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Author Topic: Receiving Repeater Wierdness - Can't blame the oak tree  (Read 3832 times)
K5AJ
Member

Posts: 14




Ignore
« on: March 29, 2017, 09:12:47 AM »

Situation

Reference   This eham link.
where I incorrectly suspected a Yeasu 400 problem., and I apologize to Yaesu employees and users for, what amounts to, disrespect to Yaesu.

Situation:

My rig to distant Yaesu fusion repeater on 500 ft commercial tower.
30-40 miles between
Jan and Feb.  Yaesu 400 at 5 watts, Loud and Clear both send/receive
to other repeater users.  Wouxun HT to same antenna, Loud and Clear both directions.

3 separate VHF 23 ft high antennas, to experiment with, including 4 element Yagi
pointed thru 70 ft green oak tree toward the distant repeater.

Transceivers: Yaesu 400 or Wouxun 5 watt HT.
Transceiver tones - correctly set

Problem beginning this month:
Unable to receive any more than squelch noise and weak/untelligible transmissions from other repeater users.  They hear me Loud and Clear.

Hitting other repeaters scattered around the county, all good, both directions, usually Loud and Clear.

Attempts to isolate the receive problem.
Antenna Analyzer:"
Coax 1  SWR on repeaters freq. 1.4:1 or better
Coax 2, same as above
Ohm'd out both coax's all good.

Tried 3 different antennas, including the yagi.
My transmit to repeater, other users here me Loud Clear
Receive back: Weak and untelligble.
Yaesu 400 to each of 3 antennas, and over different coax - Same as above
Wouxun to each antenna and over different coax - Same as above

Tried same procedures after full reset on each transceiver,
then using VFO modes, same problem.

The Fusion repeater owner insists that his repeater is in perfect working order. 
Other repeater users contend same thing.  Fusion repeater defaults to FM non-digital.    For me to put up a 100' tower is not going to happen unless other hams want to buy it for me.

The only thing different; I could communicate both ways perfectly
in the winter, with no leaves on big oak trees.

Propagation experts tell me that, if the oak tree is interfering,
that my transmit should be equally as bad as my receive, and
that there should be an equilibrium of send/receive signals.
Repeater owner says same thing.  And so they say, I cannot blame the oak tree.

Unless you guys notice something I failed to try; my recourse is to
wait until winter, when the leaves fall off, and try again.  I think it's unlikely that 2 receivers would go bad on one same frequency. 

Thanks for indulging all this. Smiley
Jack
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W9IQ
Member

Posts: 1652




Ignore
« Reply #1 on: March 29, 2017, 09:59:35 AM »

Jack,

Reciprocity applies to the antennas involved. Differences in transmit power and receive sensitivity for example,"unbalance" the notion of reciprocity when applied to the entire system. But in any case, the repeater should be putting out 25-50 watts (assuming a barefoot DR-1). This is at least 5 times the power you are using to hit the repeater yet you cannot hear the repeater in summer conditions. So clearly something else is going on other than simple tree attenuation. It might be worth asking the repeater trustee what is their output power just to confirm this. I would also ask if they send and receive from the same antenna.

One possibility might be fringing or re-radiation. These are not always reciprocal effects when they occur as a result of building edges, water towers, etc. Part of the lack of reciprocity here can be explained by the difference in elevation and take off angles of the two antennas involved compared to the spacial position of the objects. So if you are receiving a signal that is a result of fringing, that signal could be sufficiently attenuated in summer by the trees while your transmit signal is making it there by another route.

Another possibility is coax problems. I know you said you did SWR and Ohm checks but your description has the classic characteristics of bad coax / bad coax connectors. Did you do distance to fault and attenuation measurements as well? Did you do a remote end open and a remote end short test when ohming it out? It seems unlikely that two coax cables would show the same problem, but I have seen stranger things.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
N5XO
Member

Posts: 145




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« Reply #2 on: March 29, 2017, 04:30:55 PM »

Good afternoon,

I am the repeater owner, so I can answer the questions regarding my station.

Elevation:   2043 ft
Tower:        140ft, antenna mounted 140ft
Antenna:     DB224 Omni Pattern
Feed:          1 5/8 hard line 150ft, LMR 600 final feed 8 ft
Repeater:    Yaesu Fusion @ 50 watts {using a 100 watt continuous duty PA, driven by the Fusion}

Amateur with the communication problem, aprox 712ft elevation, antenna aprox 40ft. Repeater RF path 35.4 miles.

I think the answer below regarding multi path may have some merit. Due to my schedule I have not been able to get over to his location and evaluate, however operating mobil less than a mile to mile and half from his location, the repeater is 3/4 to full scale. There are some obstructions in the path between him and the repeater, that can interfere with the signal and as you drive down the highway 3 miles plus and minus his exit, the signal can go from 1/4 scale to 3/4 scale in just that short distance and back again.

