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Moonraker antenna?
Posted: Sat Nov 30, 2019 1:01 pm
by s2000
Just wondered if anyone had ever tried one of these?
https://www.moonraker.eu/bm108-fm-88-10 ... ar-antenna
Seems to have good gain (compared to a dipole), only drawback seems to be the low power handling.
Are they any good?
Re: Moonraker antenna?
Posted: Sat Nov 30, 2019 1:27 pm
by sinus trouble
Haha!! I like their bonus point system.... Measured in Watts!
Re: Moonraker antenna?
Posted: Sat Nov 30, 2019 6:41 pm
by livendirect
seen these a while ago worth a try
Re: Moonraker antenna?
Posted: Sat Nov 30, 2019 7:33 pm
by BriansBrain
I just get...
Error.JPG
Re: Moonraker antenna?
Posted: Sat Nov 30, 2019 7:46 pm
by Tec1 87.5fm London
Shit don’t work good
Re: Moonraker antenna?
Posted: Sat Nov 30, 2019 9:35 pm
by fmuser877
web site fine for me on BT
Re: Moonraker antenna?
Posted: Sun Dec 01, 2019 9:06 am
by teckniqs
BriansBrain wrote: ↑Sat Nov 30, 2019 7:33 pm
I just get...
Error.JPG
Seems to work fine for everyone else.
.....Are you using Microsoft Edge or some shitty browser like that?
Re: Moonraker antenna?
Posted: Sun Dec 01, 2019 9:07 am
by teckniqs
4.5dB gain sounds a bit extreme
Re: Moonraker antenna?
Posted: Sun Dec 01, 2019 12:07 pm
by BriansBrain
teckniqs wrote: ↑Sun Dec 01, 2019 9:06 am
BriansBrain wrote: ↑Sat Nov 30, 2019 7:33 pm
I just get...
Error.JPG
Seems to work fine for everyone else.
.....Are you using Microsoft Edge or some shitty browser like that?
Nah... I am in Gran Canaria, Spain.
I have sorted it now by doing some re-routing
Re: Moonraker antenna?
Posted: Sun Dec 01, 2019 2:54 pm
by Albert H
I gave one of these a try a little while ago. I needed an omni-directional aerial for a local filler (40 Watts), and this looked like it might do the job.
When it arrives, it's cut to length for just below 88 MHz. I wanted to use it on 88.1 MHz, so didn't bother with cutting it. The SWR at 88.1 MHz - straight out of the box - was 1.065 : 1. The match showed little reactance. I mounted on my test "tower" and I fired the 40 Watts into it, and everything was fine.
I decided to check field strength against a Pawsey Stub Dipole made for the same frequency. Their 4.5 dBd is rather optimistic. I'd guesstimate that it's closer to 3.5 dBd, but it's still useful gain, and the aerial doesn't look like a dipole. This is a big win for clandestine use!
It's well made, and looks like it'll stand up to bad weather. Ours has been installed on site (two weeks ago) and the customer is happy with the results. We turned down the power on his rig so that the power consumption is reduced, and the rig runs cold. We have 25 Watts out of the box, into 35m of UR67, then the antenna at 44m above ground in free space. It gives almost exactly the same result as 40 Watts into a gamma-matched dipole at the same elevation. Field strength below the antenna is low, suggesting that the groundplanes are doing their job.
At £70 it's a bit expensive, but it saves the hassle of building something and it doesn't look like the obvious dipole!
Re: Moonraker antenna?
Posted: Sun Dec 01, 2019 4:27 pm
by BriansBrain
Albert H wrote: ↑Sun Dec 01, 2019 2:54 pm
I gave one of these a try a little while ago. I needed an omni-directional aerial for a local filler (40 Watts), and this looked like it might do the job.
