Moonraker 5/8 Wave FALSE specs claiming 4.5dBd of gain!

[teckniqs]

Someone I know recently bought one of these aerials to use with his 120w TX and asked me what the ERP would be.

As far as I remember a 5/8 antenna is usually around 2dBd of gain which technically should mean about 66.7 (two thirds) of extra gain.

....However looking at the Moonraker website, it appears to show a complete lie claiming that the antenna is 4.5dBd of gain!

As far as I am aware a dipole is 0dBd of gain but has 2.14dBi of gain - so I expect the 4.5 of gain Moonrakers are claiming should have been dBi and an extra 2.36dBi of gain over a dipole?

I have never used these aerials and don't really know much about them, but I'm sure I know enough to know that there is no way it can be as much as 4.5dBd of gain?

https://www.moonraker.eu/bm108-fm-88-10 ... ar-antenna

[Electronically]

Someone I know recently bought one of these aerials to use with his 120w TX and asked me what the ERP would be.

As far as I remember a 5/8 antenna is usually around 2dBd of gain which technically should mean about 66.7 (two thirds) of extra gain.

....However looking at the Moonraker website, it appears to show a complete lie claiming that the antenna is 4.5dBd of gain!

As far as I am aware a dipole is 0dBd of gain but has 2.14dBi of gain - so I expect the 4.5 of gain Moonrakers are claiming should have been dBi and an extra 2.36dBi of gain over a dipole?

I have never used these aerials and don't really know much about them, but I'm sure I know enough to know that there is no way it can be as much as 4.5dBd of gain?

https://www.moonraker.eu/bm108-fm-88-10 ... ar-antenna

Your absolutely spot on technics there is no way the 5/8 wave can achieve 4.5. I had a rough idea it was around 3 but 2 is probably more correct in what you have said.

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[Albert H]

They should be claiming 4.5dBi - that might be about honest.

The ⅝-wave is good for low sites, but can be tricky to match. I really can't see what people have against the single slot colinear (see Harry's Homebrew Homepage). It's an easy aerial to build, shows significant gain over a dipole, and is really easy to match. I've used them by the dozen, and they've always worked well. One of our guys was building them out of slotted steel tubes that were designed for the rails of shelving. He made them adjustable, so it was easy to tune for any part of the band. Each one cost about £15 to make.

[Electronically]

Yup 5/8 waves are made for low locations. If you was so high up with a line of site using your 5/8 wave then half your power is lost to the clouds.

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[Albert H]

The ⅞-wave with a capacity "hat" and the correctly adjusted ground radials goes fairly flatly towards the horizon. I used one up a block in South-East London, and had a huge signal in Essex! It was an interesting experiment.

[teckniqs]

Thanks for the replies, I didn't think for one moment it could be as much as 4.5dBd gain.

....And interesting that they work better on lower sites, I've seen a few Veronica 5/8 wave used for legal community stations from small tower blocks but never seen them being used by stations on high ground (tall hills with masts on etc).

[Albert H]

I've used them quite a lot over the years, but in reality they were usually 0.64-wavelength aerials. Look it up - the 0.64 antenna is one of the "secrets" of military communications.

I really do prefer J-poles, slim-jims and colinears (where practical). The coaxial colinear can have spectacular gain, an omnidirectional radiation pattern and can be disguised as something else!

[Electronically]

Yup a 0.64 wave antenna is the highest gain single element design available anywhere with at least a 0.8 dB/d of gain towards the horizon, than any 5/8 wave element.


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[Electronically]

Interesting.

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[Electronically]

5/8 wave is a 0.62 wave. In which case 0.64 is slightly longer in element.

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[Albert H]

The extra 2% does make a difference!

[Electronically]

Does make a difference but if the radials are made at 1/4 wave of wave length. And the matching network loading coils are a match then technically you could throw your centre pole at the 0.64 length which will give you more gain due to its length is taller due to the matching network allowing you to do this. But I've heard these at lengths of 0.64 can burn out quicker I dunno if it's true. Can any shed some light on this to see if I'm right or not?

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[RF-Head]

Look at the instruction manual of the moonraker
the elements is in 2 parts with a loading coil in the middle
but than it has a strange length if it's 2 times 5/8

[Electronically]

Look at the instruction manual of the moonraker
the elements is in 2 parts with a loading coil in the middle
but than it has a strange length if it's 2 times 5/8

There is a loading coil at very bottom of end fed tapped on second turn and as you said there in middle is a coil too. Unless there is two versions of it with one coil in middle and other antenna with two coils.

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[teckniqs]

As far as I can see it's only got this one coil down at the base of the antenna at the feeder point connection.

....The aerial is indeed quite long though and as you can see it reaches all the way from the front cabin of a transit size van all the way to the rear.

Anyway a quick update in regards to the suggestions from this thread, I have suggested that he just uses this 5/8 antenna from a lower site and will now be looking into using something else as it will be from a higher site.

[teckniqs]

Actually no ignore that ^

....I just spoke to him and he said yeah there is a coil half way along the main element as well. (But I didn't notice it)
He's hopefully gonna send me a picture of it shortly.

[Electronically]

Middle coil and loading coil same, as yours technics bottom part.

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[teckniqs]

same, as yours technics

OK fair enough but it doesn't belong to me, it's not mine. I would never buy anything from Moonraker.

...That red wire on yours (or who ever that belongs to) looks like it's got pretty hot.

[Electronically]

same, as yours technics

OK fair enough but it doesn't belong to me, it's not mine. I would never buy anything from Moonraker.

...That red wire on yours (or who ever that belongs to) looks like it's got pretty hot.

It's no been used on a 350 watt iron lol

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[Electronically]

same, as yours technics

OK fair enough but it doesn't belong to me, it's not mine. I would never buy anything from Moonraker.

...That red wire on yours (or who ever that belongs to) looks like it's got pretty hot.

It's no been used on a 350 watt iron lol

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Saw it on ebay going for 40 quid so took it. Yea wire came like that. I can't complain for the price. I could easily replace the red wire for a newer wire to freshen it up thought.

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