more over the past few days and got it working pretty well.

I just ran the wire to the center conductor of a PL-259 and then connected that to my upconverter.

I can receive from roughly 1mhz to 12mhz very well at night, but during the day I can't really hear much of anything from 14 to 30mhz. Although I'm not sure if that's something to do with my antenna or if those bands are just dead right now.

I'm also not sure how well a longwire would work in an attic. I'm guessing I'll have to build something with a balun. Just seems like a hassle compared to the construction of a longwire.

14 - 30 mhz propagation can vary widely from day to day. I usually check WWV on 15, 20, and 25mhz as well as CB at 27. If there's action on CB then I go up to 10 meters and if 10 sounds good, I try 6. Glad it's working!