Tearing my hair out

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Tearing my hair out

Postby M0TRJ » Thu 2 Jun 2016, 15:13

Been away from 4m for just over a year used to have perfect qso's.

cleaned the dipole and cx4-68 checked with analyser both 1.2:1 across the fm portion.

Friends said they heard me good and strong even 35 miles away but i cannot hear anyone over 10 miles from here.

I tried both antennas with different feeders 2 radios my trusty ascom and my new at 588

No different so am i being de-sensed ?

I went portable with 1/4 wave antenna and could hear my friends and they me again out to 35 miles

Have run sdr around 70mhz have tried freq counters have run base antenna to car so no mains used and no close plt's.

Its doing my head in something is blocking the incoming signals.

Any help to stop me becoming more bald or turning to drink and or drugs grate3fully accepted.

73

Simon
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Re: Tearing my hair out

Postby GW8IZR » Fri 3 Jun 2016, 06:00

from your description it sounds like the noise floor is elevated by local noise, this is limiting the ability of your receiver to detect signals below this elevated noise floor.

you mention that you have tested with an SDR but you haven't said what the results were? if you look in a narrow bandwidth at the frequency you are trying to use what is the noise floor? If you connect and disconnect the antenna does the noise floor increase?

Assuming your post code is the location where you are using the equipment I see you are almost at sea level and in an urban environment, street view shows a roof top antenna at chimney level which may be yours, I guess 25 or 30 feet. From that height and with todays noise levels I suspect your coverage wont be stellar anyway and if the noise level is high then the link budget will not be reciprocal.

HTH
73 de Paul GW8IZR
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Re: Tearing my hair out

Postby M0TRJ » Fri 3 Jun 2016, 10:13

Many thanks for that but what I don't understand is I never had this problem last year and why if I leave the immediate area in the car with 1/4 wave whip (no loading) I get out ok? I am at a total loss. i don't hear any noises or think the normal background noise has changed. Definitely the Ascom rig has been in same place and unaltered, squelch is set as was when i could hear out much further and yes the antenna is that high but that is not it.

I ran the sdr from 68 - 76 mhz in case of a local noise that could be affecting me nothing showing. The frequency counter shows signals around 42mhz and 28mhz. Its weird ? especially as ALL the people i talk to say 57- 59+ signal strength from me but i cannot hear them.

That said a guy 24 miles from me broke the squelch with a 57 signal but all i got was noise no audio.

Guess im selling the 4m gear

Noise floor on sdr showing 58.6dBFS Peak 56.6dBFS SNR 2.0db
Last edited by M0TRJ on Fri 3 Jun 2016, 10:44, edited 1 time in total.
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Re: Tearing my hair out

Postby GW8IZR » Fri 3 Jun 2016, 10:34

Well I think you have kinda answered your own question there ;-)

If you drive away from your site the receiver is fine - so something local to your site is increasing the noise floor.

Why wasnt it there last year? - well maybe someone nearby has bought a new PC, laptop, mobile phone charger, dsl router etc.. maybe one of those is increasing the noise.

4m is quite prone to high levels of noise when you are located close to other electronic devices, here in an urban location in Bolton the noise on my horizontal dipole is S9 on the scanner. Looking with an Airspy at a wide bandwidth the noise isn't really significant but if I narrow the bandwidth I can clearly see the troublesome noise.

The same RX setup at my home in Wales the noise level is nil.

You can either give up and only operate away from home *or* investigate further. It must be a fairly big signal and as its most likely wideband you will need to develop some skills DF'ing it. you need to try an AM receiver, I use a really cheap Yupiteru hand held scanner with a dipole and get out there and look for it.
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Re: Tearing my hair out

Postby M0TRJ » Fri 3 Jun 2016, 10:49

Yes i have a scanner Yupiteru guess thats it Many thanks Paul

73

Simon
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Re: Tearing my hair out

Postby GI0GDP » Fri 3 Jun 2016, 12:18

HI Simon,
Just re read all of this and i am wondering does this problem occur after dark?
This would remove PV installations from the equation.
regards
Geoff
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Re: Tearing my hair out

Postby M0TRJ » Fri 3 Jun 2016, 18:21

Its 24/7 Geoff

There are some spikes of activity across the bands as i narrowed the filter on sdr receiver they became apparent not sure what they are or where from i am in process of making hand held dipole for df

Simon
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Re: Tearing my hair out

Postby M0GJL » Mon 13 Jun 2016, 15:42

I've used this spec-an with a SDR dongle.. works quite well... https://github.com/pavels/spektrum
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Re: Tearing my hair out

Postby M0TRJ » Mon 13 Jun 2016, 16:39

Thanks setting up now
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Re: Tearing my hair out

Postby M0TRJ » Mon 4 Jul 2016, 00:55

One more question do you think that an lfa yagi from innovantennas vertically polarised help eliminate the noise
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Re: Tearing my hair out

Postby GW8IZR » Mon 4 Jul 2016, 06:28

I think you need to trace the source of the noise first, then work out a mitigation strategy.

Whilst a directional antenna *might* help, if the noise is in the direction you want to receive it could make things worse.

Height may help to get your current vertical antenna above the noise but we wont know till we at least know what the source is.

Regards Paul

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73 de Paul GW8IZR
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Re: Tearing my hair out

Postby MØXTA » Sun 10 Jul 2016, 08:03

Even if you have a noise issue on 4m. please don't give up the band....

We need more people across the UK and beyond on the 4m band than ever before. You can just try and simply track down where this noise is coming from....

it could be the TV? dirty power supplies? Solar panels? These things within your own home or from your neighbours?

If you don't have a 4m rig that doesn't have a signal meter, then you will never know if you are suffering with noise or not. I own the Anytone AT588. It's a lovely rig that does 50W of power and has a reliable signal meter.
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Re: Tearing my hair out

Postby M0TRJ » Sun 10 Jul 2016, 10:52

I am having difficulty finding a single source of interference. M0GJL told me about an excellent spectrum analyzer which is showing lots of small spikes across all of 70mhz. I have the excellent AT588 but it does not show any signal strength leading me to believe that the noise is not in immediate vicinity. I have a yupiteru 7100 scanner with a 70mhz rubber duck antenna and cannot hear anything breaking the squelch.

Any suggestions on what i might be doing wrong would help.

Also with the AT588 if i leave the bandwidth at 25khz i hear no stations but when its at 12.5khz i can hear the local stations.
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Re: Tearing my hair out

Postby GW8IZR » Thu 14 Jul 2016, 07:54

a strong off frequency carrier can close a traditional NBFM squelch circuit.

Have you disabled the squelch, can you then hear signals.

Have you tried a different channel to assess the symptoms?

Regards Paul
73 de Paul GW8IZR
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Re: Tearing my hair out

Postby M0TRJ » Thu 14 Jul 2016, 11:16

Hi Paul

Yes i have tried squelch off and 12.5 20 and 25k widths, no discernable difference.

I will have to just walk around immediate neighbourhood to see if anything opens the squelch on my scanner then try the frequency counter with the 70 mhz rubber duck.

I don't want to give up on 4 meters as there's quite a few people using it.

Thanks for everyones input

73

Simon
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