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Apartment antenna question for uBitx #ubitx

ashok.das81@...
 

Dear all,

I live on the top floor of a 3 story apartment. I do not have any other space for antenna except the rooftop. To set up a dipole antenna I made a plan i have attached below. I will use common PVC insulated household electrical wire approx 3-4 sqmm dia, for antenna. I will use a uBitx transceiver and tx power will not be much (Maximum that uBitx support). I am requesting you to suggest/advice me how this antenna will perform and also advise me to make balun/matching transformer/antenna tuner for this antenna. Thick black wire is coax and thick blue wire is antenna.

Regards
Ashok

Curt
 

Shorten each vertical wire by 6 feet. This will make antenna play on 7 and 21 MHz. Perhaps add a parallel wire 16.5 feet on each side for 14 Mhz. This seems an easy antenna for coax feed.

An FD3 antenna with off center feed could work, but it needs a balun at feed point, or ladder line instead of coax and an antenna tuner.
Curt

Gordon Gibby <ggibby@...>
 

That looks like a great antenna and I bet you will have a Lotta fun.   If you have some way to measure the standing wave ratio, that will help.  I buy used Citizen band SWR meters for about $15 at Hamfest‘s to help people new to HF to get going. there are also some models on Amazon for $15-$20 that work fine

If your building has a good bit of metal on its roof as many buildings do, don’t be surprised if the antenna is a little lower impedance than one would expect.   

I’ve worked with antennas on top of university buildings which exhibited as low as five or 10 arms impedance at resonance, instead of the expected 50 to 75

I’m suspecting this is because energy was coupling into nearby long metal part of lightning arrester systems or building water protection flashing



On Aug 25, 2019, at 08:11, Curt via Groups.Io <wb8yyy@...> wrote:

Shorten each vertical wire by 6 feet. This will make antenna play on 7 and 21 MHz. Perhaps add a parallel wire 16.5 feet on each side for 14 Mhz. This seems an easy antenna for coax feed.

An FD3 antenna with off center feed could work, but it needs a balun at feed point, or ladder line instead of coax and an antenna tuner.
Curt

G1WDF
 

Why not consider a horizontal loop above the building. Less visual impact, and keeping the ends of the AERIAL away from your nieghbours flats and passing pedestrians.

Good luck.

Jack, W8TEE
 

How about a mag loop?

Jack, W8TEE

On Sunday, August 25, 2019, 1:28:00 PM EDT, G1WDF <wobblyandflo@...> wrote:


Why not consider a horizontal loop above the building. Less visual impact, and keeping the ends of the AERIAL away from your nieghbours flats and passing pedestrians.

Good luck.

bobolink
 

I’m no antenna expert but my guess is that the max radiation will be at right angles to the plane of the wire. Are those good directions to the stations you want to reach?

Ken Hansen
 

With loop antennas you want to keep possible noise sources outside of the loop, a roof mounted loop might pick up tremendous noise from roof mounted A/C, etc.

On the the other hand, the highest-energy points on this antenna will be at the ends, which you've drawn within arms reach of anyone near the ground.

Every antenna is a compromise, I just wanted to add that information into your decision process as you choose your compromises.

Remember, the worst antenna is the one that stays in the box, any deployed antenna is better than that!

Quick thought, what about putting a 20/40 meter fan dipole across the roof of the apartment building?Possibly consider a rotatable dipole, even if mounted static/stationary. Something that only requires one mounting point, is self-supporting, and could cover several bands.

Ken, N2VIP

On Aug 25, 2019, at 12:27 PM, G1WDF <@wobbly> wrote:

Why not consider a horizontal loop above the building. Less visual impact, and keeping the ends of the AERIAL away from your nieghbours flats and passing pedestrians.

Curt
 

The first reason for shortening is the classic length equals 468 divided by frequency, yes Ashok gave dimensions in feet. Second reason I forgot to type, it keeps the lowest part of wire 9 feet above the ground. Interesting point by Gordon on what if much of building is metal,  maybe its not.

When center fed, peak current tends to be near center, with voltage peaking at the ends in case of a half wave dipole. Not fun to touch any place at100 watts.

Occupied building best to use a qrp when radiation is close to people, and their electronics.

Curt

Jack, W8TEE
 

Ken:

Won't just about any antenna suffer from noise from an AC unit and other sources. We've been experimenting with this unit:

Inline image

and find it to be pretty quiet, as are most loops. This loop is remote controlled and only 3' in diameter. There are a lot of small commercially available loops that could be kept in the apartment and tuned by hand or by remote.

