Posts by SV1BDS

  • Bandpass filter

    Hi, also some thoughts more.

    A hi power filter is more expensive than a low power one. Also if you put a filter before the PA you do not amplify harmonics so you get more useful power. One another more benefit to put it before is that you prevent creation of self oscillations especially if you have a lot of cascaded gain at same frequency. You must take care not to overdrive the PA as it will be harmonics created. If the PA has a power sense meter this is not always measuring real output power !!! In my case the power sense output is display more voltage from one value and more but only harmonics are produced !!! No more power!!! The usual filter that can be at the output of a PA is a low pass one as it has less loss. You need one if your harmonics are more than 40 dB than the carrier. If you have a lot of cascaded gain it is a good practice to put a BPF between every stage. In my case I have about 55 dB cascaded gain (* 500.000 !!!) without self oscillations. Also very very good shielding is required.

    I hope that all this help ...

  • MY QO100 SETUP

    Hi i2NDT , does the amplifier amplify small signals without applying anything to EN input ? Normally without any input at EN must work and applying gnd or Hi is disabled. Can you ask also the supplier of the pcb for instructions regarding this pin?

    UPD: next to the 5 pin chip is a LED. May be this is an enable LED. Is this lighting ? Is this connected to the EN SKY's ? What is the voltage of the EN SKY's ?

  • No more power from this PA

    Hi,

    Some proposals to check:

    - How is the voltage across 510 SMD R ? (you measure the current via the ohms law)

    - Verify that input attenuator is OK (measure without RF & DC power the 3 resistances )

    - Verify that voltage is at hot end of both green chocks without appling input RF power.

    - Connect dummy load, DC & RF input of a few MHz and use an 1N4148 and a 1nF capacitor as an RF probe

    to verify power at 1) attenuator input, 2) attenuator output, 3) between amplifiers, 4) output

    - Verify that a few volts exist at input pin of final amplifier without RF input

  • MY QO100 SETUP

    Quote from SV1BDS

    Hi,

    A green dual Octagon LNB was modified for 25 MHz external reference. A damage was occured while opening it , a 78L05 was broken and it was replaced adding also a jumper wire as the PCB was removed. The L was added near the F connector and the C at the removed Xtal 25 MHz. The connection is with a teflon wire wrap cable. I was lucky and it was a single crystal one. About 3 dB SNR improvement was noticed. Also noticed a IF level increment of about 5 dB. The second output is ready for WB usage...

    Hi, maybe the 25 MHz must connected to the other xtal pin !!!

  • MY QO100 SETUP

    Hi,

    A green dual Octagon LNB was modified for 25 MHz external reference. A damage was occured while opening it , a 78L05 was broken and it was replaced adding also a jumper wire as the PCB was removed. The L was added near the F connector and the C at the removed Xtal 25 MHz. The connection is with a teflon wire wrap cable. I was lucky and it was a single crystal one. About 3 dB SNR improvement was noticed. Also noticed a IF level increment of about 5 dB. The second output is ready for WB usage...

  • QO-100 TRANSVERTER FOR HF TRX

    Hi, 4Z4LS

    Also I wanter how you can archive suppression of Lo and image. A less complicated Lo could be a ADF4350. Do you have capability of external frequency reference from GPSDO? You have an amplifier before the LPF at 2.4 and you amplify also the 739 signal.

  • MY QO100 SETUP

    Quote from iw5bsf

    hi George , looking on the internet 2012 RA3WDK pipe filter 3cm loss 2.5 db

    73 Roberto

    Hi Roberto, one of the probes was not fully inserted. After fixing it 2.5 dB loss is now archived.

    Thanks !!!

  • MY QO100 SETUP

    Hi, Roberto, I wish everyone a happy new year !!!

    It seems that I use the proper probe length. Maybe I have to investigate more why I loose 1-1.5 dB more. In these frequencies it is very easy to loose such power very easy. I also must cerfully measure it again. Thanks.

    The target is to test a non LNB solution. I expect some ERA1 from eBay to do a *3 Lo from a ADF4350. The mixer exists and in shack looks promising. Inside shack for testing I receive 10.6 GHz from LNBs Lo when antenna looks at the window !!! What I expect to see is the SNR of the CW beacon that it will be archived.