What is puzzling is that at 5 watts he is not full quieting into the repeater, but by 20 watts he is, yet he can not hear the repeater in any fashion.
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KB1GMX
Member

Posts: 1485




Ignore
« Reply #3 on: March 31, 2017, 12:04:16 PM »

Lets assume the fusion repeater has a set of cans for a diplexer....

WHAT DO YOU think the loss though those would be?Huh

Hint more than 3Db is common so the 50W repeater is putting maybe 25W to the antenna.
if there is no desens you can expect it to hear you better than you hear it.

I've worked many repeater here in the east mobile at greater distances with
the repeater at the same power.  But during summer I do need a bit mroe power for
the same quieting at the repeaters due to trees.

So the oak does count but maybe not as much, what isn't said is how many
other oaks pines and what not are there at that height between you and the
repeater.

The test is higher antenna or move it.  Maybe the coax as a bad connector and
moving it makes it work (or the connector it goes into).

The conflict is you say other radios have no issues then get rid of or fix the offending radio.

that and after reading two strings there are details that are unanswered.

Allison
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WB6BYU
Member

Posts: 16898




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« Reply #4 on: March 31, 2017, 07:39:05 PM »

Is the yagi the only one pointing through the oak tree?

Is the tree now fully (or mostly) leafed out?  Or are the leaves still sparse?



My guess would be a multipath problem, though those often change
when the antenna is moved a few feet.  If you see the same symptoms
With 3 different antennas mounted in different locations, that
makes it less likely, but still possible.

With multipath, the signal at the receiver depends on the relative
signal strengths and phase shifts over multiple paths.  Because RX
and TX are on different frequencies, the effects will be different.
I had one particular repeater where, at one traffic light, rolling the
car forward to peak the received signal strength put me in a null
for my TX path, and vice versa.  I had to stop with the meter
mid-scale to have a 2-way conversation.

There are other possible causes other than the tree - did anyone
put up a new building nearby?  I know of one knife-edge diffraction
path that stopped working then the hillside was logged, and we used
to joke that when the "doldrums" were particularly bad on my way
to work it was going to be a nice day - apparently the path acted
differently when there was dew on a hillside than when it was dry.

One obvious symptom of multipath is that the S-meter reading
is different with modulation than with an empty carrier - that's due
to the change in phase shift with frequency.  But I don't know
if you can see that on digital modes.


If it is multipath, try moving the antenna around and see if you can
find a location where it works better.
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N8EKT
Member

Posts: 582




Ignore
« Reply #5 on: April 01, 2017, 07:13:06 PM »

My guess is that you are in a null area for the repeater's antenna pattern which puts you in a marginal signal to start with and the leaves simply make it worse

Side mounting a VHF antenna on a commercial tower always yields a distorted pattern with deep nulls in some directions

We have a 2 meter repeater in my area that has a 50 watt repeater and an antenna mounted on the east side of a commercial tower at about 1500 ft elevation

I can't even hear the repeater from the highest point in town just 9 miles to the west at 1340ft elevation
















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AA4HA
Member

Posts: 2375




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« Reply #6 on: April 02, 2017, 09:06:02 PM »

You can also have a blown out first RF stage in your receiver or even intermodulation on frequency from mixing of other transmitters/oscillators.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
WB8VLC
Member

Posts: 412




Ignore
« Reply #7 on: April 02, 2017, 09:11:54 PM »

Since other repeaters are fine on your receive then another thing to consider is some local interference on the repeater frequency in your vicinity that's blocking your receiver.

I just had a similar issue today on 6 FM, 50.3 simplex,  where my tx was full quieting while on receive a local base station at just 3 miles out was in and out while the same base station on 50.5 and 51.0 MHZ was full quieting.

After considerable searching I found a spur from a Mr. Coffee Machine blocking the receive, some quick searching with a SIGNAL HOUND SPECTRUM ANALYZER lead me to the noise source.

This POS MR. COFFEE MACHINE is now a candidate for my rendition of the copy machine in the movie OFFICE SPACE.
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WG8Z
Member

Posts: 304




Ignore
« Reply #8 on: April 04, 2017, 07:27:24 PM »

local desense? cable tv leakage?  noisy wall wart?
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KOP
Member

Posts: 213




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« Reply #9 on: April 06, 2017, 11:20:59 AM »

Aliens?
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KC9V0
Member

Posts: 29




Ignore
« Reply #10 on: April 12, 2017, 08:43:18 PM »

You need to check the receiver sensitivity on the Yaesu FTM-400. It is most likely too high. Have you tried a simplex channel to see if you get the same symptom?

73
Chuck
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