Attic antenna recommendations

[Shark_Cage]

Looking to put a receive only antenna in my attic , good winter project. My reviewer's can hear from 160 through 10m. I have about a 35` open space to work with. Thinking of a folded dipole but I am so green I need some advice.

Thanks, Jim

 

[cockpitbob]

Attics are OK. I have a 2m/70cm Jpole and 10m/6m coupled resonator dipole in my attic. They work well enough and keep the wife happy.

My best advice is read about SLW antennas (short wave listening).
Remember, SWL antennas are identical to Tx/Rx antennas except they don't have to handle a lot of power and the associated high voltage. If either type of antenna has a really high SWR it will be fairly deaf.
Tx/Rx antennas also must provide a low SWR (less than 2:1), not because they are different than Rx-only antennas, but because lots of power reflecting back into a transmitter will fry it.

If you think you might be transmitting some day, what I would do is put up a Tx/Rx antenna with a tuner. Since (I assume) you want lots of bands, I would put up a dipole cut to not be resonant on any ham bands, add a balun to convert the balanced dipole to in-balanced for the coax going to the radio. 41' is a good choice for your available space. Then use a tuner. With a tuner you can make any antenna your bitch and force a tune on whatever band you want to use.

For my multi-band non-resonant antenna and 100W rig, I use this MFJ-941 Versa-Tuner manual tuner. Just tune for maximum loudness and write down the knob settings, or you could borrow an antenna analyzer to determine the knob settings.

 

[1776]

Not sure about SW, but I upgraded my TV attic antenna's before the over the air digital switchover happened in 2009. Since I'm in the Foxboro area between Boston and Providence I installed two, one 14' pointed to the center of the Boston transmitter towers and one towards Providence, with a signal combiner and amp for my in the wall cable distribution to every room. I got all the parts (Winegard HD7698P Platinum HD Series Antenna) and recommendations from U-DO-IT in Needham. When I tried FIOS TV four years ago the installer remarked how clear and beautiful the TV reception was when I informed him that the TV input setting was still on antenna. When I switched it over to FIOS it was not as good, the installer didn't say another word. I cancelled the FIOS TV part of the contract after the first year.

 

[Shark_Cage]

Attics are OK. I have a 2m/70cm Jpole and 10m/6m coupled resonator dipole in my attic. They work well enough and keep the wife happy.

My best advice is read about SLW antennas (short wave listening).
Remember, SWL antennas are identical to Tx/Rx antennas except they don't have to handle a lot of power and the associated high voltage. If either type of antenna has a really high SWR it will be fairly deaf.
Tx/Rx antennas also must provide a low SWR (less than 2:1), not because they are different than Rx-only antennas, but because lots of power reflecting back into a transmitter will fry it.

If you think you might be transmitting some day, what I would do is put up a Tx/Rx antenna with a tuner. Since (I assume) you want lots of bands, I would put up a dipole cut to not be resonant on any ham bands, add a balun to convert the balanced dipole to in-balanced for the coax going to the radio. 41' is a good choice for your available space. Then use a tuner. With a tuner you can make any antenna your bitch and force a tune on whatever band you want to use.

For my multi-band non-resonant antenna and 100W rig, I use this MFJ-941 Versa-Tuner manual tuner. Just tune for maximum loudness and write down the knob settings, or you could borrow an antenna analyzer to determine the knob settings.

One question (dumb) is 41' each side of the dipole?

Thanks,
Jim

 

[cockpitbob]

::

One question (dumb) is 41' each side of the dipole?

Thanks,
Jim

20.5' per side, but the length isn't hyper-critical. Normally you want an antenna's length to be 1/2 wave (1/4 wave per side), but it will only work well at that one resonant frequency. For an "almost all band" tuner fed antenna, you want to avoid resonant lengths where the total length = 1/2wave at whatever frequency you're operating at. The length isn't critical and I'm about to recommend one with 44' of wire.

After thinking about it, if you're considering a tuner and eventually upgrading to transmitting, I would put up an end-fed antenna fed by a 9:1 unun (and a tuner). End fed antennas are the same as di-poles except you feed them at the end instead of the middle. The real difference is the middle of an antenna presents a low impedance (close to 50 Ohms for a 1/2wave dipole) while the end fed presents a higher impedance which is why you use a 9:1 unun to divide the antenna's impedance by 9.

