Antenna for cramped quarters

[N8MXL]

Hi all. I'm returning to the hobby after a 30+ year absence. I've forgotten a ton of radio theory, but I'm relearning it. When I got licensed as a 10-year-old I had access to my dad's multitude of antennas and his automatic tuner. All I have now is his Elecraft K2, a power supply, and a ladder-fed dipole. I live in a rented townhouse, so an outdoor antenna is out of the question. I thought about putting the dipole in the attic, but I live with my girlfriend and she's not keen on the idea of ladder line coming out of the ceiling. That means I'm very limited on what I can put up to get back on the air. So far I've considered:

• EFHW - I like that it can cover multiple bands without a tuner. I know they can be bent into weird shapes and still work passably, but I'm not sure if that extends to the kind of contortions required to fit one in a 10'x13' room. Ideally I'd want to build it for 40m so I also get 20, 15, and 10, but I can live with just 20 and 10 (which seems dead at the moment) for now. As I type this I'm getting ideas about putting the UNUN in the closet next to me and punching a tiny hole in the ceiling of the closet to run the radiating element up into the attic where nobody will see anything.
• Spiral loop - Takes up little space and can be put away when necessary, but is limited to a single band without a tuner.

The K2 is limited to 15W. As far as I can tell I won't be exposed to unsafe levels of RF at that power with the antenna in the same room as me.

Any suggestions? Money is on the tight side at the moment, so something I can build myself out of readily available components is ideal. Thank you!

 

[VK3RX]

I thought about putting the dipole in the attic, but I live with my girlfriend and she's not keen on the idea of ladder line coming out of the ceiling.

In one rental I had a trap dipole outside with a center balun and coaxial cable run under the roof tiles then down a wall cavity. The coax went to a AC mains socket, which originally included a Type F TV socket that I replaced with a SO239 socket.

So no drilling of holes, and easily undone when I left.

You may be able to do similar with a dipole or other type in your attic i.e. fed with coaxial cable rather than ladder line and a similar socket arrangement.

 

[popnokick]

You imply you can get into the attic. Unless there is foil insulation or excessive HVAC aluminum up there, it's a much better place for the EFHW or any other indoor antenna. And ditch the ladder line... it's not appropriate for indoor use. The EFHW is fed with coaxial cable, which you can still put through a small hole in the corner of the closet, and easily remove should that time come. Also, VK3RX's suggestion about using an existing wall plate is a good one. If you see cable TV or F-type antenna connectors on a wall plate there is a possibility that the entry point for the TV cable / antenna is in the attic. Look for it when you're in the attic. I found a complete CATV distribution network in my attic the led to wall plates in almost every room. Great for scanner antenna, but if you're going to transmit you'll need to replace the 75 own coax with 50 ohm. But at least you'll know there is a path for you to run the cable.

 

[k8niv]

A EFHW 4010 will work for u it don't take much room, one I have is 66ft long I think, and tunes well 40-10m, but with a external tuner, well I can get 60m and 80m with mine, maybe not work well on those bands but I talk on those bands here myself.....one I have came from ebay for 40 bucks.....been using it now about a year...

 

[N8MXL]

In one rental I had a trap dipole outside with a center balun and coaxial cable run under the roof tiles then down a wall cavity. The coax went to a AC mains socket, which originally included a Type F TV socket that I replaced with a SO239 socket.

So no drilling of holes, and easily undone when I left.

You may be able to do similar with a dipole or other type in your attic i.e. fed with coaxial cable rather than ladder line and a similar socket arrangement.

That gives me ideas for when we hopefully live in a standalone house where I can have an outdoor antenna. There is a cable outlet in this room, but it's on a wall that I don't think I can access from the attic to run a cable. I'm almost positive all that wiring goes downstairs and not up.

