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Offline 9a4qv

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« Odgovori #15 : 10. Lipanj. 2021, 08:42:43 »
Pozdrav,

ako je smetnja in-band onda takav pasivni filter neće pomoći u otklanjanju smetnje.
Smetnju koju proizvodi radar na Učki je in-band smetnja. To se manifestira na način da je signal prljav i širok i pokriva cca 200 kHz. Nažalost i 1296 MHz je unutar tih 200 kHz.

Ja imam sličan filter o kojem govorite i on neće riješiti problem radara. Dinko, takav filter možeš i sam napraviti, S53MV ima dobar članaka na tu temu a ima i SW alata za proračun filtra.

Smetnju koju ima Gogo ne znam kako se generira, da li je problem saturacija 23cm RX-a pa onda on generira takve probleme ili intermodulacija na objektu što je malo čudno na tako visokoj frekvenciji. Ne znam kako izgleda tvoj setup, ali smrdi mi na pretpojačalo ako postoji u tvom sistemu. Samo ga zaobiđi kada si na takvim čukama i sve će raditi OK i sa golim transverterom.

U svakom slučaju, da bi vidio da li je smetnja in-band ili generirana u RX-u potreban je spektralac na lokaciji da se to ustanovi.

QV
"I do not think that the wireless waves I have discovered will have any practical application."
Heinrich Rudolf Hertz

Offline 9a6c

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« Odgovori #16 : 10. Lipanj. 2021, 09:16:17 »
Adam,

To je onaj transverteri koji je bio kod tebe na kanalu, znači DB6NT tvtr, lna i mali qro pa iza njega dg0ve na kojem piše 20w, a ti izmjerilo 50 ;D

Na lokaciji u jn73ws sve bilo ok, a u jn83cw šum konstantno 20 dB iznad devetke.

Čini mi se da je Bert spominjao i notch koji bi svakako pomogao oko neke i band smetnje, a sam filter na 23 cm svakako ne. Ipak mu je passband u MHz.

Za sad čekam i prijavit ću utiske😉

GG

Offline 9a6ar

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« Odgovori #17 : 10. Lipanj. 2021, 12:12:29 »
Adame hvala za tip, vidio sam filtere od Matijaza.
Super ideja za gradnju.
73 6ar
Nikad nije tako loše da ne može biti i gore !

Offline 9a4qv

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« Odgovori #18 : 10. Lipanj. 2021, 13:31:42 »
Gogo,
tebi će samo brikanje LNA riješiti problem na takvim lokacijama.
Također BPF ti može pomoći plus dodatni notch na tom filteru ako znaš koji ti je najjači ometač na lokaciji.
Da pojednostaviš, makni LNA iz RX grane.

Dinko, tebi nema pomoći :-)
Snimim ti danas sa maxhold kako izgleda taj signal sa Učke.
Stara je to priča koju smo žvakali još dok smo imali ATV repeater na Učki i kad je došao radar nije bilo pomoći.
U Zagrebu su se riješili problem tako da su promijenili kanal na radaru, čini mi se po privatnom zahtjevu bivšeg predsjednika saveza. U Zagrebu je svanulo na 23cm ali se nama u Istri i sjevernom jadranu smrklo....tako to ide..
 ;D 8)

QV
"I do not think that the wireless waves I have discovered will have any practical application."
Heinrich Rudolf Hertz

Offline 9a6c

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« Odgovori #19 : 10. Lipanj. 2021, 14:50:06 »
E, lako je tebi govorit, makni lna... Ionako san star i gluv, makni mi slušni aparat i di san onda?

Radije iden na brdo iznad kuće pa pomalo.

I ko će krivit one kabliće i sma konektore?

Srediću ja to nekako.

Za AA sve je spakirano😉

Offline 9a4qv

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« Odgovori #20 : 10. Lipanj. 2021, 15:09:54 »
I bolje ti je na brdu pored kuće nego gore na Promini...
AA CU...
"I do not think that the wireless waves I have discovered will have any practical application."
Heinrich Rudolf Hertz

Offline 9a6c

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« Odgovori #21 : 10. Lipanj. 2021, 15:29:10 »
E kad mi vrag ne da mira...

Vidićemo kako će bit u AA... Povrh kuće su crkva i groblje i normalno da nema šuma😋

Grobna tišina na 151 m asl...

