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 Post subject: Re: Antenna Systems 101
PostPosted: Sat May 16, 2015 1:21 am 
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Posts: 75
that is what it measures in 52.525 mhz appx 1/4 mi away.
On my Honda CRV the cowl mount comes up from alongside the hood, drivers side.
There are a few inches of body fender metal further left for counterpoise.
On friends Nissan, there is really no "horizontal" body fender metal to the left of the coil base.
I kinda expected 3 or 4 dB nulls as you "rotate" the truck.
I am using a Larson NM050, the other is an Antennex.


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 Post subject: Re: Antenna Systems 101
PostPosted: Sun Jun 28, 2015 12:52 pm 
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Location: Puget Sound
http://www.repeater-builder.com/tech-info/db.html


I actually might have time to get back to this one of these days.

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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Jul 04, 2016 10:24 am 
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Location: Puget Sound
Ive been doing some research on LMR240 and found a cable kit premade with the stuff which I have purchased. Because I think John is using the best cable that could be used in these circumstances. And I need a super low loss cable for a project.

According to the charts 8x and LMR240 are the same diameters (use the same connectors) which makes things much easier. LMR240 shows lower loss numbers than 8X (Laird) and as mentioned in this thread earlier 8X numbers tend to be all over the place.

Im going to do a final "coverage" test for this thread. Using my X100DR microphone Im going to test with the ATX195 Laird cable kit I have installed now and change it out to the 240 cable kit and do a walk test. The port on the X10DR is a reverse gender female SMR and took me some looking to find the males for 8X/LMR240. (about $8 a piece.)

The X10DR works on 2.4ghz and is rated at 100mw. The antenna is a Laird 2.4ghz TRA24003.


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More to come.

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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Jul 04, 2016 1:06 pm 
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Location: Puget Sound
Preliminary results- Keep in mind- its only 100mw.

ATX195 181 yards

LMR240 194 yards

Not the 300 meters the X10DR people advertise but I believe I need their optional BDA to make that happen.

Got some more comparisons to make..

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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Jul 04, 2016 5:57 pm 
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chpalmer wrote:
Not the 300 meters the X10DR people advertise but I believe I need their optional BDA to make that happen.


I think that 300m number is probably based upon some fancy math versus real-world performance.


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 Post subject: Re: Antenna Systems 101
PostPosted: Sun Jul 31, 2016 2:42 pm 
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Finally unloaded my camera- Here is the LRM240 and reverse gender SMA connector.


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 Post subject: Re: Antenna Systems 101
PostPosted: Fri Aug 05, 2016 12:27 am 
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Location: Puget Sound
Standard VHF (high band) portable antenna gain.. Minus 10dB

RF noise floor measured at most of our repeater sites.. 6bB

Or in layman's terms- about 0.15 watt ERP from your 5 watt portable.

Yes I over simplified it. But now you know why so many portable transmissions suck!

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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Aug 08, 2016 7:28 pm 
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Have you experimented with putting extra pass cans in the RX line at the site? While you may have 2 dB of ins loss, if it gets you 4 dB the you're 2 dB ahead.

6 dB is pretty good. I can tell you from experience, 3 dB is noticeable. Someone once told me, a dB is a dB. Lol

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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Aug 08, 2016 10:30 pm 
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Location: Puget Sound
jrw14493 wrote:
Have you experimented with putting extra pass cans in the RX line at the site? While you may have 2 dB of ins loss, if it gets you 4 dB the you're 2 dB ahead.

6 dB is pretty good. I can tell you from experience, 3 dB is noticeable. Someone once told me, a dB is a dB. Lol


The site noise is wideband and covers our frequencies. Cans just keep the adjacent channel stuff down. And yep- full bandpass cans everywhere.

Ive got a few sites with crystal filters that do one hell of a job with the adjacents but we still see around 6dB.

Im seeing 25dB right now at my house on my lowband stuff.

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 Post subject: Re: Antenna Systems 101
PostPosted: Tue Aug 09, 2016 10:47 am 
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Yep. That's the problem with using pass cans. Wideband on freq. stuff sails right through. It's nice to use them to knock down the off freq stuff which can help. (Thinking of a site where PP&L has a MPT1327 control channel TX'er at what must be 100 gigawatts -- just killing a poor VHF repeater 1000' away. Their freq. is 161.925 ((another topic for another thread)) and I'm trying to receive at 157.4925. Pass can took like 15 dB of noise down to 5.)

