Hello,
Just read about this new CW transceiver.
Despite it looks similar to QMX, maybe the architecture and hardware is different.
Quite surprised the design and start of production went very fast.
A first review here:
Soon will find some of these on air, I guess.
73 Ignacio
Definitely different from a QMX. I see a few SA612ās and a 4.9 MHz crystal filter in thereā¦
Definitely different from the QMX: 3x the priceā¦
That had alarm bells ringing for me. Hans Summers from QRP Labs in 2017 wrote:
āThe last time I used an SA602 (a.k.a. equivalently as NE602, NE612 and SA612) was in 2003. It has poor IP3 and Dynamic Range. It was suitable in its intended application as a 45MHz 2nd IF mixer in early telecoms equipment. But unsuitable at the front end of an HF receiver.ā
Unfortunately, that is exactly where an SA612 is being used.
NE602 is used in the KH1. Just sayinā¦
I think its about using appropriate technology. Whilst not a customer for the CFT-1, I have recently restored an early KX1 which uses a similar architecture. The analogue receiver sounds lovely and the KX1 draws only 35mA on receive. I havenāt noticed the unsuitablity of the NE602 in that applicationā¦
If I were to use the KX1 in a contest next to my TS-890 Iām sure I could tell the difference, but thereās a place for radios that only sip gently at the battery.
Biggest problem with the NE602 and family is that they are out of production and have been for a few years now. None of the major parts suppliers have them in stock.
Looks an interesting rig but the price puts me off. I had a brief look last night.
The 602/612 mixer is used in all of my favourite rigs.
Hans is a clever guy and knows his stuff but I wouldnāt say that the performance of the QCX in the real world is much better than any other serious QRP CW rig. Certainly the lack of decent AGC in the QCX is something that many donāt like. The AGC option board is very crude.
I think the overall performance of the radio should be considered, not what components it uses. Remember that there was a lot of negative feelings towards the use of the SI5351 at first. Elecraft used the SI5351 in the cheaper, cut down KX3, the KX2 and all of a sudden the SI5351 was the magic answer to everything. The KX2 seems to have overtaken itās sibling in popularity.
Plenty in the FT817 too. Although not in the front end I think?
Wise words indeed. There are like a gazillion radios that use the NE602 in the front-end. Itās usually āgood enoughā. Itās an odd choice for new products though as it seems to have been out of production for quite a while. Of course it can relatively easily be bettered.
It looks interesting but Iām not sure about the price. Anyway Iām trying to downsize on the number of rigs not buy more. Though I could sell 3x QCX and have one of these. Or a QMX. Or aā¦
We do seem to be being spoilt for choice for CW trail rigs which makes learning how to scrape by on CW all those years ago time well spent.
Just by reading some responses of the creator (KM4CFT) in a YouTube video, seems this rig shouldnāt be compared with QMX.
He says the CFT1 wonāt do FT8 nor SSB, but itās been optimized for CW with a good AGC, a purposely designed easy user menu, that makes things easier for the activator, with main functions straightforward, like CW speed control and 4 programmable Memory messages in the panel.
The rig doesnāt have SWR reading, but the system is robust enough for some moderate swr variation in the field.
There is a mention of dealing well even in contest crowded band condition.
This is offered as a kit, partial or fully built as well.
73
Itās an old-school design like the Steve Weber radios and uses an IRF510 final rather than the usual the small MOSFETs. In other words, it might be the indestructible field radio I really need. Half the price would be better though! JS6TMW
I was one of the beta testers for this radio. If anyone has any questions about it, feel free to ask and Iāll do my best to answer. If I donāt know the answer, Iāll ask Jonathan.
E
As noted by others I believe KH1 and KX2 use SA612 as a convenient and effective product detector/BFO where dynamic range has been greatly reduced by the preceding IF stage and AGC, not as the first RF mixer where its performance is below switching mixers or DBMs. That said, as a first mixer these ICs work fine in many situations, best if you use a strong bandpass filter ahead and donāt expect to do contesting on crowded bands. They are unobtanium now, not recommended for new designs, so I hope they have a full tray.
It looks like HamGadgets has not published a schematic (can anyone find one?) so we can only guess at some the design choices.
Jonathon KM4CFT at HamGadgets is to be congratulated, itās a nice looking well thought out product, bringing something like this to the tiny and well-served ham CW SOTA/POTA market is a passion project, not a money spinner, and a yearās work or more.
Hi Paul,
The schematic of the CFT1 is included in the CFT1 Operating Manual available here:
CFT1 5-Band QRP CW Field Transceiver kit By KM4CFT (hamgadgets.com)
The KX2 does not use an SA612 or equivalent as far as I can tell though the KH1 apparently does. Itās an appropriate choice for a rig with a 1.2m long antenna.
Cheers,
Gerard - VK2IO
Ahh, found it, I assumed the operating manual would not contain a schematic but there you go! Schematic looks good, an old school design with the usual MCU, si/mm5351, a mix of SM, thru-hole and toroidal inductors, and using a backpack for the LCD frees up ATMega328 IOs.
Wonder how much power it does at 21MHz from the IRF510 and BF170 gate driver on 12v.
Sounds lively in Thomasā K4SWL review video. Nice work Jonathon KM4CFT!
Thanks to VK2IO & VK3HN for pointing out the schema that makes me notice the new rig has high pass impedance matching for the BPF.
Cheers, Pascal VK2IHL
Thatās some nice reverse engineering Pascal! I donāt know, youād have to ask the designer. It makes sense for the BPF to be designed for a 50r input Z and a 1.5 to 3k output Z to match the SA612 Gilbert cell mixer inputs.
The broad passband may be by design, given the filter is made of fixed value SMD inductors. Individual variations in components make a fixed narrow band filter impractical. We usually include a component of variable C (trimcap) or L in narrow filters to tune them āon the noseā. A handmade BPF with a -3dB bandwidth of say 200kHz rarely comes up right where you want it, and it only has to be 100kHz off for you to have an attenuator rather than a filter. If you design the filter to be 1 MHz wide you can drop the trimcaps without significant performance penalty. Thatās my guess, anyway.
PS: In your classical two resonator design I would force the C values down (<100pF) which will push the inductances up from nH to uH, which will be easier to make and possess higher Q.
