Keyboard Shortcuts
Likes
- BITX20
- Messages
Search
Re: BITX QSO Afternoon/Evening, Sunday, August 5, 3PM & 7PM Local Time, 7277 kHz in North America, 7177 kHz elsewhere.
If conditions are suboptimal, could we maybe CQ BITX by FT8 on Sunday evening?? I'm new to the mode, so I don't know if that's appropriate.?? But I think the first TX would be (for me) CQ BITX W0RVO EM59, right?
|
Re: Interesting antennas for QRP
Allison,
toggle quoted message
Show quoted text
I haven't messed with it, but Kees' AQRP VIA includes the following feature: "Calibration data (Open/Short/Load) is captured and recorded for all frequency steps between Start and Stop Frequency. This allows data to be recorded at the end of a transmission line, effectively eliminating the coax from the computed and displayed data. These data values are sent to the PC when requested." That could avoid lots of trips up to the roof.?? Though I'd tend to do a direct measurement to confirm that measurements via coax are accurate enough.? Jerry On Fri, Aug 3, 2018 at 09:56 AM, ajparent1/KB1GMX wrote: What I've done is make a bridge and actually measure the antenna wire and its pretty interesting |
Re: Interesting antennas for QRP
That's worked for me at least.
Of the wire is already trimmed for say 14.2? changing the transformer should show a different SWR for the real feed point resistance.? Resonance should not change for different transformers save for internal wire lengths.? ?Of course we can tweak the wire to mask that but resonance suffers and coax shield currents rise. What I've done is make a bridge and actually measure the antenna wire and its pretty interesting how it can vary with height.? That was an exhausting project due to need to drag gear to the yard and build and validate a remote bridge.? Lots of up and down, batteries, and no small amount of retesting to validate results. Allison |
Re: End Fed antennas w/ uBITX
#ubitx
On Fri, Aug 3, 2018 at 10:43 AM, Warren Allgyer wrote:
The fact that the antenna you have has resonances that fall at integer multiples says there is something else going on there. I suspect this is the function of the 6 turn inductor which would have the effect of electrically lengthening the wire, and lowering the resonant frequency, with greater effect at successively higher harmonics of the fundamental.You pretty much got it.? That is how Danny (myantennas owner) explains it in a blog post at .? I referred to it way back in post 54967 but at the speed this thread was moving then it was easy to miss. -- |
Re: any tips for debugging RFI issue?
#ubitx-help
The SWR may be good with the wires in use but you have an off center fed antenna and RF on the coax is not much better.? ?? For both grounding the braid and using a Air or ferrite choke at the ground point to the radio is advised. Using a choke at the match box will require a counterpoise to be used or the antenna may be ineffective. I also expect the SWR will change.? You need a .25 wave counterpoise with that matchbos and the coax is not a good choice to do that service for the problems you are already having. Your likely have a lot of RF on the coax and that is a source of the problem. You are up against the wall (townhouse and all) for antennas and I get that.?? Things to try... First and foremost use a counterpoise wire at the matchbox they provide a lug for that the hanger hook is that in the picture.? ?The wire should be around 16.5ft for 20M. Try attaching to the radio chassis itself a wire maybe 16-17ft (quarter wave) to force the case to a current node (sorta ground).??Just lay the wire out straight on the floor or ceiling (if ground floor) as a test.? See if that helps 20M (likely makes other bands worse) One thing you might try is replace the matchbox with a vanilla 20M center fed dipole (two 16.5ft wires) even if temporary.? If your high enough one of the wires can just dangle (forms a center fed inverted L). Or replace the matchbox with a 1:49 type and use a 66-68ft wire (half wave end fed and working on harmonics) You may still have RF on the coax but a lower magnitude and maybe less troublesome. Also make sure the board and the connector are electrically connected to the metal case, try putting the cover on as well but external wires will need to be choked with ferrite. For 1:9 baluns there are a few magic lengths that work better for some bands or all. table attached has that info. Also that arrangement in the all band form requires a tuner at the radio as not all bands will match well. A tuner does not help the RF in the shack issue, its there ot keep the final intact. Let us know her if and of it helps.? I;m sure there are others having similar issues. Allison |
Re: Interesting antennas for QRP
Allison,
I can't speak for others, but the reason I use squares of integers is because I can do the math in my head:-) You are right, no reason why it can't be a different ratio, just means trimming the antenna length a little. Still, it would be best to keep the length of wire close to a theoretical 1/2 wave length for best efficiency, I would guess.Anything in the 1:36-64 range should be good for the transformer. Joel N6ALT |
Re: Front Panel Stereo Socket Board Wiring Layout
