Author Topic: increasing range of 418Mhz Mark III with antenna mods?  (Read 750 times)

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Offline DaleReid

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increasing range of 418Mhz Mark III with antenna mods?
« on: December 06, 2017, 09:16:58 AM »
I helped a friend set up a 'spare' Mk III, non-LR station at his place.  House has metal siding.  The location of the station sensors was in his garden, about 150' away, line of sight, nothing in the way between it and his receiver module which is in a window where the sensor station can be seen.

Most of the time all is well, but occasionally, even with a fully charged nearly new battery, the dreaded dashes of no reception appear.

I know that at higher frequencies yagis can be helpful, and some lines even have these.  With this design the antenna seems to be an end fed whip, no coax connection.

Has anyone found a trick to increase gain enough to be worth the trouble for the older Mark IIIs?  There is only one receiver and if there was some trick to make the antennas directional it would certainly help.


Thanks for any chatter or comments on helpful tweaks.  I mention antenna mods since that seems logical but there might be other things to try (short of a linear amplifier on the sensor suite's output.)  And I'm not ruling out trying other tricks for the receiver mod antenna,either.  It's just that the location in the garden is about the only one,  and now the ground is frozen, along with the spot in his kitchen where he and his wife agreed that the display can go ties my hands a little bit in moving around for a sweet spot.

Dale
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Offline dupreezd

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #1 on: December 06, 2017, 06:09:33 PM »
Dale, if the station comes equipped with a helical coil antenna, you might be able to replace it with an external mounted whip antenna such as this which have more gain (typical 2 - 3 dB).

The nice thing about this one is it comes with a piece of co-ax attached.
http://www.glolab.com/antenna/antenna.html

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Offline DaleReid

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #2 on: December 06, 2017, 07:26:11 PM »
This one has a long (1/4 wave) antenna hanging down out of the bottom of the weather resistant enclosure.  Darn.
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Offline WVZR-1

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #3 on: December 27, 2017, 07:15:08 PM »
I could get excited about an antenna improvement myself. I do believe that Richie did have me change mine when we did the install. Mine is a Mark III from maybe '05 that was shelved for many years and I bought NOS in maybe '14 or '15.

Offline miraculon

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #4 on: December 28, 2017, 09:22:13 AM »
With my Davis long-range repeater, I used a mini-circuits LNA. My particular model doesn't cover the 418MHz frequency, but I found a model on eBay that does: Mini-Circuits-ZFL-500HLN


It will give you 19dB of gain.

Also, I was able to extend the range of my garage door opener with a Ham 70cm yagi. The GDO was a bit lower on frequency, but apparently the antenna had enough bandwidth to help.

I modified the PCB where the wire antenna came from to add a SMA female socket. Then I ran a SMA male to a N-connector at the antenna. If you get the amplifier inline, you would need a SMA-SMA jumper cable. The only issue that I see is that the mini-circuits amp draws 110mA. If you could get power to where the Mark III is, this could work. (I feed 15VDC from the garage up the mast to the repeater pre-amp). I also have a 902-928MHz passive filter in line to eliminate some local interference. I don't know if you could find a similar BPF for 418MHz.

Otherwise, maybe a substantial solar/battery rig could run the preamp.

Greg H.


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Offline DaleReid

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #5 on: December 28, 2017, 01:14:11 PM »
Thanks, there is always more than one way to skin the proverbial cat. 

I would like a simple gain antenna solution for this install, but this is an idea for the future.
Dale
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Offline WA7FWF

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #6 on: January 01, 2018, 11:49:46 AM »
No idea how much they cost but yagi's are available. maybe one out at the sender with a short sma to N coax. http://elcodis.com/parts/1967858/ANT-418-YG5-N.html or you could probably build your own by looking over some DIY ham 440mhz designs and scaling it for 418 or I found a site for building your own you might want to look at http://radio.meteor.free.fr/us/antenna.html

Offline DaleReid

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Re: increasing range of 418Mhz Mark III with antenna mods?
« Reply #7 on: January 01, 2018, 12:31:10 PM »
Thanks, I'll look again at the link.  The schematic looks straightforward enough.  This summer I built a coaxial receive for the FlightRadar24 frequency out of some brass tube that I found with some brazing rod and it was much more fun of a project than twising wire and using coax cable that most of the on line projects used.

I can figure out the lengths and cut them much more accurately, too.

The only thing I'll need to see is how to connect it to the output of the RainWise transmitter board.  I think this is sort of an end fed dipole wire hanging out, so I'd have to see if the impedance matche would be OK if I tried putting a 1/2 wave length of coax on and grounded the shield to the nearest ground on the board.

I've seen many of the little pump stations and some river monitor stations (which seem to be aimed at a satellite for relay) but the pumping or lift station yagis seem to be aimed back to some tower around town.  They wouldn't go to the trouble if it didn't help is my guess.

Thanks to all again for the ongoing help.  Not being a radio engineer and understanding the intricacies is a problem.
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