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Chinese parabolic grid dish antenna

dazmatic

ULTIMATE Member
Afternoon everyone.

I'm after a little advice regarding antennas and their failure modes.

I have 3 antennas mounted outside about the eaves of my bungalow, pictures of antennas attached. One is a chinese made grid antenna tuned for B3/B1/N78 frequencies and the other is a pair of Iskra P60 LPDA antennas.

I'm using Three and connecting to Band3 4G primary. With the Iskra antennas, I get around 98dBm on a good day with the antennas being around 10.5dB of gain at 1800mhz. This is 5 miles-ish from the mast so pretty good antennas as far as I'm concerned.

I wanted more however and got the chinese grid dish antenna for 1800mhz with a reported gain of 24db+. Obviously, to expect 24dB from a chinese antenna is unrealistic however I would expect 17/18dB at least with the dish.

Initially, when I installed the dish I was getting 92-94dBm of received power so an increase over the Iskra and have continued to use since. Past few months however, received power levels have dropped on the chinese grid dish to upwards of 108dBm and subsequently I've changed back to the Iskra which is currently floating around 97-100dBm.

Nothing has changed, nothing has moved, cabling is fine. My question, what else could have caused the received power to drop like this? Is it just poor quality antenna?

Point to make, this has happened after weather events - high winds etc but the position of the antenna hasn't moved so could be coincidence?

I don't want to pull the mast down and remove the dish to check but it's it's pretty useless I may well.

Just interested to see what the thoughts could be on this.

Thanks all
 

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Afternoon everyone.

I'm after a little advice regarding antennas and their failure modes.

I have 3 antennas mounted outside about the eaves of my bungalow, pictures of antennas attached. One is a chinese made grid antenna tuned for B3/B1/N78 frequencies and the other is a pair of Iskra P60 LPDA antennas.

I'm using Three and connecting to Band3 4G primary. With the Iskra antennas, I get around 98dBm on a good day with the antennas being around 10.5dB of gain at 1800mhz. This is 5 miles-ish from the mast so pretty good antennas as far as I'm concerned.

I wanted more however and got the chinese grid dish antenna for 1800mhz with a reported gain of 24db+. Obviously, to expect 24dB from a chinese antenna is unrealistic however I would expect 17/18dB at least with the dish.

Initially, when I installed the dish I was getting 92-94dBm of received power so an increase over the Iskra and have continued to use since. Past few months however, received power levels have dropped on the chinese grid dish to upwards of 108dBm and subsequently I've changed back to the Iskra which is currently floating around 97-100dBm.

Nothing has changed, nothing has moved, cabling is fine. My question, what else could have caused the received power to drop like this? Is it just poor quality antenna?

Point to make, this has happened after weather events - high winds etc but the position of the antenna hasn't moved so could be coincidence?

I don't want to pull the mast down and remove the dish to check but it's it's pretty useless I may well.

Just interested to see what the thoughts could be on this.

Thanks all
It sounds like water ingress to me, either in the casing or/and in the coax. All else being unchanged, I can't think of a different reason...
 
Ann
It sounds like water ingress to me, either in the casing or/and in the coax. All else being unchanged, I can't think of a different reason...
Annoyingly, I think your right. The coax connectors have been wrapped in self amalgamating tape but the feed horn is sealed tight. Wouldn't be surprised if there was condensation or corrosion.
 
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I notice the same thing happen with my Poynting LPDA-92's ,they definitely do get affected by water over time although they are by far the best antenna I've used , I get -98 RSRP on B1 with a 12m run of cable and -96 RSRP on B3 and I'm 16km away with line of sight as I'm up high on a mountain. It's a couple dB better when I use the original 7m cable that comes with them but if you could reduce the cable run further I'd recommend those.

Mine still holding up pretty good , one of them had dropped off similar to your's and I sucked the water out of the cable and it magically went back to normal again. Bit of a silly way of doing it but it did work 😅 sealed it up again best I could and still been working ever since.
 
I use a metre dish like that for Three although I use a B310 as a feed. One day the signal just dropped and it has never come back.

I assumed that it was something that Three had done at the mast.
 