GG

Offline 9a6c

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« Odgovori #22 : 11. Lipanj. 2021, 15:04:19 »
Momci, javio se Matej Ok1TEH koji prati ovu našu raspravu oko mikrovalova i poslao malo duži mail s molbom da ga ovdje objavim, a mislim da ga vrijedi pročitati. Na engleskom je, ali uz malu pomoć Dr Googla mislim da će biti zanimljivo ;)

***********************************************************************************


Hi guys,
I'd like to write out few findings related to problem with 23cm QRM
from commercial or military towers and how to remove it. First you
must find out if the signal is in band or not by some spectral analyzer.



1) QRM by inband commercial signal
If the signal make problem in band, there is usually very little
what you can do.. One partial solution is to build up narrow dish
with high front to back suppression and use LNA with high IP3..



2) QRM by outband signal
If the QRM is caused by signal out of band, it's very important to
find out, how far (MHz) is the unwanted signal. At my home QTH in Prague
I had problem by DVBT2 tower operational some 300m far with few kW.
It was running DVBT some 300MHz below 1296 MHz so in this
case it was relatively easy to buy or make low ATT filter.


Making such a filter is relatively easy, we made such a filter
to suppress the mirror for the 28/1296 MHz transverter check out:
http://www.ok2kkw.com/00000104/preselector/bpf_23cm.htm
I asked to Beert, PE1RKI, because he has very well done boxes and machinery
and at least it saved lot of time. In the case it was easy because the
source of QRM was several hundreds MHz away so the
cross attenuation was only of 0,2dB.



Much worse situation happed at our contest QTH JO60JJ,
as we suffer from radar from from 14,4km far Auersberg radar
which is operating around 1259 MHz with 2,5 MW in pulse.
As the result I asked to RKI to prepare special narrow BPF version
however due to very narrow bandwidth and very high suppression
it has relatively higher cross attenuation. It's because of problem
with Q at this high frequency. Luckily we found out that such a filter
at our case was working well even when it was placed between
LNA and transverter, so the higher attenuation was still acceptable
because the whole noise figure wasn't  corrupted so much
(we use separated RX/TX path).



By the way if you have such a problem at 2m with FM BC,

check out https://www.antennas-amplifiers.com/144mhz-bandpass-filter-bpf

it's great BPF and I use it with good success..



3) QRM by usage of bad kind of LNA for contesting
For city environment with strong outband signal it's better to use
LNAs with very high IP3 like MMIC PGA103+ or some alternative.
Don't use 2 stage LNAs like VLNA from G4DDK or old LNA
with MGF1302, they are fine for EME, but not for city environment.

I had bad experience with LNAs from SSB electronics, little bit better
are HEMTs (Kuhne), better is PGA103+ but currently the best is probably LNA
from US4ICI with SKY67151, compared to PGA103 it has much lower NF
https://vhfdesign.com/lnas/lna-eme-sky67151-for-23cm-and-21cm-bands.html
Remember for 23cm tropo contests that you really don't have to use 0,1dB NF LNA,
anything below cca 0,8dB is ok (because of high thermal noise from background)



4) Operation at on4kst chat
I read your discussion, It's not easy task.



At 23cm I used to ask to more people, because I use 2 or 3 (since June)

independent antennas, so I can turn them to more stations at the same time.

Sometime it's problematic that you ask somebody for chat and you are called

at random by some other local station, so sked partner has to wait and with

nowaday smaller patience he became to be angry, that he must wait for you...



I always try to do my best and ask stations only if I checked at Airscout
that airplane is already coming. But guys please release that the situation
in Middle Europe is far different to some DX area like 9A. We oftenly work
30 stations on 23cm during first 1 hour of contest so the pileup is big
however when you wait and ask some 9A station later like around 19utc
when you have more time for skeds, at the meantime he often go QRT
or try some other band.. An another thing is QRM situation, I often ask
the sked partner to move let's say to  .310 or higher.
During some contests it's very problematic to find any free frequency
for CQ between 1296.150 to 1296.290 MHz...



In any case if you are fed-up with the too fast chat traffic, try use our VUSC

contest log because it has it's own KST chat client with very good

user text filters. If you are QRV 23cm, please write it at your name in

chat and if you are just listening, please select in KST chat that you are

"off the chat" so then is station marked with () and almost nobody will bother you.



At the end I must say that S5, 9A and YU operators are very well skilled
in CW/SSB operation so it's big pleasure to work you. And yes of course

please always send full rst+nr + loc code, the situation when
somebody send rst+nr only I don't like either hi. Last words: if you are small

stations with 10W, please realize that Airplanes are great help so even with

your small setup if you know CW, it has sense to try QSO up to 500 km,

just give it a try and please be patience hi.



