Last week we looked at the stock Lawmate 1.2GHz Transmitter antennas which was very good for one channel, not so great for pretty much anything else. This week we're going to take a look at an option from DragonLink. They call this a video Transmitter antenna, however there is no reason why it cannot be used on a receiver as well. These are the same style as the 433MHz receiver antennas.
I'm reviewing this in two flavours, the direct SMA mount version, and the 3cm hardline version. Flights have been made over 100km away with these on the transmitter, so expectations are high.
For all of these tests, I'll add markers 1 and 2 at 1.25:1 (1.235% loss), and markers 3 and 4 at 1.5:1 (4% loss). You can see the frequencies that these match at in the top right of the pictures. A VSWR of 1.25:1 is very good, even 1.5:1 is good, however most antenna manufacturers would consider this to be a poorly matched antenna.
We're not testing in an anechoic chamber, however other than that all antenna testing best practices are applied.
So how does the antenna look?
Direct SMA mount, 1.5:1 range, 1.17GHz to 1.27GHz, best frequency 1.21GHz with a 1.15:1 VSWR.
3cm Hardline mount, 1.5:1 range 1.17GHz to 1.24GHz. Best frequency 1.2GHz at 1.34:1 VSWR.
This is interesting, as these are balanced dipoles the cable should have no effect at all on the tuning of the antenna. I know that these antennas are hand made and hand tuned, rather than mass produced by CNC equipment in a factory so there will be variation between each unit. That lead me to the next test of the 3CM version:
Thats quite a low VSWR, guess what - I'm hold it as if I was trimming the elements to tune it, I suspect someone didn't realise that you have to have an antenna without anything conductive or capacitive (like a human body) around it.
The response is certainly better than the Lawmate unit, with a flatter curve. I suspect the majority of people would be interested in using these for 1280MHz in the USA, so that would mean that these are tuned to a frequency slightly too low. For the antennas I have, this means a quick trim off the ends can bring these into spec pretty easily, with about 15 seconds of trimming:
Note, I changed the stop point up 200MHz and the start point up 100mhz to better see the response when tuning. Marker 5 is at 1280MHz.
I could have taken a smidge more off, but this way the antenna is good for 1258MHz and 1280MHz. 1.50:1 is 4% loss, so this is still better than the stock Lawmate transmitter antenna.
My rating: Better than average. It beats the stock antennas for the frequency it is designed for (don't use it for 1080mhz), but may not be precisely tuned.
This is a pretty cheap antenna, and is much more streamlined than the gigantic and fragile circular polarised antennas for 1.2GHz. A CP Antenna is not needed at this frequency, and will be out of tune as soon as you bump the lobes too much.
Where can you buy one?
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