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Author Topic: Should it be this hard to hit a digipeater?  (Read 16331 times)
N8FU
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Posts: 10




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« on: June 17, 2014, 02:42:19 PM »

I recently bought a TM-D710GA and tested it out in the shack.

I had it connected to a 2/440 dual band MFJ mag mount that was stuck to the metal strip on the top ridge of my roof. This is a tiny little antenna, 1/4 over 1/4 wave on 440 and 1/8 wave on 2 meters if I had to guess. Antenna height is approx. 25 foot above the ground, and I live in the second highest area in my county.
I could hear the packet audio from a digipeater 15.5 miles away, it was very clear sounding and would trip the squelch even when set almost full.  The radio only decoded 1 aprs packet in 24 hours.

After that I put it in my 4runner and became N8FU-9 with a temporary setup using an NMO mag mount and my new Larsen 2/70 antenna. I drove all around Columbus, OH with the radio on 50 watts and was never picked up by a single digipeater. Nothing showed up on APRS.fi. When on top of a parking garage at CMH airport, the NMO 150 did get one packet successfully sent, and I recieved a few as well.

The Larsen 2/70 has the same performance on top of my house. Never heard by the digipeater 15.5 miles away with 50 watts output.  However, when I switched the 2/70 out with the Larsen NMO-150b the radio decoded every packet I heard. The results are similar when mobile, with the nmo-150 the radio recognized maybe 1 out of 50-100 packets that I can hear. And occasionally the digi will hear my packets when I am on a hilltop. The nmo-2/70 gets nothing.

I have always heard such good things about the nmo-2/70 antenna and look forward to being able to use both bands on my new radio, especially for cross band repeat. With these results I am wondering if I have a faulty 2/70 antenna, or if it is just that much poorer of a performer on 2 meters. (I haven't had a way to do much 440 testing with it yet.) If it's just that poor of an antenna, I will have to look into 2 mono band antennas and a diplexer for my permanent setup.

To add to my frustration, there are many many comments out there saying things like:

"My problem was that with 5 watts, even with a 5/8 wave ground plane, I could not get the digipeter that was only 15 miles from me, and that was the closest... Same antenna with 10-15 watts and I was golden..."

or

"Unless you're out in the wilds of Northern Montana, you should be just fine with 5 watts and a decent antenna. When I lived in an area without local digipeaters I used a 1/2 wave antenna on the back of my bicycle and it worked just great... Even on I-70 in southern Utah ("next service area 150 miles") I get into digipeaters on 10 watts (TM-d700 on L power setting)."

I got so frustrated that I drove toward the digipeater that has been hearing me on occasion, and while sitting in the parking lot on the tallest hill I could find, (6 miles from the digi) the 2/70 still did not make it onto aprs.fi. And only 1 in 30-40 packets that I could hear were decoded on my radio as APRS. Switching to the nmo-150 had 100% success in packets received and sent.

I drove home with the nmo-150 on, and at 10 watts I was able to be tracked about half way back home before my signal disapeared.

Is this normal? For APRS in general or for the comparison between the 2 Larsen antennas?
Neither one seems to be even close to what I have heard of.

Thanks for any help you can give.

Carl
N8FU
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KD0SFY
Member

Posts: 289




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« Reply #1 on: June 18, 2014, 03:06:54 PM »

What did you have your digi-path set to?  I don't have the 710 manual in front of me, but usually you can set it to something along the lines of Direct, WIDE1-1, or WIDE2-1.  Generally for populated areas, WIDE1-1 is sufficient. 
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KD0SFY
Member

Posts: 289




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« Reply #2 on: June 18, 2014, 03:11:49 PM »

Just called up your track as N8FU-9 and it looks like you are set to WIDE2-1, so that is not the issue.  I run a Yaesu VX-8GR to a Diamond MR77 and have very little problem. 
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N8FU
Member

Posts: 10




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« Reply #3 on: June 19, 2014, 10:05:57 AM »

Yea, the path is not the issue, since the digipeater that I can hit occasionally is very close to an i-gate. So if the digi hears me, it makes it to the internet immediately.
It just seems to me that if it takes this much to hit a digi, then there are going to be holes all over the country where 50 watts won't even come close to being repeated.
And everything I read makes it sound like you can throw a tinytracker hooked to an HT and have a servicable APRS settup. Or at least something with 10-20 watts.

I can hear the packets quite clearly yet the radio rarely accepts them.

Carl
N8FU
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KD0SFY
Member

Posts: 289




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« Reply #4 on: June 19, 2014, 12:29:08 PM »

As far as the digis hearing you, maybe a frequency and deviation check is in order.  Frequency might also explain why you aren't decoding a lot of packets.  I do know that not every packet I can hear in my area is actually decoded.  Also check and see if you are running compressed or not.  Some stations can't handle compressed.  Also some stations are not running the WIDE1/WIDE2 protocol, they are still running the older protocol. 
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N8FU
Member

Posts: 10




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« Reply #5 on: June 23, 2014, 07:34:34 PM »

As far as the digis hearing you, maybe a frequency and deviation check is in order.  Frequency might also explain why you aren't decoding a lot of packets.  I do know that not every packet I can hear in my area is actually decoded.  Also check and see if you are running compressed or not.  Some stations can't handle compressed.  Also some stations are not running the WIDE1/WIDE2 protocol, they are still running the older protocol. 

These same digis work just fine with other antennas, or when I am closer to them. So the settings are working just fine. It just didn't seem right to be able to hear the packets so well and not have them decoded.

The biggest surprise was how much difference I found between the two Larsen antennas.
The NMO-150B was WAY better than the NMO-2/70 on 2 meters. After reading so many glowing reviews of the 2/70  I wasn't expecting such a drastic drop in 2 meter performance. I assume that the 2/70 is better than the NMO-UHF on 440. So I'll probably just use the 2/70 as a mono bander on 440.

Carl
N8FU
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KB4QAA
Member

Posts: 2369




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« Reply #6 on: June 24, 2014, 09:09:22 PM »

Expecting to be able to hit a repeater 15 miles away with 5 watts reliably, is  'optimistic'.  You may be able to do it, but there are lots of variables, and I would not consider it to be a given, or typical.

A quarter wave antenna has fairly high angle lobes.  This can be helpful in cities with repeaters on high buildings.  For longer distance contacts a 5/8wl antenna with it's lower angles can be better.

Take a look at your packet settings.  Back in the ancient days of plain packet, I and buddies spend many late nights over weeks tweeking things like paclen, tx/rx delay, etc to get first: any connection, then the most reliable connections and fastest speeds.  Minor changes can make all the difference.  Compare notes with other users, especially those with the exact same TNC, Radio and Software.

p.s.  I always carry both a 1/4 and 5/8wl antenna in the trunk and swap them out as needed for the situation.  1/4 for in town or 'low visibility' and 5/8 for road trips, search and rescue, and countryside operating.
« Last Edit: June 24, 2014, 09:30:07 PM by KB4QAA » Logged
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