I have removed the attenuator
First QO 100 test tx
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Hi Phil,
I am using a homemade helix and 13 W in a 60 cm dish and can activate Leila.
Detlev
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Hi,
I asked Hristiyan (SG Labs) about the mismatch. Here is the answer:
The amplifier is tested at VSWR >20 , 20W output power at all phase angles and it survives without damage and degradation.
Of course, it is not recommended to use it in this mode.
73 Hristiyan LZ5HP
Detlev
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Quote
The amplifier is tested at VSWR >20 , 20W output power at all phase angles and it survives without damage and degradation.
Which only states, that the will keep it's performance without getting worse. But that does not mean, that you will have actually 20W at a mismatched load. As an example: if you have an open coax cable end without any feed, the load is ca. infinite (expect for some minor reactive parts). I am pretty sure the power in this 'load' will be close to zero. If you then attach 50 Ohms again, the PA will deliver 20W again, as it was neither damaged nor degraded.
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Hi Achim,
Phil has 10 W at the end of the antenna cable, a VSWR 2.7:1 and an 80 cm dish. That should be sufficient. Meanwhile he removed his 10 dB attenuator, so his power must have increased.
Detlev
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I am glad you are confident it's fixed now, well done. I did wonder about rain drops de-tuning a POTY. They say the 3mm spacing between the plates is critical, so I can only imagine 10 or more raindrops between the plates must alter its resonant frequency and change the SWR. I wonder if a helix TX antenna suffers with raindrop de-tuning to the same extent, if indeed the POTY is significantly affected in this way?
What are you using to measure the SWR of the TX antenna? I have no obvious means of doing this at all with the equipment to hand...
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Hi Chris,
you can use a VNA or a directional coupler to measure the SWR.
73 Detlev
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Hi I used a nano vna v2 and nano PC program.
OK thanks for that Phil. I believe you asked a while ago if I had any photos of my modification removing the xtal oscillator and adding a feed for an external GPSDO reference? I had loaned my camera to someone but have it back now, so attached should be a couple of photos of the mod.
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Thanks for that, very neat! I have added an external reference lead to my Pluto c and connected my new Leo Bodnar. Worked flawlessly and very stable. So now ready for first QSO!
How’s your rig going? Had any QSO’s?
It seems to be working well, my main query is why, with the qro.cz sourced LNB, locked to the Leo Bodnar GPSDO, shows a frequency offset. For example, I tune to 10.489750 CW and the tune does not centre the beacon, it's pretty close, but certainly not spot on. I use the SDR Console software gizmo / trick to lock it to the beacon in the software. But with the GPSDO locking I wasn't expecting to have to do that, to be honest,
I have had quite a few good QSO's and seem to get pretty good reports. If you fancy a schedule my email address is good on qrz if you no longer have it Phil
Attached is how close the frequency is WITHOUT using the SDR Console software fix, but WITH the LNB LO GPSDO locked
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If I tune to 10.489749895 I am dead on the middle beacon. So what's that 105 Hz off? All told, is that considered OK for a GPS locked LNB and Pluto? I really don't know what to expect if I am honest....
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Hi,
The method I use is to measure the frequency offset that provides the Costas Loop Block of GNURADIO. But it needs proper scailing in order to measure Hz. I can measure at the same time the 750 QPSK beacon and if I want I can Tx at a free frequency and measure also mine. I Tx also BPSK similar to 750 signal but with random data. The values are compared to Doppler calculations. In previous tests Doppler calculations was outside GNURADIO. Now can included in it if desired.
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If I tune to 10.489749895 I am dead on the middle beacon. So what's that 105 Hz off? All told, is that considered OK for a GPS locked LNB and Pluto? I really don't know what to expect if I am honest....
Yes it seems similar to mine measurements.
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Hi,
My previous post regarding Doppler measurements... Link
Thanks for the link, if I am honest some of that was a bit too complicated for me, but I get the idea 😀
Would you advise I use the SDR Console lock to the middle beacon, or ignore using that and rely just on the LNB being GPSDO locked, as well as the Pluto for Rx? Thanks again everyone.
Every day's a school day!
