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How much salt is there in quality coax?

dazmatic

ULTIMATE Member
Recently picked up a couple of these antenna feeds and so they look ok. VSWR is a little higher than I'd like but to be expected considering they're wide band LPDA in a small package. I've got one installed on a grid dish - vertical - it really looks the part but I think a +/-45° angle would be better.

However, the RSRP compared to my iskra is slightly less (angle?) and the upload speed is also. The SINR though is awesome, from 7 to 17, now that's brilliant and has a clear effect on downlink. I get about 97/98 RSRP on band 3, 5 miles from mast so I'm already really pushing the limits of what's possible.

There's one thing that's bothering me though, the cable.
I took down the other feed because after a couple of weeks, VSWR went sky high and became useless. I now think it was actually the cable or the connectors more to the point, I'll check the old feed when I get round to it. I also don't think I did a good job wrapping the connector.

It's LMR200 cable and I suspect it's too long for the frequency, approx 8/9 meters.

I think I might need better cable, but don't want to break the bank.

1. Is it worth swapping out the coax?
2. If so, what's the best bang for buck cable?
3. Is there much difference between +/-90° and +/-45° polarisations for antenna?
 
Can you jump to LMR-400 cable (definitely an ultraflex variety)? 9 metres is a fair distance.

I buy a fair chunk of my coax assemblies through Gigatronix or straight cable via one of the wholesalers.
 
Salt? what are you planning to do with this Coax, eating it with Chips 😁

LMR400 is a good upgrade over 200 Cable but I would always recommend original Times Microwave (you get what you pay for) over cheaper cloned copies, in my trade as an RF and Radio Comms Engineer when TM LMR first came out, we called it the Poor Man's LDF (Andrews or Cell flex Heliax) but the proper LMR does perform well, and like you say a good quality Connector is key in any Installation, it's all about stopping the water and moisture getting in.

I have always wrapped my Connectors with a Triple layer of Almagamating Tape and then Triple wrapped with PVC Tape (keep the PVC warm in your pocket, then slightly stretch it without breaking it during the wraps).

Slightly off topic, with LMR400 and any decent Heliax Cable with the right Connectors you can pressurise the Cable with either Helium or a Controlled Air Pump with just enough over normal Atmospheric pressure to keep out Moisture, Water and Freezing Ice, done this a few times on Sea going Yatch and Boat Installs or Outdoor Routers via the Coax feed, but that's another story.
 
Last edited:
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Recently picked up a couple of these antenna feeds and so they look ok. VSWR is a little higher than I'd like but to be expected considering they're wide band LPDA in a small package. I've got one installed on a grid dish - vertical - it really looks the part but I think a +/-45° angle would be better.

However, the RSRP compared to my iskra is slightly less (angle?) and the upload speed is also. The SINR though is awesome, from 7 to 17, now that's brilliant and has a clear effect on downlink. I get about 97/98 RSRP on band 3, 5 miles from mast so I'm already really pushing the limits of what's possible.

There's one thing that's bothering me though, the cable.
I took down the other feed because after a couple of weeks, VSWR went sky high and became useless. I now think it was actually the cable or the connectors more to the point, I'll check the old feed when I get round to it. I also don't think I did a good job wrapping the connector.

It's LMR200 cable and I suspect it's too long for the frequency, approx 8/9 meters.

I think I might need better cable, but don't want to break the bank.

1. Is it worth swapping out the coax?
2. If so, what's the best bang for buck cable?
3. Is there much difference between +/-90° and +/-45° polarisations for antenna?
I bought some hdf400 from these guys, about £1.3/m, so quite affordable for say 10m length(they do custom lengths).

 
Can you jump to LMR-400 cable (definitely an ultraflex variety)? 9 metres is a fair distance.
Is 9 meters far? It's the difference that much?

We're talking fringe here so there's not a lot to work with in the first place.
 
Is 9 meters far? It's the difference that much?

We're talking fringe here so there's not a lot to work with in the first place.
I would say if you’re in fringe then every dB loss counts. You can make your own educated decision based on loss tables for each coax type at given frequency.

Personally I don’t see the point going to the trouble if fitting a high gain antenna but then losing most of that gain in the connecting cable etc. 3dB is a doubling (or halving) of signal strength.
 
Salt? what are you planning to do with this Coax, eating it with Chips 😁
I like my internet well seasoned

LMR400 is a good upgrade over 200 Cable but I would always recommend original Times Microwave (you get what you pay for) over cheaper cheaper copies, in my trade as an RF and Radio Comms Engineer when TM LMR first came out, we called it the Poor Man's LDF (Andrews or Cell flex Heliax) but it the proper LMR does perform well, and like you say a good quality Connector is key in any Installation, it's all about stopping the water and moisture getting in.
I'm not exactly poor, but neither am I wealthy and I've sunk hundreds (sic Thousands?) Into this already, so much so it's practically a hobby. I'm aware LMR400 is expensive, is there something  almost as good but kinder to the purse strings?