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 Post subject: Re: Antenna Systems 101
PostPosted: Tue Aug 09, 2016 12:26 pm 
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Location: Puget Sound
jrw14493 wrote:
Their freq. is 161.925 ((another topic for another thread)) and I'm trying to receive at 157.4925. Pass can took like 15 dB of noise down to 5.)


I bet if you could talk them into installing a notch filter on their transmitter with your receive frequency notched out you could knock that down even further.. What kind of receiver are you using? Have a mechanical preselector on it?

But truthfully 5dB is less than the ambient site noise I see all over the place right now. So I guess you be doing good!

Got any lowband receivers you could test for me?? :)

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 Post subject: Re: Antenna Systems 101
PostPosted: Sun Oct 09, 2016 9:06 pm 
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Location: Puget Sound
Found some NMO mounts with FME sockets on them. Makes use of LMR240 without soldering and full 100% shielded at the base of the antenna. Only thing I don't like it the nickel center contact. Older mounts we used to have where brass but appear to be out of production. I had one left and put it on my van. (Im selfish like that)

800mhz Customer we did these for can now talk through (rough copy) the repeater in places where the original RG58 install couldn't even tickle the repeater receiver before. Receive on the mobile of coarse is also a pretty dramatic improvement.

But everyone knows it's more profitable to just tell the customer build more repeater sites I guess.


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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Oct 10, 2016 2:06 pm 
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Interesting combination, maybe I will give that a try on the truck. I thought FME's were similar to PL259's when it comes to performance shortcomings on UHF and above. Either way (at 800mhz) you are probably picking up 1-1.5db with the better cable and another 1-1.5db with the correct connection/shielding at the mount base.


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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Oct 10, 2016 4:18 pm 
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Rich wrote:
Interesting combination, maybe I will give that a try on the truck. I thought FME's were similar to PL259's when it comes to performance shortcomings on UHF and above. Either way (at 800mhz) you are probably picking up 1-1.5db with the better cable and another 1-1.5db with the correct connection/shielding at the mount base.


Good point- Im not sure myself about FME loss but know the antenna companies tend to use the connector on their cellular offerings so I kinda went by their lead there.. I did one of the installs with an SMA NMO mount so have the ability to test that if I needed to. And now I'm intrigued!

From the Times Microwave Cable Calculator.. 17feet at 810mc
Cable Assembly Performance LMR240
Cable Run Attenuation: 1.2 dB
Total Cable Assembly Loss: 1.4 dB
Cable Run Efficiency: 75.6 %
Cable Run Time Delay: 20.56 nSec

Cable Assembly Performance RG-58
Cable Run Attenuation: 2.3 dB
Total Cable Assembly Loss: 2.4 dB
Cable Run Efficiency: 58.6 %
Cable Run Time Delay: 26.17 nSec

So according to their calculator only 1db.. But almost 20% more efficient.. And with other factors such as going from big button to small button.. 100% shielding like you mention, and I used a Laird B7603 5/8~ antenna to replace the center "curly" coil wire antennas. Just trying to take out the weak links out of the antenna system.

I think if nothing else this is a good post to point all the guys that complain that they can't hear the next counties 800 system with their 100 feet of rg-58 that they ran up a tree to their antenna of choice. :)

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 Post subject: Re: Antenna Systems 101
PostPosted: Mon Oct 10, 2016 6:44 pm 
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chpalmer wrote:
I think if nothing else this is a good post to point all the guys that complain that they can't hear the next counties 800 system with their 100 feet of rg-58 that they ran up a tree to their antenna of choice. :)


Reminds me of a situation I dealt with a number of years ago. A prominent DoD contractor spec'd and installed a mobile data system for a fairly good sized western WA LE agency and couldn't figure out why it wouldn't work. I was invited to look it over and found between the cable type, cable length, improper mount feed, and low-band button their calculated transmit loss was about 150% of the signal by the time it reached the antenna.

And to put more salt in the wound the (short non-elevated) antenna was 100% obstructed to the front by the light bar.

The lesson I learned that day is some stuff is so stupid you couldn't make it up if you tried.


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