Jack, W8TEE

On Sunday, August 25, 2019, 2:09:59 PM EDT, Ken Hansen <ken@...> wrote:


With loop antennas you want to keep possible noise sources outside of the loop, a roof mounted loop might pick up tremendous noise from roof mounted A/C, etc.

On the the other hand, the highest-energy points on this antenna will be at the ends, which you've drawn within arms reach of anyone near the ground.

Every antenna is a compromise, I just wanted to add that information into your decision process as you choose your compromises.

Remember, the worst antenna is the one that stays in the box, any deployed antenna is better than that!

Quick thought, what about putting a 20/40 meter fan dipole across the roof of the apartment building?Possibly consider a rotatable dipole, even if mounted static/stationary. Something that only requires one mounting point, is self-supporting, and could cover several bands.

Ken, N2VIP

> On Aug 25, 2019, at 12:27 PM, G1WDF <wobblyandflo@...> wrote:
>
> Why not consider a horizontal loop above the building. Less visual impact, and keeping the ends of the AERIAL away from your nieghbours flats and passing pedestrians.



Gordon Gibby <ggibby@...>
 

For my two cents, you guys are hilariously overthinking this.   Put the longest where are you can put up, find some dadgum way to match it  and get some watts going into it.   Go look at the allowable distance from an HF antenna running up to two or 300 W and you’ll find for HF it is measured in inches and feet.   

If you’re going to run QRP, you want the most efficient antenna you can think of, and everybody knows what that is.   

Let the poor guy start having fun with ham radio


On Aug 25, 2019, at 14:33, Jack Purdum via Groups.Io <jjpurdum@...> wrote:

Ken:

Won't just about any antenna suffer from noise from an AC unit and other sources. We've been experimenting with this unit:

<Figure 1 Alt01_.jpg>

and find it to be pretty quiet, as are most loops. This loop is remote controlled and only 3' in diameter. There are a lot of small commercially available loops that could be kept in the apartment and tuned by hand or by remote.

Jack, W8TEE

On Sunday, August 25, 2019, 2:09:59 PM EDT, Ken Hansen <ken@...> wrote:


With loop antennas you want to keep possible noise sources outside of the loop, a roof mounted loop might pick up tremendous noise from roof mounted A/C, etc.

On the the other hand, the highest-energy points on this antenna will be at the ends, which you've drawn within arms reach of anyone near the ground.

Every antenna is a compromise, I just wanted to add that information into your decision process as you choose your compromises.

Remember, the worst antenna is the one that stays in the box, any deployed antenna is better than that!

Quick thought, what about putting a 20/40 meter fan dipole across the roof of the apartment building?Possibly consider a rotatable dipole, even if mounted static/stationary. Something that only requires one mounting point, is self-supporting, and could cover several bands.

Ken, N2VIP

> On Aug 25, 2019, at 12:27 PM, G1WDF <wobblyandflo@...> wrote:
>
> Why not consider a horizontal loop above the building. Less visual impact, and keeping the ends of the AERIAL away from your nieghbours flats and passing pedestrians.



<Figure 1 Alt01_.jpg>

Curt
 

I entirely concur with Gordon. Stay with wire as originally configured, while I have worked a few using those small magnetic loops they require heroic acts to copy cw from. Touching the wire is the greater hazard at 5 or 10 watts, fortunately no one seems to be over 8 or 9 feet tall. Ashok please report back or email any of us as required.

Curt wb8yyy

John Faivre
 

That looks great Jack. Are you going to sell a kit?
--
John Faivre WA9SGD

Jack, W8TEE
 

The construction of the Luggable Double-Double (it's sorta portable) is the subject of Chapter 17 in our new book and Chapter 18 is on the remote control unit. Both are Open Source and there will be a PCB available for the remote unit. We have tested it pretty extensively (Field Day and reverse beacon) and it works pretty well. It works on 40, 30, and 20 meters and we can get down to 1.1:1.0 on all bands and efficiency on 40M is a little over 40%. It's double that on 20M. No need for a kit as the tubing and parts are available at Lowes and the electronics is all common stuff.

Jack, W8TEE



On Sunday, August 25, 2019, 8:22:12 PM EDT, John Faivre <wa9sgd@...> wrote:


That looks great Jack. Are you going to sell a kit?
--
John Faivre WA9SGD

Jack, W8TEE
 

 I would even consider using a ML that didn't have remote tuning. Body capacitance can change things significantly and tuning with a stick is cumbersome at best. Also, the efficiency of a small single loop is not that great.

