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2Bay or not 2Bay ? - - - that is the Question

Posted: Sun Jul 14, 2019 3:41 pm
by BriansBrain
2Bay or not 2Bay ?

This is my Question :roll:

This is what I have now with my height limitations to go 2Bay :cry:

Antenna is 4M above building and a total of 8.2M from Ground Level

This is my Question... do I have enough height to go 2Bay without problems :?

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Tue Jul 16, 2019 12:51 pm
by BriansBrain
This is what I have available

Am I going to have a tuning or SWR problem ?

All to Scale :shock:

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Tue Jul 16, 2019 4:13 pm
by NOYB
Just wondering why the bother for just 3dB gain - are you trying to minimise downward radiation locally?

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Tue Jul 16, 2019 7:15 pm
by BriansBrain
NOYB wrote: Tue Jul 16, 2019 4:13 pm Just wondering why the bother for just 3dB gain - are you trying to minimise downward radiation locally?
It will be 6dB Gain :whistle ... going from 150W > 300W :tup

And Like you say... I'd like to minimise the local downward radiation :roll:

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Tue Jul 16, 2019 9:22 pm
by Banus_radio
Take my word and use a Super J-Pole. Similar gain and nice doughnut shape radiation.

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Tue Jul 16, 2019 9:58 pm
by sinus trouble
Just to add, Your mast should be a quarter wave above your boom (Level with top element) to be theoretically balanced!

Some may disagree?

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Wed Jul 17, 2019 2:45 am
by Albert H
Delete this one please.

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Wed Jul 17, 2019 2:46 am
by Albert H
With a twin, the lower dipole needs to be at least a wavelength away from the building structure - you're going to need a bigger pole!

The "Super-J" would probably suit your site better, and would give you significant gain (if properly matched). It also has very little downward radiation, so there's little risk of local interference or overloading problems.

The big trick - whatever antenna you use - is to get the damn thing as high and as far as possible from the structure of the building!

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Wed Jul 17, 2019 10:42 am
by BriansBrain
sinus trouble wrote: Tue Jul 16, 2019 9:58 pm Just to add, Your mast should be a quarter wave above your boom (Level with top element) to be theoretically balanced!

Some may disagree?
Now...... I did not know that....... thanks :tup

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Wed Jul 17, 2019 10:55 am
by BriansBrain
Albert H wrote: Wed Jul 17, 2019 2:46 am With a twin, the lower dipole needs to be at least a wavelength away from the building structure - you're going to need a bigger pole!

The "Super-J" would probably suit your site better, and would give you significant gain (if properly matched). It also has very little downward radiation, so there's little risk of local interference or overloading problems.

The big trick - whatever antenna you use - is to get the damn thing as high and as far as possible from the structure of the building!
Thanks Mr 'H' ....... :smoke
I've always wanted a bigger pole ever since I was a teenager :lol:

Anyway..... I'm trying stay as Inconspicuous as possible, but I also thought I need to go higher...

How about like this... giving me an extra 1.3M
2 Bay Dipole-3 + Extra 1.3M.jpg
The "Super-J" you mean this one ? .... or another ?
on eBay >>> FM band 88 to 108 mhz jpole antenna
JPole.jpg
:whistle

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Wed Jul 17, 2019 12:16 pm
by BriansBrain
OK... :whistle

I have looked up the Super J-Pole Antenna
Here is a Calculator :smoke
http://www.hamuniverse.com/superjpolecal.html

For 'Brian' @ 96.8MHz this Antenna would have to be nearly 3.7M tall :roll:
Super J-Pole Antenna - in M-s.jpg
I have also looked here...
https://www.hamradio.me/antennas/improv ... per-j.html

Where is stated...
Some web sites suggest the Super-J has a full 3 dB gain over the plain J-Pole which is a pretentious claim obvious to anyone with a copy of the ARRL Antenna Book and other references. Indeed, the Super-J will never approach the gain advantage of a properly separated two element collinear antenna, but we can get closer to this goal.
:?

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Thu Jul 18, 2019 1:48 pm
by Albert H
Getting your twin stack that bit higher will help, but a good vertical colinear would be even better.....

The Super-J is a reasonably easy aerial to build, but the centre matching section always weakens the aerial, which might pose a problem out at sea as you are.

You could consider a ⅝-wave or a ⅞-wave according to high up your site is. These can be made to look (almost) like base-loaded CB aerials, so they're really good for keeping a low profile. Look at the radiation angle you want, and decide on the antenna.

Each will require ¼-wave ground planes (minimum 3, 4 is better, but 6 is great!) angled downwards (the angle affects the match somewhat). This type of aerial also gives you other advantages - low radiation downwards into the building, low field strength in the immediate vicinity (confuses people trying to track it down) and it is an unbalanced aerial, so no balun is required. There are plenty of on-line calculators that will work out the dimensions for you and the number of turns on the matching coil.

These groundplane types are commonly used for amateur repeaters and commercial PMR base stations, where the operators want fully omnidirectional coverage, useful antenna gain, and a robust, easily constructed, aerial.

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Sat Jul 20, 2019 11:46 am
by BriansBrain
Thanks for the suggestions Mr H :tup

But....
2Bay or not 2Bay ? - - - that is the Question

Geographic coordinates of Maspalomas, Spain
Latitude: 27°45′38″ N
Longitude: 15°35′09″ W
Elevation above sea level: 32 m = 104 ft

This is one of my biggest problems :(

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Sun Jul 21, 2019 2:57 pm
by teckniqs
I think the best thing to do is just try adding the other bay and find out. :tup

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Mon Jul 22, 2019 1:33 am
by Albert H
Teckniqs suggestion of giving it a try is probably best! You MUST get the lower antenna as high as possible above the building roof, or you'll get a poor match and waste energy into the brickwork!

Another aerial with a helpful radiation pattern for you (with your low site) would be a Slim Jim.

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Mon Jul 22, 2019 12:36 pm
by BriansBrain
Thanks Teckniqs & Mr H :tup

After doing some more research I find that my Actual Elevation above sea level is only +/- 17M
So add my 8.2M pole and my Antenna is only 12M above sea level :lol:

I can't get my lower antenna in a 2Bay to high above the building roof because of keeping inconspicuous.

I might look into this - from eBay :whistle

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Mon Jul 22, 2019 2:37 pm
by thewisepranker
Build one, they're easy to build from standard parts from a plumbing shop, easy to tune and you'll get some satisfaction out of it. You'll have to tune the eBay one anyway. I'm not keen on those eBay ones - your coax will fill with water.

Re: 2Bay or not 2Bay ? - - - that is the Question

Posted: Sun Aug 11, 2019 3:12 pm
by BriansBrain
OK..........

I'm forgetting the idea........ for now anyway :smoke

We are moving house, up the local hill, which happens to be at 200M Altitude :tup

Therefore my Dipole will be at a total Altitude of 212M
Antenna Height Above Average Terrain (HAAT) = 125M

I will keep you informed :whistle

Terrain Profile