News, Updates and Other Minutiae
November 2024 Phillipe F6ETI has done some serious testing on the Noise Canceller and shown it works up to 72MHz and is usable with some loss at 145MHz. Links to his website with photo's, video's and description of the testing on the Noise Canceller page.
September 2023 Long time between drinks, but not much happening on the tech front at the moment. Added another couple of rants to the rant page.
January 2023 Updated the AD9833 VFO code to use a 12F1840.
December 2022 Added rant about todays useless (internet) search engines.
November 2022 NEW Project An AD9833 Based Simple VFO. FT101ZD VFO project updated.
October 2022 A replacement internal DDS VFO for FT101Z/ZD rigs. Because the worlds postage system has gone totally bonkers and it is not possible to send a small pcb anywhere except at extreme cost, I am slowly making available the option to purchase pcb's from Pcbway. First up is the Simple DDS VFO 2017 project pcb. Others will be added over time. Noise Canceller kits available again- see Noise Canceller page.
Privacy Policy uploaded. GPDR and all that stuff In accordance with various bits of legislation around the world, either currently in force, about to come into force or proposed, you will now find that annoying "We use cookies" notice at the top of this website. The full Privacy Policy is available at the Privacy Policy link in the footer at the bottom of the page. (If you don't know what GPDR is, Google it. Real scary shit for ANYBODY with a web presence.)
This is a filter/leveller for use after an AD9850 DDS module, from G3OAG. I will let him explain the circuit in his own words (edited and condensed from our email conversations).
G3OAG DDS Filter/Leveller
I have worked out that levelling the DDS output can be achieved with a simple high pass filter. My DDS, using an e-Bay module and 2N3904 amp stage, gives me 10.3dbm at 10.8Mhz (1.8Mhz + 9Mhz offset) down to 2.3dbm at 38Mhz (29Mhz + 9Mhz )...a difference of around 7.5dbm. Up to now, using a simple T design, three pole high pass filter, I have achieved some degree of levelling with 2 x 470pf caps in series and a coil of around 0.1uh in the middle. This obviously lets the higher frequencies pass relatively unattenuated, and the lower frequencies are attenuated so that at the output of the filter, the level is getting on to the same level as the higher frequencies. After further experimentation, I have ended up with ten components after trying three previously. You can see the output of the final 2N5109 amplifier and splitter for the two DBM's is within 1db across the nine bands. I do not think this circuit is totally repeatable, as there will be various capacitance and inductive differences between different builds. I ended up having to use a damped trap ...the 1.58uH coil and the 150pf with the 220 ohm, to lower the 160m output which as you know is very high compared to the 10m output - in this case a range from 10.8Mhz to 38Mhz owing to the 9Mhz IF offset. However, it seems to function OK, and I'm sure other builders can make the necessary changes.
The amp following the e-Bay DDS board which uses a 2N3904, is from the LU5DJV DDS circuit, but they are all similar. This outputs around 10.5dbm at 160m (10.8MHz with the 9Mhz offset) going down to around 2.3dbm at the 10m band...38Mhz. The amplifier following my filter is the standard 2N5109 Class A design, originally in the ARRL Handbook, which has been used everywhere, and gives around +17db to +20db gain. This feeds a power splitter, which gives two equal outputs to feed both the receive and transmit mixers. I was hoping to get the magic +7dbm out from each output, but owing to losses in the filter, I am getting around 5.5dbm...not that it will make much difference. Below are two photos of my DDS and the filter, which is crammed onto the board. The two chips at the top left are 2x ULN2803A which are the drivers for the band relays in the RX input filters and the PA output filters, and also for the mode switching. You can also see at the bottom right the ancient Hatfield 3320 splitter and the two SMA sockets which feed the RX and TX mixers. This is the VU2CNS DDS circuit which works well. This DDS will go into my homebrew 20w rig which I built years ago and which currently uses a Vackar VFO and which I've had hundreds of QSO's with. My new build DDS will go into a new rig.
