Difference in ability to TX and RX on base station

[Whiskey363]

10 minutes ago, Raybestos said:

  To be honest, at 3db loss, if you hear it you should be able to hit it, which brings us back to my theory that you may be in a good spot to hear it on 462, but an absolute null at 467.  I know it is probably the last thing you want to do, but I would go on the roof and move the antenna a foot or so sideways and or forward and backward.  To prevent additional such trips, have your wife or other trusted person in your radio room, ready to try and key up the repeater at your direction.  If possible, back away from the antenna when they do so to minimize body capacitance and other possible weirdness which might change once you are back on the ground.

This brings another thought.  Can you hit the repeater with the 935G from inside your home or outside?  If so, it is very likely a null you are dealing with.

 

 

https://messi.it/en/comparison-chart--attenuationpower-ratio.htm

 

 

I don't have any options moving it forward or backward. I tried moving it 6 inches to the left and then right, but haven't noticed a difference. Maybe it needs more as you are suggesting, like a foot at a time. 

I can't hit the repeater on the 935. 

I don't know if this matters but when I key up on 462 I only have about 1.2 SWR, but on 467 it is 1.8. 

[Raybestos]

The 1.8 SWR, while not ideal, shouldn't hurt you too badly, unless the KG1000 has an "RF fold back for higher SWR".  Some VHF and UHF ham radios are so sensitive on RF foldback,  they reduce power significantly with SWR as low as 1.5:1.  

[Whiskey363]

I have a 50 foot section of Messi & Paoloni Ultraflex 7 Premium coax, and a 25 foot section that goes from the lighting arrestor to the antenna. Would it make any significant difference to replace the 50 foot section with a 50 foot section of Browning BR-400 Low Loss RF coax? I am overall pleased with my setup, can RX from 15 miles away with hilly terrain and woods. I would just like to boost my TX ability. I can send clearly 5 miles apart line of sight with my family, so my equipment appears to be in good working order, would just like to boost TX distance. 

[SteveShannon]

3 minutes ago, Whiskey363 said:

I have a 50 foot section of Messi & Paoloni Ultraflex 7 Premium coax, and a 25 foot section that goes from the lighting arrestor to the antenna. Would it make any significant difference to replace the 50 foot section with a 50 foot section of Browning BR-400 Low Loss RF coax? I am overall pleased with my setup, can RX from 15 miles away with hilly terrain and woods. I would just like to boost my TX ability. I can send clearly 5 miles apart line of sight with my family, so my equipment appears to be in good working order, would just like to boost TX distance. 

M&P Ultraflex 7 isn’t really optimal for UHF, but I don’t know what the quality is of the BR-400.  The name would imply a diameter of 0.40 inches, making it the same diameter as LMR400, but I don’t know if it as good as LMR400 or one of the 10 mm M&P cables for UHF. Going to M&P 10mm cable (hyperflex, Ultraflex, or broadpro) would make a difference in the power that reaches your antenna, but more power doesn’t always mean greater distance.  It usually improves the clarity of the signal though. Honestly, if you’re happy I would just leave it alone until for some reason you aren’t.

There are many posts that provide a coax loss calculator, try running the calculations to see whether you think it’s worth it or not.

[Whiskey363]

Steve,

   Thank you for your reply. The problem with the coax loss calculators for the uninitiated is they are not listed as you would purchase it. There is no option for Ultraflex 7 or 10. There is RG, LMR, etc, but I can't figure out which to select. 

[SteveShannon]

15 minutes ago, Whiskey363 said:

Steve,

   Thank you for your reply. The problem with the coax loss calculators for the uninitiated is they are not listed as you would purchase it. There is no option for Ultraflex 7 or 10. There is RG, LMR, etc, but I can't figure out which to select. 

For UF7 choose lmr240.  For uf10 choose lmr400.  That’s not exact, but it’s very close.

[Whiskey363]

Thank you, very helpful!

[Whiskey363]

LMR 240 that I currently have has me at 4.36dB loss or 22 percent more power loss than LMR 400. Seems pretty significant to me.

[GMRSJohn]

LMR400 is pretty good stuff.

[AdmiralCochrane]

Unless your current coax is making significant loss, changing to lower loss coax isn't going to make a difference in your TX distance.  Elevation is the place to spend your money.  (Fars and moneys in Randyspeak. I don't know the proper Randyspeak term for elevation; might be highs, talls or ups.) 

[Whiskey363]

30 minutes ago, AdmiralCochrane said:

Unless your current coax is making significant loss, changing to lower loss coax isn't going to make a difference in your TX distance.  Elevation is the place to spend your money.  (Fars and moneys in Randyspeak. I don't know the proper Randyspeak term for elevation; might be highs, talls or ups.) 

I guess it depends on your definition of significant loss, but the calculator has it at a 63% power loss, which I take as significant. I absolutely agree that height is might, and I have the antenna a total of 15 feet above my roof line, which is as high as feel acceptable for the neighborhood. 

I could be way of base, but the fact that I can clearly RX transmissions from repeaters 15 miles away, tells my antenna is high enough. From my small knowledge base and experimentation, it is the power loss in my coax that is preventing me from TX to the repeater. Could be totally wrong, but It won't be to much of a hassle to swap it out. 

[AdmiralCochrane]

An accurate test.  Let us know the result.

[Whiskey363]

Going to take me a few weeks, but I will most certainly report the results!