I have always wrapped my Connectors with a Triple layer of Almagamating Tape and then Triple wrapped with PVC Tape (keep the PVC warm in your pocket, then slightly stretch it without breaking it during the wraps).
Yeah, so I've done self amalgamating tape, but what I didn't know is how much. Judging by what you do, mine was naught but a token gesture 😅 done 2 full wraps this time though but probably need pvc
 
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I bought some hdf400 from these guys, about £1.3/m, so quite affordable for say 10m length(they do custom lengths).

That's interesting, I think I've got 11mm jaws on my crimp, if I could make my own cable that'd be better. Was the cable good quality?

Did you get terminals from there too?
 
Salt? what are you planning to do with this Coax, eating it with Chips 😁

LMR400 is a good upgrade over 200 Cable but I would always recommend original Times Microwave (you get what you pay for) over cheaper cheaper copies, in my trade as an RF and Radio Comms Engineer when TM LMR first came out, we called it the Poor Man's LDF (Andrews or Cell flex Heliax) but it the proper LMR does perform well, and like you say a good quality Connector is key in any Installation, it's all about stopping the water and moisture getting in.

I have always wrapped my Connectors with a Triple layer of Almagamating Tape and then Triple wrapped with PVC Tape (keep the PVC warm in your pocket, then slightly stretch it without breaking it during the wraps).

Slightly off topic, with LMR400 and any decent Heliax Cable with the right Connectors you can pressurise the Cable with either Helium or a Controlled Air Pump with just enough over normal Atmospheric pressure to keep out Moisture, Water and Freezing Ice, done this a few times on Sea going Yatch and Boat Installs or Outdoor Routers via the Coax feed, but that's another story.
I like / use PPC connectors. There’s a lot of good stuff that’s come from the American cable TV and radio industry.
 
Can you jump to LMR-400 cable (definitely an ultraflex variety)? 9 metres is a fair distance.
So, looking at some charts, at 2Ghz and 10 meters LMR200 loss is 4.9dB, LMR400 is 2.3dB and the HDF400 linked above is 1.96dB

So there's a gain of 3dB to be had by changing the cable. In real world terms, what does that look like in terms of signal strength?
 
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Yes. I'm aware it's a 3dB gain.

But in terms of signal stats, should I see a doubling of received power for example?
 
But in terms of signal stats, should I see a doubling of received power for example?
Well, yes. if your current signal level is -97dBm, then you should get -94dBM if you swap the cable for one that has 3dB less attenuation.
The SINR should increase by 3dB as well (which I consider more important than RSRP.

Looking at the data sheets, there is hardly any difference between the LMR-400 and the HDF-400, however, the HDF-400 seems tp cost a lot less than the LMR-400.
 
That's interesting, I think I've got 11mm jaws on my crimp, if I could make my own cable that'd be better. Was the cable good quality?

Did you get terminals from there too?
Yes, got terminals, too. Quality seems good, it's proper cable, the core is copper coated aluminium.
 
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Well, yes. if your current signal level is -97dBm, then you should get -94dBM if you swap the cable for one that has 3dB less attenuation.
The SINR should increase by 3dB as well (which I consider more important than RSRP.

Looking at the data sheets, there is hardly any difference between the LMR-400 and the HDF-400, however, the HDF-400 seems tp cost a lot less than the LMR-400.
I was actually going to type a similar response, but was too lazy. 🤣

How wieldy do you find 400 - tis about the same size as RG11 for TV/Sat stuff which can be a right ******* to get around stuff. I prefer stranded conductor (ultra flex) at this size for this reason.
 
400 is as thick as my index finger, they say you should allow 10cm for a turn, to avoid damage.
 
Looking at the data sheets, there is hardly any difference between the LMR-400 and the HDF-400, however, the HDF-400 seems tp cost a lot less than the LMR-400.
With lmr you seem to be paying a bit extra for the "brand" .. Hdf is extremely similar implementation.
 
Is 9 meters far? It's the difference that much?

We're talking fringe here so there's not a lot to work with in the first place.

It was too far for me even with the extra gain from the parabolic reflector. I ended up ditching cables altogether and mounting the whole router on the end of the feed prong.

Edit: I tried to add a picture but it isn’t working today.

I’m now working on a quick release mount to fit an SXT on the end of the feed prong. Hope to test in situ next week.
 
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