Interested in setting up a Discone Antenna

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Radioflow

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Hey RR users, I've been playing with SDR, And it's really a lot of fun, and a great entrance to the Radio world. I'm wanting to set up a Discone Antenna for general listening, I'd obviously want this on my Roof.

I don't come from any engineering or electrical backgrounds, However I know the basics of electronics and Radio. What parts would I require? What tools? How long does it take to set up generally, and how can I use multiple RECEIVERS (caps because I know TX isn't possible like this) with my single discone? What kind of Coax cables would make a good fit for me? And any additional hardware. My budget is a little limited for the time being, I would want to spend as little money as possible, while getting good hardware, ($100-150?) Max budget would probably be about $250. I'm interested in using up to 4 receivers, I have two now, And I plan to get more (RTL SDR's).

I would greatly appreciate help with this, Since I basically have no idea of what I'm doing. However! An important note is that my house is on the end of a small hill, so around 50 feet lower than the rest of the NORTHERN area. I also have a one story house, and the neighbor behind me (the only one(behind me)) has a two story house, I would assume that I'd need to be slightly taller than their house for best (in reason) signal quality?

Edit (important): Assuming I could put the antenna around the middle of my house (peak of the house), i'd need around 50-75 feet of cable. I could run this under the eave and through the wall outside of my room that I want to feed the cable in to.

Thanks everyone.
 
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n0nhp

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You will probably get as many recommendations as people answering your post, here's mine ;-)

Antenna height will make a difference on line of sight comms. A house in the way will be minimal disruption. Getting the antenna as far above your own house as possible is good for reducing noise from your own house and extending line of sight to the horizon. Be practical. A tripod roof mount with 20' of mast is usually on the edge of practical so you don't need additional guys and bracing of the roof.

For my RX only discone antennas I run RG6 75ohm coax. Don't worry about the "impedance mismatch". Broadband antennas and receivers do not have a constant impedance across the spectrum and any slight mismatch of coax is going to be negligible. It will also be about the cheapest, lowest loss cable you can get right now and is available off the spool at any big-box hardware store. Of course you will have to buy adapters for antenna and receivers.

Using the TV coax has another advantage. They are getting harder to find but the old analog TV amplified splitters cover 70MHz to 800MHz and I have had them work well to feed multiple receivers. If you are interested in higher frequencies a good high end passive cable TV splitter and amplifiers for your given interest area may be the way to go.

Good luck and have fun with it. There is no exact science to putting up antennas and half the fun is figuring out what you need and want for your situation (why do I have 8 antennas on my roof?)..


Bruce
 

Ubbe

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It would help with some pictures of your house. If you don't have a chimney to mount a mast to I would think it would be much easier to use a standard tv antenna mount that attach to the side of the house.

Amplifier and 1-4 catv splitter with RG6 coax with F connectors all around are perfect in your situation and suitable adapter for antenna and SMA RG174 cables with F adaptors for the SDRs.

/Ubbe
 

ko6jw_2

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You don't tell us what frequencies you want to cover. Diamond D130NJ is a great discone. These are tricky antennas to build yourself. ARRL antenna manual has designs. I have almost 50 years of experience and I wouldn't try to build my own.

You can build discones for any frequency. They have about a 10:1 ratio when properly designed.

The Diamond antenna is good from about 100- 1200 Mhz. They do not cover down to 25Mhz as advertised. Out of the box they tune up at 50Mhz. You can cover lower frequencies with a longer whip. However, the actual discone operates above 100Mhz. The rest is just a base loaded ground plane.

Use 50 ohm coax. Get the good stuff. The Diamond is a 50 ohm antenna and contrary to other comments is almost a constant impedance from 100Mhz to 512Mhz (my upper limit) when terminated properly and fed with N connectors.

If you must use RG-6 then don't buy it at home supply stores. Order high quality cable from HRO or DX Engineering. People will tell you that RG-6 has lower loss than RG-8X, but all specs assume a constant impedance. I wouldn't use RG-8X either. F connectors and UHF connectors are not constant impedance either. That's why I use N connectors. My antenna analyzer proves there is a major difference.
 

Radioflow

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Here's an image with some drawing from google earth, This should show what I want to do. I'm also wanting to target the 400MHz range, Since my city's trunking is 482* MHz, But as much coverage as possible would be great, I'm also interested in ADS-B, What about that?
Thanks guys.


Edit: Here is a much easier to see image.
 

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Ubbe

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That unused satelite dish probably have an unused RG6 coax already going to a room in the house?
There must be loft space under the roof where you could reach the coax and cut it and attach to a new RG6 that you somehow could manage to get thru the ceiling to your room.

The satelite mount could be inforced to carry the discone and for the ADS-B antenna you make that yourself from 4 pieces of RG6 cable and put in a plastic tube.

There are combiners for $20 that let you use a tv antenna together with a satelite dish using the same coax. One input of the combiner are up to 900MHz and the other above 900MHz. I 've measured a combiner to 0.1dB attenuation in the passband. At the other end of the coax you use the same combiner to split the signals again.

With that CATV 1-4 splitter you have one output that is power pass and you program the RTL-SDR to output 5V and then have an amplifier in the loft. Or you could get a 1-6 splitter and use the power pass for a 12v power source and use a standard $10 in-line sat amplifier.

/Ubbe
 

popnokick

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Agree completely with Ubbe - you need to investigate what can be done with the coax from the unused satellite dish. When I moved in to my house there was an abandoned satellite TV system that had been converted from a CATV system. There was a dish on the roof and a multi-output splitter in the basement with RG-6 running to many rooms in the house. I disconnected the satellite splitter,/coupler put an antenna in the attic (would prefer rooftop, but the satellite location was too low and the high point of the roof is too near power lines) and put a new splitter in the attic. I now have one antenna in the attic feeding three scanners and one weather radio in four different rooms of the house.... and I didn't have to install any coax at all. If you're not sure what goes where with the abandoned coax in the house, get yourself a TV cable coax tracing tool. They're inexpensive and readily available and allow you to identify where a given length of coax goes to / from (once you locate the splitter / multi coupler).
 

Radioflow

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If you look at the bottom left, there is a newly abandon satellite, how good would that make for a position?
 

Ubbe

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Yes, you can use that with a mast that makes the dipole and ADS-B antenna reach at least above your own house roof, preferable also over your neighbours.

/Ubbe
 
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