[SteveShannon]

Swapping in better coax certainly won’t hurt. I agree that a 63% power loss is substantial. What’s the projected power loss after swapping?  

[Whiskey363]

41% with 75 feet of LMR-400. That's with bumping the Load SWR from 1.5 to 1.8. That is what I currently have, so I'm keeping it constant. I'm also considering switching from UHF to Type N Connectors. 

[LeoG]

20 hours ago, Whiskey363 said:

Steve,

   Thank you for your reply. The problem with the coax loss calculators for the uninitiated is they are not listed as you would purchase it. There is no option for Ultraflex 7 or 10. There is RG, LMR, etc, but I can't figure out which to select. 

M&P have their own calculator, it's not sophisticated though.  But you can take that number and plug it into the other calculators to see the results.

[SteveShannon]

14 hours ago, Whiskey363 said:

Going to take me a few weeks, but I will most certainly report the results!

One thing to be aware of is that SWR will appear to go up, possibly by quite a bit. Here’s why:

SWR is calculated using forward transmitted power and reflected power.  At your radio the forward transmitted power is the maximum.  Attenuation in your cable reduces it as it travels along the cable until it finally arrives at the antenna. There, any mismatch in impedance causes a portion of the power to be reflected back towards your radio.  Again, attenuation robs power from the reflected power as it travels back towards your antenna. Your radio or a SWR/wattmeter measures the forward and reflected power wherever it’s inserted into the feedline. So, any power measurement done at the radio will measure the lowest possible reflected power and utmost forward power, which results in a calculation of SWR that’s not accurate.  
Let me emphasize that the actual SWR of the antenna doesn’t change, but because forward and reflected power are being measured at the radio, the calculated value of SWR is incorrect.
Replacing the lossy 7 mm cable with less lossy 10 mm cable will result in less attenuation both ways which will result in a higher (but more nearly accurate) calculation of SWR.  
Of course the most accurate place to measure power is right at the feedpoint of the antenna, where the actual forward power delivered to the antenna and the actual power reflected by the antenna can be measured most accurately, but it’s almost always inconvenient to do so.

[Whiskey363]

24 minutes ago, LeoG said:

M&P have their own calculator, it's not sophisticated though.  But you can take that number and plug it into the other calculators to see the results.

I did not see that calculator, thank you.

[Whiskey363]

4 minutes ago, SteveShannon said:

One thing to be aware of is that SWR will go up, possibly by quite a bit. 

That is something I was completely unaware of. Thank you for informing me of that. At 1.8 I really can't afford for it to be any higher. Would you recommend I do not upgrade the coax? I was under the assumption this would lower the SWR as well. Thank you for your excellent, easy to understand explanation. 

[SteveShannon]

5 minutes ago, Whiskey363 said:

That is something I was completely unaware of. Thank you for informing me of that. At 1.8 I really can't afford for it to be any higher. Would you recommend I do not upgrade the coax? I was under the assumption this would lower the SWR as well. Thank you for your excellent, easy to understand explanation. 

I’ll correct my explanation to emphasize that the SWR is not actually going up, your measurement of reflected power is becoming more accurate.  As a result the SWR value calculated at your radio will become higher, but in reality it has been the actual SWR hasn’t changed. You’re just seeing a more nearly accurate calculation.  
In other words, your SWR is higher than what you’re seeing and changing to the better cable will reveal that.

[SteveShannon]

18 minutes ago, Whiskey363 said:

At 1.8 I really can't afford for it to be any higher. Would you recommend I do not upgrade the coax? I was under the assumption this would lower the SWR as well. Thank you for your excellent, easy to understand explanation. 

So the actual SWR of the antenna is almost certainly already higher than 1.8.  
No, I wouldn’t recommend not upgrading the coax.  Lossy coax simply hides high SWR.

The “right” thing to do depends on your resources.  I would measure the SWR of the antenna right at the antenna feedpoint and adjust the antenna (tune it) until it’s as close to 1.0:1 as possible at the frequency you intend to transmit most often.  I’ll have to go back and see what antenna you’re using and whether it’s one that can be tuned.

Then, your reflected power will be reduced to the minimum and the attenuation of reflected power will have no effect on the apparent SWR.

[Whiskey363]

9 minutes ago, SteveShannon said:

I’ll correct my explanation to emphasize that the SWR is not actually going up, your measurement of reflected power is becoming more accurate.  As a result the SWR value calculated at your radio will become higher, but in reality it has been the actual SWR hasn’t changed. You’re just seeing a more nearly accurate calculation.  
In other words, your SWR is higher than what you’re seeing and changing to the better cable will reveal that.

Steve,

  With that being said what would you estimate the actual SWR reading is? From my understanding anything over 2 can damage the radio. Or is the incorrect SWR reading at the base of the radio taken into account with the 2 or lower number?

[Whiskey363]

I'm using the Tram 1486, but was thinking of switching to the Comet CA-712EFC 460-470MHz 9 dBi Gain Base/Repeater Antenna when they come back in stock. 

[Whiskey363]

Headed to work, but thank you for your insight.  Will certainly continue to research before I pull the trigger on the final coax and antenna. 

[LeoG]

22 minutes ago, Whiskey363 said:

I'm using the Tram 1486, but was thinking of switching to the Comet CA-712EFC 460-470MHz 9 dBi Gain Base/Repeater Antenna when they come back in stock. 

This is where I got mine.  And the paperwork says 9.8dBi gain.