Sunil, Thanks for the update. An issue: I found on my front panel PCB that pins 2 and 5 on the headphone jack were not connected together (tip and ring), so that I only heard audio in the left side of my headset.? I jumpered those two pins together, and now I have audio in both sides.? It still properly disconnects the speaker when the headset is plugged in. Have you made an update to the front panel PCB, since I received mine (a few weeks ago)? Connector discussion: I ended up ordering and using a Dupont kit for the female bodies/sockets and right-angle pins.? They worked OK, but the volume connector hits the main PCB standoff, and the mic connector is a very tight fit against the chassis-mounted round 4-pin XLR connector body. Would the TVS connectors be lower-profile?? Suggested US source for those connectors?? Any model/order numbers? I got my Dupont kit: and Inwiss crimper tool: . from Amazon US, free two-day prime shipping. We have a group of folks here that ordered a quantity buy of uBitxes, and some have ordered and/or received cases, but I'm one of the first to actually assemble one and get it on the air.? We are having a meeting in September to address uBitx build hints and kinks, and I'm putting together a log of issues/fixes to help them get their uBitx boards up and installed in cases properly.? I thought to share my Dupont kit to anyone that needed connector shells and sockets, but if a TVS kit is better, I'll go that route.? So far, searching for TVS connectors on Amazon hasn't turned up a kit similar to the Dupont connector kit I have. There's another thread on here with my notes, in case you've not come across it, yet: Volume control connections: I figure I'm not the only person that even after doing some head-scratching trying to figure out which pins where the 'high" and "low" pins on the volume control, that I managed to get it backwards, and was rewarded with a VERY load noise when I first powered the radio on with the control turned completely CCW.? It would be helpful to have a photo of the actual back of the volume control, showing which pins are "high" and "low" ("mid" is hopefully kind of obvious). XLR Mic connections:? There is no information as to which pins on the XLR jack are to be assigned to Gnd, PTT, and Mic.? I did a Google search, and found a few which seemed to agree that Pin 1 is GND (natch), and that Pin 2 is Mic, and pin 3 is PTT.? At least that's how I wired it.? I haven't found a pre-wired 4-Pin XLR mic to try, but it appears that Cobra CB mics were wired this way, and there may be some some of industry standard for wiring 4-pin XLR PTT mics, but I haven't found it. Thank for all your effort to bring us a really nice case for the uBitx.? Mine is dark green, and sets off the green LCD display nicely. 73, -- Dave, N8SBE
|
Re: Interesting antennas for QRP
For some reason there is a religion for squares of integers 6/7/8 yielding
one to 36, 49 and 64. There is no reason why the winding could not be 2t:13t for 6.5 turns ratio or 1:42.5 or 2 to 15 turns for 7.5 ratio or 1:56.25.? The latter? would match 2813 ohms well. Transformers can be used in a compound series arrangement like to 1:9 in parallel for primary and series for secondary to get 1:36.? Many other possible configurations can be configured. Allison |
Re: End Fed antennas w/ uBITX
#ubitx
With a short coax, I saw the same pattern of VSWR peaks and troughs as a long coax,?
toggle quoted message
Show quoted text
just that the peaks were higher with the short coax.? As expected. ? On Fri, Aug 3, 2018 at 08:43 AM, Warren Allgyer wrote: If I could the VIA plots of the transformer/antenna with a very short cable, and again with the operating length cable, I could know which low VSWR points are real and which are simply created by loss. Short of that, if it makes contacts and the toroids don't explode (some have!), you are good to go. |
Re: Interesting antennas for QRP
There are some general reasons for that.? One being the 1:64 transformer is more difficult
and most installed wires are at a lower height so the feed point resistance is lower. Also 50*49 is 2450,? 50*64=3200? most wires are in that general range such that there is overlap.? ? If the wire is thinner and higher the 64 transformer may be better but for most installations the 49 will do fine. Also 1:36? (50*36=1800) is a doable transformer (2t:12t wire) as even for a nominal 2500 ohm wire the mismatch is 1.4:1.? And low wires as would be typical for field installs at lower frequencies like 80 and 40M are lower in feed point resistance. Allison |
Re: End Fed antennas w/ uBITX
#ubitx
Seems that most EFHW impedance matching transformers are wound on ferrite or powdered iron cores.? For experimental purposes it should be possible to use air-core (PVC or Acrylic, or wooden cores) transformers.? The number of turns for a given inductance is not that much different between metallic core and air core transformers.? This is especially true if the air-cored units are wound on toroidal forms.? Those with a lathe could easily turn toroidal formers from wood or plastic. Possible advantage of winding one's own matching transformers is that modification and adjustment of impedance transformation is more easily done if the transformer is not potted inside a plastic box.? Winding one's own transformer might also allow connection of a variable capacitor in parallel with the antenna side to make it into a end-fed wire tuner (L-match) to achieve a more perfect match Arv? K7HKL _._ . On Fri, Aug 3, 2018 at 8:24 AM Jerry Gaffke via Groups.Io <jgaffke=[email protected]> wrote: Warren, |
Re: End Fed antennas w/ uBITX
#ubitx
Warren Allgyer
Got it Jerry. I read your voltage as peak to peak rather than peak. My bad. If I could the VIA plots of the transformer/antenna with a very short cable, and again with the operating length cable, I could know which low VSWR points are real and which are simply created by loss. Short of that, if it makes contacts and the toroids don't explode (some have!), you are good to go. |