Antenna for cramped quarters

[N8MXL]

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.

The K2's manual says it will survive transmitting into a high SWR, so I'm not super concerned about a perfect antenna match. I just want to make sure I haven't made some huge measurement or geometry error that's eating all my signal. In a continuing theme of build-not-buy I was thinking of building a simple LED-based SWR bridge that I could incorporate into a tuner down the road. That would get me a working meter for under $20. I've also looked at the ATU-100 kit, which would give me an SWR meter and autotuner for $40 in a small lightweight package (in case I carry through on my threat to lug a station up a nearby mountain for some SOTA). The NanoVNA is less expensive than I expected such a device to be, and it would be more comprehensive in its function, so I may be able to justify spending the money for one.

 

[merlin]

One of my best performers was a T2FD in a slopper configuration and ladder into the shack.
A buddy that lives in a HOA showed me his radical version of the same. I never saw it til he pointed it out.
Basically more a butterfly antenna, but he had some outstanding performance with it.
A pix is worth a thousand words >
Power handling is up to the termination resistor (non inductive)
You will need a 16:1 ballun, also power rated. You can see roof shape is not critical and a wee bit of gain toward the terminator.
Quite broadband, good SWR across the bands.
This is my work in progress where I live and the landlord is not keen on an antenna farm.

 

[merlin]

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 have found CW, FSK, FM, and other modes not much problem. SSB though, at 250 watt PEP, I have triggered a couple alarms including car alarms in the parking lot. 600 watt, and probably the case.

 

[mmckenna]

I have found CW, FSK, FM, and other modes not much problem. SSB though, at 250 watt PEP, I have triggered a couple alarms including car alarms in the parking lot. 600 watt, and probably the case.

We took over a site where a 4 watt UHF hand held would get into the main HV breaker for the site and knock all the power off line. Issue was obviously limited to the high voltage techs and only when talking on the radio. Solution was to have someone standing outside the room with a radio while the HV tech did his thing.

Since I no longer use UHF at work, I pulled the sign down and have it hanging in my garage.

 

[N8MXL]

One of my best performers was a T2FD in a slopper configuration and ladder into the shack.
A buddy that lives in a HOA showed me his radical version of the same. I never saw it til he pointed it out.
Basically more a butterfly antenna, but he had some outstanding performance with it.
A pix is worth a thousand words >
Power handling is up to the termination resistor (non inductive)
You will need a 16:1 ballun, also power rated. You can see roof shape is not critical and a wee bit of gain toward the terminator.
Quite broadband, good SWR across the bands.
This is my work in progress where I live and the landlord is not keen on an antenna farm.

I considered a setup like this, but there's no clean way to get the feed line out there. I live in a multi-unit building. My neighbors would probably notice me putting a wire under their roof and not be amused. When I hopefully live in a house again this could definitely be a good way to go.

 

[mmckenna]

My neighbors would probably notice me putting a wire under their roof and not be amused.

Dude, Christmas lights. 'Tis the season….

 

[merlin]

Nosey neighbors are easy to pathefy by telling them you are cleaning and maintaining the rain gutters. The feed line can be painted to match the building, then out of sight- out of mind.
What I have now for feed line is LMR600 in a brilliant shade of yellow. I only use it because I have a few 200 foot lengths of it.
From my discone, lays across the roof then down to a window and nobody notices it.

 

[merlin]

We took over a site where a 4 watt UHF hand held would get into the main HV breaker for the site and knock all the power off line. Issue was obviously limited to the high voltage techs and only when talking on the radio. Solution was to have someone standing outside the room with a radio while the HV tech did his thing.

Since I no longer use UHF at work, I pulled the sign down and have it hanging in my garage.

Wow, 4 watts ? I believe it is time to rethink your power service. And to a radio site no less.

 

[mmckenna]

Wow, 4 watts ? I believe it is time to rethink your power service. And to a radio site no less.

It's not the radio. This was years and years ago, Motorola's, before we took over the site.
It's not the power service. Electric utility was fine. This was internal high voltage distribution stuff for an old wafer fabrication facility
It was the sensors in the HV breakers. Not my circus, not my monkeys. Radios were working fine.

RF can get into systems and cause undesired performance. I've been to sites where using a radio in the wrong place gets into the fire alarm system. It's addressed in FCC Part 15: Move the two devices further apart if undesired operation occurs.

No matter what, if you are the last guy to show up and everything worked fine before, guess who's problem it is? Running high RF levels in an attic of a shared building is less than ideal.

 

[popnokick]

Just so we don't lose sight of the facts... in the original post that started this thread (and at least one that followed) the OP wrote:

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...

 

[N8MXL]

Nosey neighbors are easy to pathefy by telling them you are cleaning and maintaining the rain gutters.

The neighbors may fall for that, but sadly the maintenance people who are constantly out fixing stuff (some of who also live here) would not. Yesterday I watched two of them have an hour-long conversation about who-knows-what while staring at the air conditioner next to my patio.

 

[N8MXL]

Just so we don't lose sight of the facts... in the original post that started this thread (and at least one that followed) the OP wrote:

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...

Yeah, after reading about 4W causing so much havoc I'm less confident that my first transmission won't open a portal to another dimension. We have a neighbor who's so sensitive to the slightest disturbance in the universe (a few nights ago she banged on the wall and yelled at me for, as far as I can tell, existing) that I won't be surprised if she complains she's picking up CW from me on her fillings.

 

[N8MXL]

Running high RF levels in an attic of a shared building is less than ideal.