Jack, W8TEE


On Sunday, August 25, 2019, 4:42:12 PM EDT, Curt via Groups.Io <wb8yyy@...> wrote:


I entirely concur with Gordon. Stay with wire as originally configured, while I have worked a few using those small magnetic loops they require heroic acts to copy cw from. Touching the wire is the greater hazard at 5 or 10 watts, fortunately no one seems to be over 8 or 9 feet tall. Ashok please report back or email any of us as required.

Curt wb8yyy

ashok.das81@...
 

Wow, that's so many ideas, thanks all nice people

I will try to study and understand each of these and come back to you if I need any more support. I will work QRP, my rig is uBitx.

Regards
Ashok

ashok.das81@...
 

Dear Curt & G1DF,

Can I get some good literature on FD3 and Horizontal loop antenna, a quick search on internet did not come up with any good resource.

Regards
Ashok

_Dave_ K0MBT
 

One of my antennas is an end fed half wave. It uses a unun 49:1 to feed 63-64 feet of wire at the end. The advantage is that it is resonant on 40, 20 , 15 and 10 meters. Okay without a tuner.  Run the unun hanging outside your window and down toward the other side of the building.   Put your roof mounts at at least some inches from the steel posts. 

The rf on the antenna of a uBITX is uncomfortable. Keep it out of reach. 

Curt
 

Ashok

Use your search engine to find 'FD3 antenna' and 'FD4 antenna' - I see many hits.  This antenna was developed in Germany, although others likely advanced it also.  It will match on even and odd harmonics - but it requires a complex balun at the feedpoint.  (Note the FD3 will also be around 66 feet total length for operating on 7 MHz and above). 

Also the end- fed half wave dipole arrangement that was mentioned is also a good multi-band choice.  Many QRP examples on the web.  If you are in North America, see QRPGUYS.com website for kits - but they can be homebrewed easily for QRP levels. 

With any antenna - we suggest placing it out of reach from the ground - to avoid an RF burn if someone touches it while you are transmitting. 

The problem with the horizontal loop is that it needs a full wavelength of wire.  For 7 MHz it is around 1005 / 7 = 143 feet circumference - much too large to fit on your roof. 

Your center fed dipole isn't bad if you adjust it to around 468 / 7 = 66 feet total length, but it will not match also on 14 MHz.  Please note the end fed half wave will be about the same length - but the feed is direct on the end.  It does not seem to fit your building as well as the center fed. 

A key principle when using coax -- it works best when the antenna feed point is matched to it.  It can be replaced with twin lead (300 ohm or higher impedance) to allow operating on any band - but you need an antenna tuner.  Many QRP antenna tuners are sold as kits or homebrew.  Maybe start with coax on a single band - and later consider twin lead.  With twin lead you can center feed or off-center fed similar to the FD3.  With coax and no 'matching balun' at the feedpoint - stay with center feed. 

Curt

f1mqj
 

Perhaps you could try windom/OCFD
https://www.aerial-51.com/model-404-ul/
http://www.dj0ip.de/off-center-fed-dipole/40m-ocf/version-2-2/
https://hamwaves.com/cl-ocfd/en/index.html
They seem work fine on 40-20-15-10 m without tuner, 17/12 with tuner, 30m perhaps, and can work bended (cf hamwaves)
there could be a large part of personal experiment ... to check the better for your environment (the main default of these antenas is the environment dependancy, especialy with wall/roof...)
73 - Remi - F1MQJ

Tom, wb6b
 

On Tue, Aug 27, 2019 at 09:58 AM, f1mqj wrote:
aerial-51.com
That is a clever name.

Also:
You could try one of the end-fed non-resonate antenna designs with a 9 to 1 unun. Depending on the bands you want to work you can use a 55 or 40 foot wire. The coax is intentionally a radiating counterpoise, so you need to put a choke on the coax at around 50 foot from the antenna (before it enters your shack). 

My experience with antennas too close to the house is (at least at 150 watts) is transmitting trips some of my GFI protectors and sets off one of my smoke alarms. As well as picks up noise from many of the switching supplies from the various wall warts plugged in around the house. 

QRP is likely to be a big benefit as far as relations with your apartment neighbors are concerned.

Tom, wb6b