You imply you can get into the attic. Unless there is foil insulation or excessive HVAC aluminum up there, it's a much better place for the EFHW or any other indoor antenna. And ditch the ladder line... it's not appropriate for indoor use. The EFHW is fed with coaxial cable, which you can still put through a small hole in the corner of the closet, and easily remove should that time come. Also, VK3RX's suggestion about using an existing wall plate is a good one. If you see cable TV or F-type antenna connectors on a wall plate there is a possibility that the entry point for the TV cable / antenna is in the attic. Look for it when you're in the attic. I found a complete CATV distribution network in my attic the led to wall plates in almost every room. Great for scanner antenna, but if you're going to transmit you'll need to replace the 75 own coax with 50 ohm. But at least you'll know there is a path for you to run the cable.

I can get into the attic. I don't recall any annoying metal up there. All I saw was wood and fiberglass. This is a second floor bedroom and all the HVAC conduits are in the floor underneath it.

I was thinking to keep the UNUN in the closet and only make a hole small enough for the radiating wire to go through to minimize the damage I'll have to repair on the textured ceiling when we hopefully move out of here in the spring. Should I not to do it that way and run the coax all the way up to the attic instead?

A EFHW 4010 will work for u it don't take much room, one I have is 66ft long I think, and tunes well 40-10m, but with a external tuner, well I can get 60m and 80m with mine, maybe not work well on those bands but I talk on those bands here myself.....one I have came from ebay for 40 bucks.....been using it now about a year...

I was always a creature of 40, 20, and 10, so 80 isn't a big deal for me at this time. Maybe down the road when I have room for a bigger antenna.

On the subject of tuners, is the hype about EFHWs not needing one correct? I plan to eventually build a tuner (I always enjoy building rather than buying when practical), but if I can get away without one for now that would help a lot.

 

[prcguy]

Most EFHWs made for 40m on up will work ok without a tuner on 40, 20, 15 and 10m. The 80m version will do the same but 80m will resonate near 3.58Mhz in the CW portion of the band. MyAntennas makes one with a mod that resonates around 3.9MHz in the phone portion of the band and you can add that simple mode to most brands.

On the subject of tuners, is the hype about EFHWs not needing one correct? I plan to eventually build a tuner (I always enjoy building rather than buying when practical), but if I can get away without one for now that would help a lot.

 

[N8MXL]

It sounds like a 40m EFHW in the attic is the way to go. That will get me on the air affordably and within the aesthetic boundaries dictated by cohabitation. Thank you all for the advice!

 

[popnokick]

Run the coax all the way up into the attic and place the UNUN and radiating element (wire element) in the attic. Because the wire attached to the balun (unun) is the RF radiator you shouldn’t obstruct it by running it through the closet ceiling and attic floor.

 

[prcguy]

You can really mess up an end fed by taking a 64ft long 40-10m version and bending it where straight runs are less than 20ft long and make right angle turns, especially if they fold back on themselves. How much vertical height does your attic have? I think a good mobile HF screwdriver mounted in the middle of a large ground plane of chicken wire stapled to the attic floor can work very well. You don't really need that much height because instead of a 6ft or 9ft whip on top you can make a wire top hat suspended from the rafters that will equal or exceed the performance of a 9ft whip on top of the coil and you only need to go about 2ft above the coil with a capacity hat.

Something like a Tarheel 100HP or High Q screwdriver can be had used that will cover 80-10m for the Tarheel and 160-10m for the High Q. I get fantastic performance from mine on a vehicle and you can lay out way more ground plane in an attic compared to a vehicle and being elevated in an attic can also increase performance.

 

[k8niv]

N8MXL, the endfed 4010 I run, it hangs horizontal at 60ft off the ground, and it's a 110ft run of coax to the lightning arrestor before it comes in the shack, for the most part the swr is low but on 12m swr is higher, in which I also have a external tuner inline and use it when needed....u may hang one of these up in the attic, no telling what the swr would be there...

