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Author Topic: They can hear me, but I can't hear them!  (Read 4719 times)
HS0ZIB
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Posts: 653




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« on: September 11, 2010, 10:08:32 PM »

I operate from Thailand, primary on 20 meters PSK31 with 100 watts from my TS-850S into a vertical antenna (Zero-Five 43 foot).

I can work stations in Japan, Asiatic Russia etc all fine.

When I check who spotted me, I see that my signal is reaching far and wide, with regular reports from Europe and the USA.

But I never see a trace of signals from these continents on my waterfall!

Clearly, my signal is getting out OK, but I'm just not 'hearing' signals from these locations.

I've checked my station cabling and it all looks OK, especially since I can hear and work stations up to a few thousand kms away.

Is a vertical antenna bad for reception?  I always though that the law of reciprocity would apply for transmit and receive. If they can hear me, then I should be able to hear them, (generalisation).

Simon
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STAYVERTICAL
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Posts: 875




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« Reply #1 on: September 11, 2010, 10:45:37 PM »

Hi Simon,

I use a vertical and have a similar problem.
My noise level is pretty high and I have the preamplifier switched off most of the time.
However, the stations in europe etc may not have good transmitting antennas and may be power limited as well, so they can't get through to you.
I have found my vertical is a real DX magnet, but tend to hear the same stations on psk31 night after night.
On rare occasions, when the solar flux is up the DX really pours in, but most times it is just gray line stuff.
One thing I have noticed is that stations within 500 miles of me are very weak, as verticals do not receive high angle radiation very well.
But for low angle stuff they really shine.
Being low angle, a small shift in the ionosphere layer height will move your skip zone a great deal, so verticals tend to be prone to a lot more qsb in my experience.
I frequently get severe qsb in these poor propagation times, to the extent that the whole PSK31 20m (14.070) band goes and comes in waves like the seashore.
The screen goes from full of signals to blank and back again.
If I time the wave well, I can get in and out before the wave collapses.
Who said ham radio was not a sport? hi.

I would not worry about your antenna Simon, its just conditions, and the way verticals work.

Hope to work you one day.

73s
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N4CR
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Posts: 1757




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« Reply #2 on: September 11, 2010, 11:30:13 PM »

If their noise level is much lower than your noise level they may very well be able to hear you but you can't hear them. Happens all the time.

The best thing I have done for my PSK monitoring station is to move the vertical WAY out to the back of my property and get it away from all of the noise up here by the house. It's made a huge difference in how well my Cushcraft R-8 vertical receives weak signals.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
K3AN
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Posts: 787




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« Reply #3 on: September 12, 2010, 10:22:47 AM »

Simon, its a generally-accepted fact that having a rare DX callsign adds at least 12 dB to your signal and even more if you're really rare.  Wink
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WB2WIK
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« Reply #4 on: September 12, 2010, 02:13:40 PM »

Simon, what's your noise level on 20 meters?

My first guess is that your noise level is higher than some others who are reporting hearing you.

And yes, I have found for some unknown reason that people not only exaggerate reports on the air (common) but also when spotting stations on the DX Cluster!  "Very strong" might really mean that the station thought he heard you, maybe. Cheesy
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N4UM
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« Reply #5 on: September 12, 2010, 03:55:45 PM »

Simon:

I note that you said you were running 100 watts on psk31.  This is probably between 3 and 5 times as much power as the typical psk31 station usually runs.  That may also help to explain why they hear you but you don't hear them.

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HS0ZIB
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« Reply #6 on: September 12, 2010, 05:40:43 PM »

Simon, its a generally-accepted fact that having a rare DX callsign adds at least 12 dB to your signal and even more if you're really rare.  Wink

Hi-Hi, that's true!  I have just returned from a 6-week investment visit to Laos.  Plenty of business opportunities but the cold, wet weather was no good for my bronchitus.  So no XW operation is forseen. Now there is a good possibility that I will have a job in Cambodia in a few weeks!

Simon
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W8JI
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« Reply #7 on: September 12, 2010, 07:06:20 PM »

I operate from Thailand, primary on 20 meters PSK31 with 100 watts from my TS-850S into a vertical antenna (Zero-Five 43 foot).

I can work stations in Japan, Asiatic Russia etc all fine.

When I check who spotted me, I see that my signal is reaching far and wide, with regular reports from Europe and the USA.

Simon,

PSK is a mode for people who want to be weak. It is unacceptable to run reasonable power, even 100 watts makes you running too much power.  So you are transmitting with more power, and perhaps a better antenna, than many stations calling you. You also might have high local noise floor.

If you worked CW or SSB many stations would run several hundred watts and have much better transmitting antennas. They would be much stronger than the PSK signals where most people run 20 watts or so to very modest antennas.



Antennas are NOT reciprocal for receiving ability and transmitting ability. On receiving, efficiency does not matter much so gain does not matter. Only the pattern matters, and how the pattern rejects noise and focuses on the good signals.

On transmitting, only the gain in the desired direction and angle matters.