Living here in general is less than ideal, which is why we hope to find a house at a reasonable price in the spring. In the meantime I'm going to make good use of the power knob on the K2 and see what I can accomplish with only a few watts.

 

[mmckenna]

Living here in general is less than ideal, which is why we hope to find a house at a reasonable price in the spring. In the meantime I'm going to make good use of the power knob on the K2 and see what I can accomplish with only a few watts.

Yeah, I remember those days. Not ideal combination with a hobby like this.

Good luck on finding a new home.

 

[kk4obi]

This is a small consideration but before you mount a 40-10 end fed antenna put some marks at 1/2, 1/3 and 1/4 of the total length. These show you where the current nodes occur for 20, 15 and 10 meter operation. Try to make your bends at one or more of these points to get the more effective radiation pattern of full half wave(s) at whatever harmonic you want to use. The wire radiates as four half waves end-to-end when operating on 20 meters.

Use non-metal stand-offs to keep the antenna away from wood or anything that can adsorb your RF. How you route the antenna will likely cause some change in the harmonics from the usual straight design. If you feel the need to do tuning remember that any change in one band changes all the other bands too. To lower frequency cautiously use a small telescoping antenna attached at the wire-transformer junction. To raise frequency push a small loop of the antenna thru a small toroid to choke off that loop-length of wire.

 

[N8MXL]

This is a small consideration but before you mount a 40-10 end fed antenna put some marks at 1/2, 1/3 and 1/4 of the total length. These show you where the current nodes occur for 20, 15 and 10 meter operation. Try to make your bends at one or more of these points to get the more effective radiation pattern of full half wave(s) at whatever harmonic you want to use. The wire radiates as four half waves end-to-end when operating on 20 meters.

I keep learning stuff I never thought about in this thread. Right now the antenna is strung around the room so I can listen. When I get time to install it in the attic and start transmitting I'll definitely keep this in mind.

Speaking of transmitting, I figure I should add a choke to the feed line so I don't burn myself. Is there any reason to choose a removable choke vs. just wrapping the feed line itself through a toroid? Are there situations where I would *not* want a choke?

 

[kk4obi]

An end-fed half-wave antenna is actually operating around 5 to 7 percent from the end (look up “end effect”). The coax cable provides the missing length. A choke near the feed point kills that radiating part and screws up everything. Put a section of coax at least 7% long on the end and attach a broad band choke there. Coiled coax is narrow band. Do not use.

 

[prcguy]

I've done a lot of experimenting with both home made EFHWs and the commercial versions from MyAntennas using no common mode choke, then one 10-20ft down the feedline from the transformer then one right at the transformer. Nobody could tell the difference on air and I did not see any change in VSWR when in the resonant areas of the antenna. If you try to use the EFHW waay out of band then it will light up the coax and placement of the choke might come into play.

An end-fed half-wave antenna is actually operating around 5 to 7 percent from the end (look up “end effect”). The coax cable provides the missing length. A choke near the feed point kills that radiating part and screws up everything. Put a section of coax at least 7% long on the end and attach a broad band choke there. Coiled coax is narrow band. Do not use.

 

[N8MXL]

An end-fed half-wave antenna is actually operating around 5 to 7 percent from the end (look up “end effect”). The coax cable provides the missing length. A choke near the feed point kills that radiating part and screws up everything. Put a section of coax at least 7% long on the end and attach a broad band choke there. Coiled coax is narrow band. Do not use.

I've done a lot of experimenting with both home made EFHWs and the commercial versions from MyAntennas using no common mode choke, then one 10-20ft down the feedline from the transformer then one right at the transformer. Nobody could tell the difference on air and I did not see any change in VSWR when in the resonant areas of the antenna. If you try to use the EFHW waay out of band then it will light up the coax and placement of the choke might come into play.

I plan to use a counterpoise once I'm setup to transmit. As I understand it (correct me if I'm off-base here) that negates the need for the coax to provide the missing length, or I'll put the choke near the rig so the coax can cover that task if necessary. I did some digging and it seems like a bisectional bifilar wound choke would do the job and cover all the HF bands. I already have a 140-43 core and some connectors, so I'd just need a few feet of wire and an enclosure to build one (half the fun in my world).

 

[prcguy]

The bifilar wound core sounds like your making a 9:1 transformer. An EFHW is an End Fed Half Wave and not to be confused with a random "magic" length of wire connected to a 9:1 transformer. The EFHW is very high impedance, somewhere between 2,500 and 3,200 ohms (as it should be) and its resonant and radiates basically the same as a center fed dipole of the same length. It doesn't really require a counterpoise when used on its resonant bands which is basically all harmonically related bands. You also don't need a tuner in most cases, the match is very good at resonance.

A 9:1 with whatever length of wire requires a tuner and a counterpoise, which is usually the coax and the coax radiates and its hot. There is a very noticeable performance difference between a resonant EFHW and a 9:1 type favoring the EFHW. If you want to make an actual EFHW look for plans to make a 49:1 or 64:1 transformer to properly match the end fed resonant half wave or half wave multiple.

Just because both these antennas are end fed doesn't mean the work the same, they do not!

I plan to use a counterpoise once I'm setup to transmit. As I understand it (correct me if I'm off-base here) that negates the need for the coax to provide the missing length, or I'll put the choke near the rig so the coax can cover that task if necessary. I did some digging and it seems like a bisectional bifilar wound choke would do the job and cover all the HF bands. I already have a 140-43 core and some connectors, so I'd just need a few feet of wire and an enclosure to build one (half the fun in my world).