 

[N8MXL]

You can really mess up an end fed by taking a 64ft long 40-10m version and bending it where straight runs are less than 20ft long and make right angle turns, especially if they fold back on themselves. How much vertical height does your attic have? I think a good mobile HF screwdriver mounted in the middle of a large ground plane of chicken wire stapled to the attic floor can work very well. You don't really need that much height because instead of a 6ft or 9ft whip on top you can make a wire top hat suspended from the rafters that will equal or exceed the performance of a 9ft whip on top of the coil and you only need to go about 2ft above the coil with a capacity hat.

Something like a Tarheel 100HP or High Q screwdriver can be had used that will cover 80-10m for the Tarheel and 160-10m for the High Q. I get fantastic performance from mine on a vehicle and you can lay out way more ground plane in an attic compared to a vehicle and being elevated in an attic can also increase performance.

I'd guess it's at least 10 feet of vertical space. I'll be sure to avoid right angles in any shorter runs.

I looked into screwdriver antennas, which I'd never heard of until you mentioned them. They're out of my price range right now, but I'll keep them in mind for down the road when I need to fit into a small space again.

 

[mmckenna]

Be cautious with higher power radios in a townhouse. Usually there is a central fire alarm system that can be triggered by high RF, and having your antenna in the attic can put it closer to fire alarm wiring. Keep RF power low until you know for sure.
Good luck, I hope you find an antenna that not only works, but keeps your girlfriend happy.

 

[N8MXL]

N8MXL, the endfed 4010 I run, it hangs horizontal at 60ft off the ground, and it's a 110ft run of coax to the lightning arrestor before it comes in the shack, for the most part the swr is low but on 12m swr is higher, in which I also have a external tuner inline and use it when needed....u may hang one of these up in the attic, no telling what the swr would be there...

That's the plan. I've ordered the parts I need to build the antenna. I'll probably have to stay off 12m for now until I build/acquire a tuner.

 

[N8MXL]

Be cautious with higher power radios in a townhouse. Usually there is a central fire alarm system that can be triggered by high RF, and having your antenna in the attic can put it closer to fire alarm wiring. Keep RF power low until you know for sure.
Good luck, I hope you find an antenna that not only works, but keeps your girlfriend happy.

I didn't know that. The only radio I have maxes out at 15W. I was a fan of QRP growing up and plan to stick to low power for now anyway. I like the challenge of seeing how far I can reach on minimal power.

 

[N8MXL]

I forgot how many types of coax there are. I got myself a bit tied in knots trying to sort it all out, but I think I'm getting a handle on it. Is RG-8X appropriate for 15W maximum power and BNC connectors?

 

[prcguy]

RG-58 would be fine for a short to modest run and easier to deal with.

 

[N8MXL]

RG-58 would be fine for a short to modest run and easier to deal with.

Looks like it's also a little lighter than RG-8X, which I'd want if I ever carry through on my plan to take a rig up a mountain on a hiking trip and setup on a peak.

Does it matter if it's RG-58/58A/58B/58C? Do the slight variations in impedance and signal attenuation make any real-world difference?

 

[prcguy]

RG-58 has a solid copper center conductor, RG-58A/U has a stranded copper center conductor as does RG-58C/U but C is usually tinned copper center and braid. I would recommend A or C.

 

[N8MXL]

RG-58 has a solid copper center conductor, RG-58A/U has a stranded copper center conductor as does RG-58C/U but C is usually tinned copper center and braid. I would recommend A or C.

I found some RG-58A/U for a decent price. That's the last part I need to make a working antenna for receiving. Now I just need some sort of SWR indicator to get it tuned for transmit.

 

[popnokick]

If you don’t have the tuner option on your K2 then try the rig with no tuner first. Your antenna may be fine without a tuner. If you do get a tuner many of them will have SWR meters as part of the tuner. That will save you from having to buy a separate SWR meter. And the autotuners don’t really need one unless your SWR is off the charts (> 10 : 1). If you have some leftover $$ and want a comparatively inexpensive yet accurate antenna analyzer look at the Nano-VNA.