You can buy a pre-made one like this 1,000W, 80m - 6m one with 44' of wire. (myantennas.com is a good company.) Or you can make your own unun and use whatever wire you want (wire is wire). This kit claims 100W which sounds a bit high to me, but for $18 it's a cheap way to try end-feds. Here's a good article and instructions on rolling your own. There's no magic in these 9:1 ununs. They are all simply a transformer with a 3:1 turns ration (impedance change = turns ratio squared). The bigger the donut the more power and lower frequency it can handle. You can spend over $100 on one, but mainly you are paying extra for a better box and connectors.

 

[Shark_Cage]

::
20.5' per side, but the length isn't hyper-critical. Normally you want an antenna's length to be 1/2 wave (1/4 wave per side), but it will only work well at that one resonant frequency. For an "almost all band" tuner fed antenna, you want to avoid resonant lengths where the total length = 1/2wave at whatever frequency you're operating at. The length isn't critical and I'm about to recommend one with 44' of wire.

After thinking about it, if you're considering a tuner and eventually upgrading to transmitting, I would put up an end-fed antenna fed by a 9:1 unun (and a tuner). End fed antennas are the same as di-poles except you feed them at the end instead of the middle. The real difference is the middle of an antenna presents a low impedance (close to 50 Ohms for a 1/2wave dipole) while the end fed presents a higher impedance which is why you use a 9:1 unun to divide the antenna's impedance by 9.

You can buy a pre-made one like this 1,000W, 80m - 6m one with 44' of wire. (myantennas.com is a good company.) Or you can make your own unun and use whatever wire you want (wire is wire). This kit claims 100W which sounds a bit high to me, but for $18 it's a cheap way to try end-feds. Here's a good article and instructions on rolling your own. There's no magic in these 9:1 ununs. They are all simply a transformer with a 3:1 turns ration (impedance change = turns ratio squared). The bigger the donut the more power and lower frequency it can handle. You can spend over $100 on one, but mainly you are paying extra for a better box and connectors.

Hi, I did take your advice and I purchased the antenna you recommend. I installed it in my attic but I have one concern. To fit it in I had to install it like an L in my attic. 90 deg turn about halfway down the wire. What is your opinion?

On a side note I passed my General today.

 

[cockpitbob]

First, contrats on the upgrade!!!

If you're using a tuner then it will work fine with the bend in it. There's no way to easily predict what the bend will do, but heck, it's an attic antenna which is a compromise anyway, so you get what you get. For all we know it will make it better on your favorite band.

The bend will lower the resonant frequency of the antenna some. Being in the attic instead of free air will also lower its resonant frequency some. If it's lowered enough that it resonates in the middle of one of the ham bands then the tuner might not be able to get a good tune on that band. In that case, trim 6" off and see if that fixes the problem. If not, try another 6" and maybe do that 2 more times for a total of 2'. If you still have a band you can't get a match on, there may be something else up.

 

[Uzi2]

What are the rectagular dimensions of your attic space at floor level?

You could make a loop antenna and use a small tuner for receiving. Loops are quiet (better signal to noise ratio) and broadbanded.
Some #14 THHN wire tacked up with insulated romex staples. Feed it with either ladder line or coax to a cheap tuner and it should hear well.

Congrats on passing your general exam!

 

[cockpitbob]

BTW, I hope your house and neighborhood is quiet. After several hours of trying I haven't tracked down why my house now creates S8-S9 noise on all bands from 80meters to 15. I just got back from a weeks vacation in a rented lake-side house in NH that generated S9 +20bB noise. I tracked it down to the DSL box. I gave up on operating that week. There's no way the 13 relatives with us were going to put up with me turning off their WiFi for 2 or 3 hours a day. I put the FT-857 back in the car and did a little mobile operating.

When I got home I drove around town doing an informal survey and found areas with no background noise and some areas only 1/4mile long with S8+ noise. It seemed like 1 house was causing it in those little stretches of noise. Some LED lights, plasma TVs and some cheap florescent lights are killing the hobby.

 

[DispositionMatrix]

Looking to put a receive only antenna in my attic , good winter project. My reviewer's can hear from 160 through 10m. I have about a 35` open space to work with. Thinking of a folded dipole but I am so green I need some advice.

Thanks, Jim

You can get a 20m folded dipole in that space, but you cannot do a fan configuration. You could add folded 10 and 6 dipoles perpendicular to the 20 as inverted Vs on separate cables. An EFHW 80-10 outside 130ft to a tree will take care of much of HF for you. It can be practically invisible.

 

[Shark_Cage]

I get the attic dimensions tomorrow. Right now I'm working on grounding and bonding.

Ok, another crazy question. Would a yagi be effective below the tree line? Ths is more a long term goal but I have some high trees at home and I don't know if I could afford a tower high enough to get above them let alone the wife factor lol.