I hope you see there are two distinctly different goals for receiving and transmitting!! A good transmitting antenna is not necessarily a good receiving antenna, and a good receiving antenna is not always a good transmitting antenna.





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N3OX
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« Reply #8 on: September 12, 2010, 07:08:37 PM »

Quote from: W8JI
PSK is a mode for people who want to be weak

 Grin
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
HS0ZIB
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Posts: 653




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« Reply #9 on: September 12, 2010, 09:28:34 PM »

Actually I should clarify my transmit power, since I didn't explain clearly in my OP.  My rig is capable of 100 watts (TS-850S), but the typical output power that I'm running for PSK31 is about 25 watts, since that is about the power level when I'm not over-driving the rig in this mode, (which would not be a good thing!).

Simon
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STAYVERTICAL
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« Reply #10 on: September 12, 2010, 11:43:58 PM »

Troll alert!
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G8UBJ
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« Reply #11 on: September 12, 2010, 11:52:21 PM »

I know it seems like a great idea to copy lots of signals in a waterfall but can you reduce the bandwidth of your receiver? This will improve the signal to noise and if you can get the filter nice and narrow you will suffer less  de-sense from adjacent signals which will hopefully allow you to copy those DX stations.

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N4KZ
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« Reply #12 on: September 13, 2010, 11:04:50 AM »

I've operated PSK31 on 20 meters off and on for several years. In the beginning, like many PSK31 ops, I liked operating with a fairly wide filter in order to see the whole waterfall of signals all at once. It was convenient and visually interesting. But in time I learned that it also limited me to hearing and getting good print on only signals there were moderately strong or stronger. The weak ones just didn't show up on the waterfall and I didn't even know they were there. Then I bought an Icom Pro 3 which has a 50 Hz digital filter just for this situation. Suddenly, seeing the whole waterfall at once is out but using the 50 Hz filter dramatically improved the signal-to-noise ratio. And meant suddenly I was seeing, hearing and copying weak PSK 31 signals like never before.

I came to the conclusion that I never realized there were so many European hams operating PSK31 while running 10 watts into indoor dipole antennas.

Operating with the 50 Hz filter can be tricky. With such narrow bandwidth, you essentially just see one signal at a time in the waterfall which means that VERY careful tuning is required. Or you can write rig control macros for the Pro 3 and automate the tuning process. I used MixW at the time and it worked very slick. I could manually tune in a signal using a wide filter, click on the waterfall trace and then click on my narrow macro. It caused the rig to tune the signal to the middle of the filter passband automatically and super weak signals then just popped up out of the noise like nobody's business. And it dramatically improved my ability to get excellent copy on signals that were extremely weak.

Using narrow filtering is the secret to weak signal PSK31 reception.

73, N4KZ
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STAYVERTICAL
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« Reply #13 on: September 13, 2010, 01:45:50 PM »

I totally agree with G8UBJ and N4KZ - I only have a 500Hz filter, but this makes a huge difference to reception, even enabling me to use the preamplifier.
The signal to noise ratio improvement alone is worth the price of the filter.
If you use computer control of the rig, such as CAT or the Icom equivalent, then Ham Radio Deluxe has a function called centering, which if you press the button, will adjust the rigs frequency so that the cursor signal is centred in the desired filter passband.
Multipsk also has a similar function, so using these programs make it simple to rapidly switch to a narrow filter.
I use the wide passband filter with the HRD/DM780 "superbrowser" to get an overview of the incoming stations, but the narrow filter when working.
The positive aspect of the poor conditions presently, is that we are all inspired to improve our stations and antennae to the greatest extent possible.
And isn't that what ham radio is all about?
Thanks for initiating this discussion Simon.

73s

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G0GQK
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Posts: 634




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« Reply #14 on: September 13, 2010, 03:00:07 PM »

I use a vertical antenna's for all bands and it is an unfortunate fact for me that I can see stations in Europe using yagi antenn'a at 30-40 ft in contact with Japan, but the JA stations never appear or are heard on my monitor. I've known occasions when I see the trace but the signal is too weak for me to decode and my background noise is nil. I often wonder why the only stations which most European stations are able to contact are mostly Japan and Australia, but today I saw a Philippines call and he was having contacts in mainland Europe but the trace was flakey for me.

I have a quarter wave vertical for 30/40 metres and on most occasions US stations see my 25 watt signal better on their screens than I see them. Some I know are using dipoles but on most occasions I am able to read a poor signal. There have been occasions when PY and LU stations have been almost invisible on the screen and yet I've copied every word.

I believe the reason for this is the quality of the transmission. When I operated 100 watt phone I always used a Heil HC4 microphone which is very "thin" and it penetrates the band noise, and I think the same with digital signals. A good 25-30 watt transmission will be seen much better six thousand miles away than a fat, oversized, distorted PSK signal which ia all "hairy". Examples of overdriven overprocessed SSB transmissions can be heard in every DX contest, they're rough, with no clarity.

However, I can assure you that if your signal is being heard in Europe there will be hundreds of stations calling you, but an SFI of 76 with dreadful QSB is not helpful for anyone in making DX contacts.

Mel G0GQK
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