I notice the same thing happen with my Poynting LPDA-92's ,they definitely do get affected by water over time although they are by far the best antenna I've used , I get -98 RSRP on B1 with a 12m run of cable and -96 RSRP on B3 and I'm 16km away with line of sight as I'm up high on a mountain. It's a couple dB better when I use the original 7m cable that comes with them but if you could reduce the cable run further I'd recommend those.

Mine still holding up pretty good , one of them had dropped off similar to your's and I sucked the water out of the cable and it magically went back to normal again. Bit of a silly way of doing it but it did work 😅 sealed it up again best I could and still been working ever since.
BTW, are you using low loss cable for that? Like HDF400 or CLF200? I know you are to move the router close to the antennas soon and it won't matter, but just curious.
 
BTW, are you using low loss cable for that? Like HDF400 or CLF200? I know you are to move the router close to the antennas soon and it won't matter, but just curious.
It's just the original cable that comes with it so it's HDF195. I been having a rough time getting the router itself to behave properly though, very strange behavior with antenna ports. I can get LPDA-92 to connect to B28,B3,B1,N78 only if I have them in port 4+2 going by PCB markings. And if I have 4 antennas hooked up it won't connect to that combo at all LTE-A only. And then if I put the XPOL V3 in the same 2 ports as the LPDA's, it won't even connect in that combo despite it having better N78 signal. Only way I have it working is , LPDA in 4+2 first, then once connection established, N78 signal goes from -126 to -110 RSRP when I plug in XPOL in the other two 1+3 ports but ONLY works but doing that sequence. I'm hoping it's some signal threshold level to establish connection as the xpol is about 1-3 dB weaker than the LPDA's. No point hooking it up in the EPNT-2 if I have to disassemble enclosure and connect antennas in certain sequence just to initialise the combo I want 🤣
 
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If the weather is nice this weekend I'll pull out down and investigate. It's pretty much useless at the minute if it's worse than the Iskras and I've got another pair of Iskra or Bluespot or panorama WMM8G to chuck up instead
 
Just remembered, I've got a VNA, might chuck that on and check if there's anything wrong - not that I know what I'm doing with it mind 🤣
 
Just remembered, I've got a VNA, might chuck that on and check if there's anything wrong - not that I know what I'm doing with it mind 🤣
Yeah, if you have one is great, pick a frequency that's supported and check the vswr, maybe against the data sheet that came with the antenna if there's such a thing.
 
So I'm going to necro this thread albeit it's not too old.

I took down the dish last weekend and managed to get it opened today.

It's not great quality and compared to others I've seen (c/o Andrew McNeil) this is a rip-off version and doesn't have a proper feed. Definitely not great and could do with improvements (ideas?)

As far as the fault goes? I'm not sure - I can not see anything physically wrong with it and it's sealed tight (apart from no grommets for the cable entry)

However, the VSWR for the B3 frequency is higher than I would expect? (see next post)

Also something of note worthy relevance, this feed horn has both horizontal and vertical polarisation and the arrow aligns with the horizontal. Because the dish is missing the top and bottom half (essentially not a full parabolic reflector) gains on the vertical polarisation were considerably less than horizontal. I suspect, if I were to rotate the feed 45 degrees to the dish, the gains would be even across both polarisations although slightly less than horizontal - the gain would be worth it.

IMG_20221118_180132-scaled.jpg

IMG_20221118_180148-scaled.jpg
IMG_20221118_180208-scaled.jpg
 
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As you can see from the below image, B3 has a low-ish VSWR in the middle, however this goes over 2.0 in the bottom and top end of B3 but still acceptable considering it's to be used with a dish.

However, because I've got nothing to compare to at the minute, there's nothing to explain why performance dropped other than it being a crappy feed.

Middle-ish of B32
IMG_20221118_201332-scaled.jpg


Middle of B3
IMG_20221118_201310-scaled.jpg


Middle-ish B1
IMG_20221118_201248-scaled.jpg


Bottom of N78 band
IMG_20221118_201218-scaled.jpg


Middle of N78 band
IMG_20221118_201154-scaled.jpg


Top of N78 band
IMG_20221118_201142-scaled.jpg
 
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