Mike,

You solved the source issue....

with the counterpoise as suggested I did say the SWR will likely change.
Generally the 1:9 scheme is problematic for RF in the shack unless you have
luck or resort to choking...

You might try a End fed half wave as when the wire is tuned you will have less RF.
Also if the bands of interest are the 40/20 there are a few that do them well.
Though a town home is likely a noisy are a for 80/75M.??

However that picture scares me...? ;)

Allison

This is primarily an SSB transceiver, and harmonic suppression seems adequate in
that mode on the stock rig.? Best and easiest fix is probably to either not use CW mode,
or do a minor hack to move the CW mixer injection an earlier mixer so the 45mhz
filter takes out the harmonics?as previously stated.
?
The uBitx relay arrangement is not that uncommon, though would be better
to double the relay count and use separate relays for input and output.
Board layout is important.? This guy definitely knows what he is doing:
? ??

Another solution might be to get an outboard set of filters such as the WA2EBY fllter board:
? ??

LPF's such as seen on the uBitx are usually adequate for use with class C amps
on CW transmitters (which are dealing with high power square waves).??
However the uBitx gets by with as few LPF's as possible by covering multiple
bands with each filter.? The corner frequency of the LPF may be a bit high to?
fully suppress the harmonics of the lowest band of that set.

Jerry, KE7ER

Iz oos,

TLTs can be made with low loss.? ? However making a matched set may be harder
as they have to have the exact same phase response.

Also the 1:9 is 450 ohms? (50*9).

Allison

Make sure you have adjusted the BFO to the correct frequency.? The carrier will drop.

Allison

Allison

Have you shared your past findings here? I did a search and found nothing but I could have missed it. It would seem to me that if you knew the product was illegal for use on the air you would have a responsibility to share that with the group.

WA8TOD

Warren,

Latching relays have a higher cost, I like the idea though.? However there are lower power
relays that would do the job.? Since the radio eats power on TX anyway another 200ma is tolerable.

I would want band pass before the TX chain.? The logic is you get cleaner out if you put cleaner in
and it wold fix many of the spur issues.? However that's a lot of relays or diode switching for 9 bands.

Allison

Arv,

For bitx20 (or 40) a monoband radio traps and Caur filters are a good solution.

For a multi band radio its a spot solution that is likely to case troubles on other bands.

The fundamental issue was inadequate to non existent filtering for the TX path
before the TX.

Allison

Warren,

In my testing I also found the isolation across one relay was barely 45db in one configuration and 50 in another.
Using one relay to switch both ends of a filter will compromise the filter attenuation characteristics.

Most other radios commercial put a spdt relay at each end to avoid common mode and coupling.

You are seeing what I saw....

Allison

I am not sure Arv. The real solution here is like a "fork lift" upgrade, replacing everything after T11 in the transmit chain. If I were doing a redesign I would use the same four filters, add five more relays, and decode the three lines to get four lines each driving the pair of relays bracketing the desired filter.

BTW..... in re-reading this, unfortunately after it was posted, I note that my threshold line is set at -53 dBc rather than -43. In your imagination move the green line up one division. It does not change the outcome or the analysis.

WA8TOD

No one is going to want to hear this but the design of the PA output filter is probably fatally flawed and it is likely due to board layout issues.

I have been puzzled how the high order harmonics of 80 meters, for example, could possibly survive a 7th order filter which should have well over 50 dB of attenuation at the 5th harmonic. So today I set out to test the results with a 9th order filter, figuring more is better. The harmonics remained. But in troubleshooting that installation the source of the issue was revealed.

In the attached screenshot the purple trace is the 80 meter CW output with the harmonics clearly far in excess of the green -43 dBc legal threshold. The blue trace is the output with L20 removed which disables the 80 meter filter and blocks RF output from the finals from reaching the output connector. (Don't worry..... the tests were carried out with the drive reduced so the output was only one half watt. And I have a bag of spare IRF510s on hand......). The harmonics remain! How can that be?

Pic #2 shows the path 80 meter RF follows through all three switching relays in order to reach the filter. It is a very novel and inventive concept to use three relays to switch both ends of 4 filters. Most manufacturers would require 8 separate relays to do this job. And for a very good reason.

In order for a filter to provide the required 50+ dB of attenuation, the filter itself must have 60 dB or more of input-to-output isolation. If it does not then the unwanted products simply bypass the filter and go directly to the output. That appears to be exactly what is happening in the filter complex of this unit.

There is no easy fix for this. No amount of on board filtering and tweaking is going to improve harmonic suppression until the path around the filters is blocked. I suspect that path is via the relays themselves but board layout often is critical as well in such cases. My guess is the only solution would be either extensive external filtering or a carefully laid out daughter card to replace the existing filters and relays.

WA8TOD

Check my website, for details, but I now have a completely drop-in Raduino clone available in kit form for anyone needing a replacement for a damaged Raduino that they are otherwise unable to repair or just wanting to have a spare on hand.

It's being offered as a bare board, a complete kit of parts INCLUDING the NANO which will be pre-programmed with Ashhar Farhan's latest factory software from Github (Currently v4.3) or , for a slightly higher price, the kit version is being offered with the Si5351 already soldered in place and continuity checked to insure the connections are good and there are no shorts between the pins.
This card has some extra bypassing capacitors, the 4.7K CW pull up resistor can be directly mounted on the board (or if you are replacing an existing Raduino installation and have already wired it to your key jack you can leave it off the board).

The 7805 regulator has been mounted flat on the rear of the board with a heat sink and input dropping resistor so it runs much cooler.? The clone is just over a centimeter wider than an original but the display mounting holes have been kept to the exact same pattern so that a normal 16 X 2 parallel display will mount properly.? The display is not supplied with the kit to keep the cost lower as most users already have one or more on hand anyway,.

The pre-programmed NANO? will be supplied with the pins loose and not installed so the user can mount it either on the front (not recommended) or on the back of the card to keep it out of the way of the display in the manner of the current factory supplied Raduino cards.

Any software that currently runs on an original Raduino will run on this card including the KD8CEC versions.? (That includes CEC's Nextion enabled versions as well).

The construction manual, pictures of the board and ordering/availability information can be found on my website

Jim Sheldon, W0EB

Hi all. I don't know how to suppres great carrier in TX mode.

开云体育

Hi Allison, these 1:49 transformers are just conventional transformers. Would you think that a 1:4 and a 1:9 current (not the voltage ones) transmission line transformers in series to get a ratio 1:36 would be too lossy as I think or may be used? In that case the transmission line of the 1:9 transformer is just 150 ohm which is theoretically too low.

Again, thanks for the explanation.? After adding the air choke and counterpoise (17.5ft -- I'll trim it back tomorrow), the uBITX now behaves properly when keying the mic and transmitting CW!!!

The SWR is a bit higher, though.

Also, it has moved a bit toward the Frankenstein's monster end of the aesthetic spectrum.


73 Mike KK7ER

No it wasn't. Arv just created the antenna group today. The loop group you're talking about is different.

Vince.

--
Michigan VHF Corp.