Is there any minimum mounting distance between FA 978 &1090 antennas I should I be aware of? Since neither are transmitting my initial thought is no. Mounting on a 60’ tower and would like to have my mounting brackets figured out before the day of installation.
Thank you!
I’m just an uneducated hick, but here’s what I did.
I used a 10’ stick of 1 inch EMT as a mast. I placed the 978mHz antenna on top of the mast. Then dropped 24 inches, and made an offset mount 24 inches long to mount the 1090 mHz antenna.
So far so good. I see traffic out to 290SM on the regular, and spotted a balloon on Saturday that was 349SM away, but it was also at 66,000’.
Good luck!
J
Thanks J. That’s about the same distances apart I was planning on.
My 1090 and 978 antennas (both FA sticks) are up in the attic parallel mounted 16" apart on opposite sides of a vertical 2’x6" roof support. I added the 978 antenna 15 months ago which didn’t change 1090 reception at all.
The minimum horizontal seperation of receiving antennas should be one wavelength, which for 1090 mhz is 27cm (11 inch) and for 978 mhz is 30cm (12 inch).
Therefore horizontal seperations of 16 inch of @phodge and 24 inch of @Jsbird69 are both ok.
Every cell phone contains at least four radios. These include radios for the primary cellular communications, GPS, Wi-Fi, and Bluetooth. Every radio needs its own antenna, so there are at least four antennas in a cell phone. These antennas are built on the printed circuit board.
Now considering the size of a modern cell/mobile phone, what do you think spacing would be between these at least 4 antennas built on phone’s pcb? 
CLICK ON IMAGE TO SEE LARGER SIZE
CELL PHONE ANTENNA PLACEMENT
Antennas can create mutual interference. A simple solution could mean either spacing the antennas wide apart or physically blocking the signal path. The first, however, requires more space, and the second would cause the antennas to miss signals from the blocked direction. A better solution is compact isolation, incorporated into the antenna design so that it stops the interference but also lets the desired signals through.
CLICK ON IMAGE TO SEE LARGER SIZE
Without some serious engineering analysis/understanding, it’s best not to use something like a cell phone as an analogy.
Just one point to illustrate why this could be misleading - 2.4G wifi and bluetooth are on the same band, they share the same antenna and radio.
The commonly accepted separation distances have been derived from many years of observations and theoretical analysis, but for the most part, relate to transmitting antennas. The derived rules of thumb give you a guide to avoid problems, but can be played with as much as you like.
If you are going to the effort of climbing a tower or other remote site, it’s just easier to get it right first time than have to revisit and fix a problem that could have been easily avoided.
Not relevant, but the pic shows two 5G antennas.
The phone is a Samsung S8 (flagship model 2017) - three years before Samsung first offered 5G.
That rule of thumb found by experience is what I have already told in my post before posting the case of a cell phone. I am quoting it below
The date 2017-02-22 marked on battery may possibly be the date of manufacture of the battery. The Phone model number is no where on this screenshot. Anyway, I have not marked the antenna and bands on this screenshot. It is the person who opened the phone and took the photo has marked it, and I believe that he knew what model he has opened and weather it has 5G or not.
By the way, as we are not going to use this screenshot for repairing the phone, and the purpose of this screenshot was to show there are many antennas cramped in a small space, your objection to 5G inaccuracy, even if valid, is irrelevant.
EDIT:
The source of this screenshot is from IEEE Spectrum, which is issued by IEEE (Institute of Electrical and Electronic Engineers of North America)
Thanks phodge. That’s very reassuring.
Interesting stuff on Bluetooth and 5G antennas. I’ll be moving next year and will likely have an external mast setup at the new place so good to know about the separation minimums.
Use mnimum seperation values of one wavelength (12 inch / 30 cm in case of 1090 mhz) only where physical / constructional constrains dont permit larger seperation. Otherwise it is better to use somewhat larger seperation than minimum.
Yes, indeed.
By posting the comments about cell phones, you seem to be contradicting yourself.
Au contraire.
If you squint, you can clearly read: SM-G950U which is the in-house number for the Samsung S8
(I have not the slightest interest when the battery was made)
Perpetuating an untruth does not make it any truer.
(yes, I realise this is the internet and that is not a widely held belief)
Allow me to convince you that “my objection is valid”
The real point I was trying to make is that a carfully crafted piece of hardware (like a cell phone) designed by dozens of skilled RF engineers doesn’t transfer easily to mere mortals.
For the rest of us, it’s best to give the antennas some elbow room.
The referenced IEEE Spectrum article is pretty interesting. For one thing, apparently they have filters built in to the antennas that filter out the unwanted bands.
Another source of interference to sensitive RF circuitry is the clock from the processor itself. I learned a lesson way back where the clock for the processor happened to be at the same frequency as one of the IF stages of the modem. Getting rid of that interference in some cases was very difficult.
Not part of the antenna, but I suspect this is the filter referred to
I’d love to know what kind of voodoo went into designing that!
Thank you for your effort to find out that the Samsung’s 2017 model S8 did not have 5G, to prove that your comment about 5G was valid.
But was it relevant to the key point of my post that cell phones have multiple antennas cramped inside a small space? If 2017 models did not have 5G, they did have at least 4 other antennas (primary cellular communications, GPS, Wi-Fi, and Bluetooth).
OK, I agree that screenshot was wrongly marked by someone, so let us ignore it, and consider the current models. Don’t current models have 5G antennas as well?
To be honest, I have no idea how many antennas a modern phone has - it may be only one with a multiplexer for all I know.
But if it does have more than one, doesn’t that serve to contradict your own statements of minimum separation?
The article was published in 2018 and the author talks about FUTURE 5G.
The article talks about cramming lots of little, size compromised antennas into very small spaces and doesn’t seem at all relevant to the thread topic…
As for how far between the antennas for receiving, i feel you would be better off studying Yagi’s papers which discuss the effect of a slightly longer or shorter conductive media a measured distance, in wavelengths, from a radiating element. This includes how far the radiating element is from the mast.
S
When there is ample space available like mounting on tower or mast or roof, then minimum clearance thumb rules should be followed. That is what I suggested in my first post.
However these thumb rules give a wrong impression to the inexperienced that this is absolute minimum and less than this clearance is not possible without troubles. To clarify this misunderstanding, I made my next post, in which I gave example of Cell phones which shows that this rule of thumb minimum clearance is not absolute, and antennas can be placed very close to each other in a space restricted situation, but require special isolation techniques.
I’ve just returned from Exmouth where we viewed the total eclipse of the sun yesterday
Exmouth is home to The Harold E. Holt Naval Communications Station.
The station transmits on 19.8kHz with a power of 1 megawatt.
19.8 kHz is a wavelength of over 15,000km and Western Australia is big enough and empty enough to fit that in but as you can see the towers are not that far apart.
I guess the US Navy doesn’t follow the rule of thumb either.
It’s a long wavelength but not that long.
Should be 15,000 meters.
