Shortwave Longwire Antenna?

[kyle_in_rure]

Hello, new member here. I recently discovered Shortwave radio, and have made a habit out of listening frequently. I am using the Tecsun PL-600 portable right now.

I have about 60-70 ft of #14 insulated wire strung across the yard, which I was using for an AM crystal radio set I built a while ago. The wire transitions to about 8 ft. of RG6 coax via a soldered connection in a plastic bottle outside. I thought about trying to use it with my radio, which uses a headphone jack as an external antenna adapter. I bought a headphone plug and connected it to the antenna with an alligator clip. Wow! I was able to pick up much more than I could with the radio's telescoping antenna alone. I even picked up WWV and WWVH (the time signal stations) at the same time.

Here is my ultimate question, I would like to run the antenna wire inside. I thought about doing a similar setup like my TV antenna is now: about 30 ft of coax outside, through a window via a flat coaxial cable (NOT twinlead, they sell them at RadioShack). However, will I lose a lot of signal through 30-40 feet of coax? Also, what do I do about grounding? Right now I have the coax shield just cut off, it is not connected. I could always run it through a grounding block like my TV antenna is. I wonder about signal loss here, as well, however.

Thanks in advance for any information.

 

[ka3jjz]

Moved to the receive antennas forum....

Inside connections are always worse than putting it outdoors. You seem to have some success with your current setup - I'd say don't mess with success. Indoors, any wire antenna like you have described will pick up just about every noise source in your home, along with whatever signal you really want to hear.

If you want to do something more, put up a 2nd antenna like the one you have, but in a different direction. For example if your current wire is running N-S, put one up going E-W. You can really never tell if propagation would favor the 2nd antenna over the first (it's certainly possible, depending on many factors), but it wouldn't hurt anything to try it.

Mike

 

[n5ims]

The lower in frequency you get (shortwave is quite low in frequency, the AM broadcast band is even lower) the less loss per foot you'll get from your coax. Unless you use some very bad coax, you'll never notice the loss over that 30 - 40 foot run.

To help illustrate what I said, I ran some numbers for you. Using some Tandy RG-58 (commonly used, but not very good loss numbers) on a typical scanner run (50 feet on the 800 MHz band) you'll end up with 7.2 dB loss. To get that same loss at 25 MHz your coax run would need to be about 375 feet long.

Using some much better coax (LMR-400) over that same run (50 feet run on the 800 MHz band) you'll end up with only about 1.9 dB of loss (much better!). With that same coax at 25 MHz you'd now need to go through about 325 feet to match that loss.

To show you just how much that extra coax would hurt you, I also ran those numbers. For your current 8' run of RG-6, you have about 0.108 dB of loss. Moving to the worst-case 40' run of RG-6 you'll have about 0.542 dB of loss. Scanner folks would kill to only have half of a dB loss in their coax! For you to actually hear a difference between those two runs (assuming everything else remains the same) is that distant SW station would need to drop their 100,000 watt signal down to about 1,000 watts. Even then you'd probably still hear them quite well.

 

[kyle_in_rure]

Moved to the receive antennas forum....

Inside connections are always worse than putting it outdoors. You seem to have some success with your current setup - I'd say don't mess with success. Indoors, any wire antenna like you have described will pick up just about every noise source in your home, along with whatever signal you really want to hear.

If you want to do something more, put up a 2nd antenna like the one you have, but in a different direction. For example if your current wire is running N-S, put one up going E-W. You can really never tell if propagation would favor the 2nd antenna over the first (it's certainly possible, depending on many factors), but it wouldn't hurt anything to try it.

Mike

Wow, and I thought I had the right forum.....thanks for fixing that.

I wasn't trying to make an indoor antenna, just run coax inside so I could use the radio inside. The antenna wire actually runs N-S, attaches to a post, and then runs East to West. So I should be covered there.

Thanks

 

[kyle_in_rure]

The lower in frequency you get (shortwave is quite low in frequency, the AM broadcast band is even lower) the less loss per foot you'll get from your coax. Unless you use some very bad coax, you'll never notice the loss over that 30 - 40 foot run.

To help illustrate what I said, I ran some numbers for you. Using some Tandy RG-58 (commonly used, but not very good loss numbers) on a typical scanner run (50 feet on the 800 MHz band) you'll end up with 7.2 dB loss. To get that same loss at 25 MHz your coax run would need to be about 375 feet long.

Using some much better coax (LMR-400) over that same run (50 feet run on the 800 MHz band) you'll end up with only about 1.9 dB of loss (much better!). With that same coax at 25 MHz you'd now need to go through about 325 feet to match that loss.

To show you just how much that extra coax would hurt you, I also ran those numbers. For your current 8' run of RG-6, you have about 0.108 dB of loss. Moving to the worst-case 40' run of RG-6 you'll have about 0.542 dB of loss. Scanner folks would kill to only have half of a dB loss in their coax! For you to actually hear a difference between those two runs (assuming everything else remains the same) is that distant SW station would need to drop their 100,000 watt signal down to about 1,000 watts. Even then you'd probably still hear them quite well.

Wow, didn't know that. Thanks for that info. My biggest concern was signal loss at junction points. Currently I have about 6 ft. of coax coming down the pole, which I will either run into a coax-junction (whatever you call it) or a grounding block, then another few feet to the flat coax cable in the window (this thing here: RadioShack 8 Flat Coaxial Cable : Coaxial Cables | RadioShack.com), then a length of coax inside the house, to the headphone adapter. I know with TV signals you lose a lot at connections, not sure if that would be the case here. I will have to try it out.

Also, what do you think about grounding? Should I run it through a grounding block, like I have my TV antenna? Not sure how I would hook that up with the headphone adapter....

Thanks

 

[kyle_in_rure]

***I found an adapter online that changes coax to headphone jack, so I may order that instead of fighting with the direct-wire headphone jack I bought at Radio Shack.

By the way, in terms of reception, I am in the South-central US if that makes a difference.

 

[Boombox]

Re: Grounding: You'll get different responses from different SWL's. A lot of them believe grounding helps reception, others (like myself) never noticed much of a difference. I don't use the ground with any of my radios.

I would definitely keep a ground handy for safety purposes -- to ground the antenna when it's not in use. If I recall, in the SE US there is a lot of lightning storm activity (a lot more than we have in the coastal NW US). If your grounding block has lightning protection built in, it would probably be a good idea to use one.

 

[kyle_in_rure]

Re: Grounding: You'll get different responses from different SWL's. A lot of them believe grounding helps reception, others (like myself) never noticed much of a difference. I don't use the ground with any of my radios.

I would definitely keep a ground handy for safety purposes -- to ground the antenna when it's not in use. If I recall, in the SE US there is a lot of lightning storm activity (a lot more than we have in the coastal NW US). If your grounding block has lightning protection built in, it would probably be a good idea to use one.

Yeah, we do have a lot of thunderstorms. I usually go outside beforehand and disconnect everything before we have a storm. I may go ahead and ground the coax just for my own satisfaction; the grounding block is connected to an 8 ft. ground rod.