73
Matej, OK1TEH

********************

Najbolje od svega mi je što je teško naći slobodnu frekvenciju  i da postoji pile up na 23 cm, e da mi je to doživit...

Naprid naši!

73 GG

Offline 9a4qv

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« Odgovori #23 : 12. Lipanj. 2021, 19:46:41 »
Hello Matej,

just for the curiosity, I left the SA on max hold for a 15 min to plot the spectrum.
What you can see is the spectrum of the FPS-117 Long range radar system capable of plotting the targets at 470km!
L-band or NATO standard D-band 1215-1400 MHz (18 channels).
Av.power is 4.5kW max power 24.6kW with the 44 active Rows (antenna with amplifier).

This plot was created with a 10el.cheap yagi indoor using the 4mtrs RG-223 coaxial cable and HP8559A SA to be on the safe side.
The NF of the SA is really high, no external preamp used. Radar distance cca 30km.
Center frequency 1296MHz, span 200MHz, ref level -10dBm.

So, who is that fancy guy that can solve this problem using a passive fiter technics? Just show us that guy  ;D

In band signal from the radar is -50dBm at 1296 MHz....
"I do not think that the wireless waves I have discovered will have any practical application."
Heinrich Rudolf Hertz

Offline AD6IW

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« Odgovori #24 : 13. Lipanj. 2021, 06:32:19 »
There is relative easy way to cancel radar or other sources of interference, without using any filter.
Using phase canceling method, separate antenna pick up interfering signal, and combine that signal after amplitude and phase adjustments in main receiver.
Signals with same amplitude but opposite phase will cancel each other.
In reality it would be possible to reject interference up to 40 - 45dB. Another advantage of this approach is that interference or jamming signal could be at same frequency of weak signal.
 73 Goran AD6IW
« Zadnja izmjena: 13. Lipanj. 2021, 07:29:32 AD6IW »

Offline 9A2M

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« Odgovori #25 : 13. Lipanj. 2021, 13:41:03 »
To dečki, drago mi je da se ovaj forum vraća opet u život. Tehnika, propagacije... a ne svađanja i trolanja.
AD6IW posebno mi je drago da si i ti opet ovdje aktivan.
73 de 9A2M, Hrvoje

Offline 9a6c

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« Odgovori #26 : 13. Lipanj. 2021, 17:12:39 »
Malo smo off topic, ali rekao bih da je problem sve vremenski pa možda i nismo😔

Offline s55m

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« Odgovori #27 : 15. Lipanj. 2021, 13:39:44 »
To sa brisanjem radara sa signalom u protufazi je tocno, ali ako radar vrti antenu, tesko ce ga biti uloviti po amplitudi i fazi...

Offline s55m

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« Odgovori #28 : 15. Lipanj. 2021, 13:57:43 »
Hello Matej,

just for the curiosity, I left the SA on max hold for a 15 min to plot the spectrum.
What you can see is the spectrum of the FPS-117 Long range radar system capable of plotting the targets at 470km!
L-band or NATO standard D-band 1215-1400 MHz (18 channels).
Av.power is 4.5kW max power 24.6kW with the 44 active Rows (antenna with amplifier).

This plot was created with a 10el.cheap yagi indoor using the 4mtrs RG-223 coaxial cable and HP8559A SA to be on the safe side.
The NF of the SA is really high, no external preamp used. Radar distance cca 30km.
Center frequency 1296MHz, span 200MHz, ref level -10dBm.

So, who is that fancy guy that can solve this problem using a passive fiter technics? Just show us that guy  ;D

In band signal from the radar is -50dBm at 1296 MHz....

I fight with 180cm dish and discard any attempt of qso over the radar path. Had a lot of burned front-ends (23cm 13cm 9cm 6cm) on JN76PB because of weather radar on Lisca. But is it truth, that it was 50m away :). Even so close (radar is working on 5.61GHz), i was able to use 6cm band without problems.

Offline AD6IW

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« Odgovori #29 : 15. Lipanj. 2021, 16:20:12 »
Citat:
To sa brisanjem radara sa signalom u protufazi je tocno, ali ako radar vrti antenu, tesko ce ga biti uloviti po amplitudi i fazi...
Main lobe of radar will be rejected up 40-45dB, sto je bitno. Za potpuno ponistavanje signala treba signal processing.
Citat:
Had a lot of burned front-ends (23cm 13cm 9cm 6cm) on JN76PB because of weather radar on Lisca.
Stavi limiter ispred LNA
« Zadnja izmjena: 15. Lipanj. 2021, 18:32:56 AD6IW »