When it arrives, it's cut to length for just below 88 MHz. I wanted to use it on 88.1 MHz, so didn't bother with cutting it. The SWR at 88.1 MHz - straight out of the box - was 1.065 : 1. The match showed little reactance. I mounted on my test "tower" and I fired the 40 Watts into it, and everything was fine.
I decided to check field strength against a Pawsey Stub Dipole made for the same frequency. Their 4.5 dBd is rather optimistic. I'd guesstimate that it's closer to 3.5 dBd, but it's still useful gain, and the
aerial doesn't look like a dipole. This is a big win for clandestine use!
It's well made, and looks like it'll stand up to bad weather. Ours has been installed on site (two weeks ago) and the customer is happy with the results. We turned down the power on his rig so that the power consumption is reduced, and the rig runs cold. We have 25 Watts out of the box, into 35m of UR67, then the antenna at 44m above ground in free space. It gives almost exactly the same result as 40 Watts into a gamma-matched dipole at the same elevation. Field strength below the antenna is low, suggesting that the groundplanes are doing their job.
At £70 it's a bit expensive, but it saves the hassle of building something and it
doesn't look like the obvious dipole!
Very useful information
Albert H ... thanks very much
Re: Moonraker antenna?
Posted: Sun Dec 01, 2019 4:50 pm
by teckniqs
Although I've not used one myself, my pal said he has used one and he wasn't too impressed with it. He says he changed it to a Sirio Gamma Matched Dipole and claims the signal was much better with the gamma than with the 5/8.
....This was from a tower block on high ground around West London area and he says he picked it up all the way to Stone Henge with the gamma but only heard it as far as Basingstoke with the 5/8 (about half the distance!)
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 2:18 am
by Albert H
Did your pal bother to tweak the overall length to get it to resonate properly? If it's the wrong length, the match is horrible and the losses mount up. When I tried the one here, I tuned the rig up to 91 MHz, with the antenna at its original 88 MHz length. The match was about 2.2 : 1 so there was no significant gain over a dipole at that point. At 93 MHz, it was almost 3 : 1, so not worth using. It's essential to follow the cutting chart for your frequency of choice!
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 9:13 am
by teckniqs
No he didn't, he got the well known builder "N" to do it for him using his aerial network analyser, same as with the Gamma Matched Dipole.
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 9:28 am
by RF-Head
I have opend the base of the antenna to see the matching coils and they look like they cant handle 200W also there is a ceramic capacitor in the matching circuit
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 3:30 pm
by ronald001
This is a rebranded comet antenna (Comet CFM95SL)
Someone i know is using it, and it performs quite well
Not sure how much power it wil handle
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 6:07 pm
by RF-Head
Hi Ronald
No it's not a comet.
The matching parts is not the same and the ground elements are pointing down
I have a comet and yes it's working great
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 8:57 pm
by s2000
Thanks for the replies.
I had a look at the "comet", the specs seem to all be the same except for the gain figure. On the comet is says its 3.4dbi? So thats 1.25dbd if I am correct?
https://www.k-po.com/COMET-CFM95SL.2.html
How can two antennas that are almost the same, have completely different gains?
I suppose what I am looking for is something discrete with omnidirectional coverage and a
minimum of 3dbd gain. Also it would be nice not to have endless issues like the feedline radiating and reacting with the mast etc.. Can such an antenna be purchased for reasonable money?, or does it mean building?
I am not against building one and have made a few before but it would be nice if something was readily available (especially in this weather)
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 9:35 pm
by livendirect
i have ordered one to compare with a dipole going to use same pole and coax see what the difference is
Re: Moonraker antenna?
Posted: Mon Dec 02, 2019 10:30 pm
by Albert H
ronald001 wrote: ↑Mon Dec 02, 2019 3:30 pm
This is a rebranded comet antenna (Comet CFM95SL)
Someone i know is using it, and it performs quite well
Not sure how much power it wil handle
It's NOT the "Comet" - it's a colinear. The "Comet" is just a ⅝-wave vertical with groundplanes.