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calculating PHG

 
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NG9R  



Joined: 11 Jul 2005
Posts: 5
Location: Camp Point, IL

PostPosted: Fri Jul 15, 2005 8:57 am    Post subject: calculating PHG Reply with quote

I have a question for those that have digis with fairly high HAAT. Do you calculate the feedline loss into your power factor? We have 3.6 dB loss in the feedline to our anyenna at 320', so I am assuming I would subtract the feedline loss from the actual transmitter output power for range circle calulations. Am I wrong in this thinking?

NG9R
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Robbie  



Joined: 02 Jul 2004
Posts: 32
Location: Buffalo Grove, IL

PostPosted: Fri Jul 15, 2005 4:35 pm    Post subject: calculating PHG Reply with quote

Hi Dan,

I would say yes if you don't know for sure your real coverage from tests.. You can have a very low PHG but yet your location would tend to give you better coverage than avertised, Smile and the reverse could also be true..

My thoughts would be to run it as close to what you think is reasonable, then as time goes by and you have reports to substantuate your signal one way or another, feel free to adjust accordingly.. Nothing is really written in blood on this, but it does help for planning somewhat.. Good luck and have fun with it..

Robbie

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NG9R  



Joined: 11 Jul 2005
Posts: 5
Location: Camp Point, IL

PostPosted: Fri Jul 15, 2005 7:32 pm    Post subject: Reply with quote

Hi Robbie,
I am sure the coverage is much less than it should be right now due to a damaged antenna. The actual transmitter power is 80 watts, but the feedline loss negates quite a bit of this. I am getting ready to burn a new EPROM with newer UIdigi code and am looking through the options of what parameters to use.
Using 49 watts with the antenna gain of 6 at 320 feet calculates to a 49 mile range (not sure if that is radius or diameter), using 36 watts only reduces the circle to a bit over 45 miles, both quite a bit optomistic I beleive. Due to the damaged antenna and no stations on in the favored direction of the antenna, it is hard to say. I live on the bad side of the antenna pattern and although the digi is full scale here at home, I cannot reliably hit it with my home station, much less my mobile tracker.

Danny NG9R
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Robbie  



Joined: 02 Jul 2004
Posts: 32
Location: Buffalo Grove, IL

PostPosted: Fri Jul 15, 2005 8:09 pm    Post subject: calculating PHG Reply with quote

Hi Danny,

Doesn't sound too good there.. You don't say anything about the distance between you and the digipeater, but generally in my experience, if I hear something full quieting and I don't make it back to the digipeater when I am running 10 watts and don't make it reliably, I either have a problem with my antenna, or the digipeater is really dead on receiving, Smile Where some people make the mistake Danny, is a repeater or digipeater can be full scle full quieting and you don't make it back with a rubber duck antenna or 5 watts to a ground plane in the attic or on a file cabinet..

I know I am guessing, but that bites a lot of users, as I don't know what you are using at home, and are you also using something like 5 watts in the tracker.. Again, I am guessing, but you are finding more and more aprs users wondering why their talkies are not doing well, even in a "quiet" network, not like the northern side of Chicago..

The more 5 watt trackers, the more "home relays" are needed. If no home relays, you have to hit the digipeater and if it is more than 10 to 15 miles away, a 5 watt mobile fluttering along is doomed... A lot of issues to be solved Danny and alot of experimenting. First, it sure would be great to get that antenna problem solved for sure!

Robbie

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ka9vnv  
Site Admin


Joined: 08 Jun 2004
Posts: 152
Location: Woodstock, IL

PostPosted: Fri Jul 15, 2005 9:58 pm    Post subject: Reply with quote

PHG is a relative measurement, no matter what. The "gain" is supposed to be the net system, taking into account the antenna's dbd gain (while most publish dbi, which is 2.14db higher than dbd), minus the feed line losses.

The height gain seems to be the biggest factor in circle drawing... Although versions of WinAPRS through at least 2.6x treat "0 db" as "zero output", rather than "unity gain", so putting a zero in any field other than the directivity meant Win/MacAPRS users have no range circle for you.

Personally, I'm not an advocate of running big power on a digipeater, for the reasons Robbie aluded to... I want any station that can hear the digi to be able to work it, so if the sensitivity is down, the power should be, too. I'm violating that on VNV-15, because I needed to move the power up to reach adjacent digis from its current location... The old site worked wonderfully with 5 watts out.
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NG9R  



Joined: 11 Jul 2005
Posts: 5
Location: Camp Point, IL

PostPosted: Sat Jul 16, 2005 11:05 am    Post subject: Reply with quote

Robbie, you are correct about my tracker, it is 5 watts to a 5/8 wave on the roof of the truck. It actually performs much better than I expected, between my igate at home (16.5 miles from the digi) and work (3 miles the other side of the digi) I only lose a few posit packets, although the local traffic is almost non-existant. The home station is only 10 watts ERP at 15'. I hope to move the current digi to another site with a better antenna in the next couple of weeks. That should eliminate at least one problem.

Hello KA9VNV, thanks for the input and the site. I agree with all you say, but I have to work with what is available, at least until more of the club members show some interest in APRS and justify the club spending more money on it. The current hardware was on 145.01 for years and I convinced the club to allow me to convert it to APRS use, at my own expense. Right after I did, we found out the antenna was damaged and it really does affect the performance pretty drastically.
I guess the range calculations assume equal performance for receive and transmit, which is far easier to measure than receiver performance. I know this digi is quite an alligator, but I hope to remedy that soon.
Do you know if the range circle calculated is diameter or radius?
edit: I found the answer in the APRS notes, it is radius.

Danny NG9R
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