The nextion 2.8 "display is generating qrm, when I adjust the brightness control to less than 100 I have qrm at the reception, if it is 100 without problems. I installed a 5 ohm resistor in series with the power of the display, it was nice the brightness of the lcd.

?

73 de Júnior

And a correction to clear up any confusion: I wrote: " Clearly we need these transformers to be impedance matched in the circuit." It should have read: "Clearly we need these FILTERS to be impedance matched in the circuit". Wish I could blame autocorrect but it was lack of proofreading.

WA8TOD

John

It is 7:2 or a 3.5:1 ratio. The impedance ration is the square of the turns ratio.

I honestly don't know the answer to your question about paralleling filters. I guess you could try it..... but some bad karma and icky things might result. I would have to test it to be sure. If you are going to use a transformer anyway I would just adjust the turns ratio and use one.

WA8TOD

I don't think paralleling the filters will impact the nominal input
impedance of each filter.

If you have a SA and have something to generate a 45Mhz signal you
could sweep the filters in parallel and see what it does.

tim ab0wr

On Sat, 08 Sep 2018 12:41:16 -0700
"John KC9OJV" <greusel@...> wrote:

I rolled the dice on a pair of filters and received Toyocom 45E1A9Fs
which show up here
as
two pole filters at 1200 ohm termination impedance. If I parallel
those will I bring that impedance down to 600 and should that be a
goal? Should I try both in parallel? I do have a modest spectrum
analyzer to take a look at the results with.

John
KC9OJV

Should the pad after the balanced modulator be changed to add more loss?
That should be easy to do.

tim ab0wr

On Sat, 08 Sep 2018 12:39:46 -0700
"ajparent1/KB1GMX" <kb1gmx@...> wrote:

Warren,

1) 120 mVrms is far above the audio level that caused unacceptable
IMD before the filter mod. IMD must be checked and the audio levels
adjusted to make it acceptable.

The problem is the balanced mod easily takes that but the gain after
it means the 2nd mixer gets hit with a very high level.? With that
the output of that mixer is high and that leads to the next mixer
getting overloaded.? There is too much gain after the balanced mod.
This is why the balanced mod needs such a low input.

Allison

Warren,

Is that a 3.5:1 winding ratio or 3:5? Also to my previous question- does a 1200 ohm impedance filter become 600 ohm if you parallel two of them? I realize it narrows the BW but I've never seen information on the effect on termination resistance.

John
KC9OJV

jim,

input C for irf510 is in the 150-180pf range, drain to gate about 20pf.

Classic case for Triode miller effect.? Feed impendance must be low of you get the?
output voltage divided across the input 20pf and 180pf as negative feedback.
You seen this will all mosfets only the degree of it varies.

FYI the drain to gate C varies with DC drain voltage for all mosfets.

The circuit for the driver has issues:
Output impedance is not constant or low enough.
The stage voltage saturates (high emitter resistor)?
THe stage current limits due to high Collector L(transformer).
The 3904s loose gain with increasing frequency.

Allison

Daniel

You are receiving varied and solid advice in answer to your antenna question and I hope it helps.

Aside from that, as a new ham, I urge you to read through this board and be sure you understand some of the issues with the uBitx as it is delivered before you put it on the air. If you choose to go ahead and use the unmodified radio on the air, and many have and continue to do so, at least be sure you understand the ramifications of that decision.

Please ask questions on anything you do not understand and you will get immediate and enthusiastic response. Welcome to our hobby.

WA8TOD

[email protected]

Also the flower pot thing is a poor design and a only qualifies as a? better than rubber
duck antenna? for 2M portable.?

As to 6M vertical dipole is easier and only 10ft(2.8M) tall.

However for HF you need what you can do allowing for space.
FYI A cb atntenna is way to short for 20 (barely .26 wave at about 16.3ft).

While anything is better than nothing generally short antennas are inefficient
and need a good ground to work against.

Allison

More data for those interested. The first is a comparison of the onboard 45 MHz filter as supplied, with the eBay filter I have listed previously. This image was taken with the filters simply connected as is between the 50 ohm output of the spectrum analyzer tracking generator and its 50 ohm input. The blue trace is the filter supplied and the purple is the eBay filter.

The second image uses the same two filters but with a 2:7 turn binocular transformer on the input and a 7:2 on the output. The transformers are identical with the 7 turn windings connected to the filters and the 2 turns to the input and output. 7:2 is a 3.5 turns ratio which gives a 12:1 impedance transformation, matching the 50 ohm in and out to the nominal 600 ohm filter.

Clearly we need these transformers to be impedance matched in the circuit. It is also interesting to me how the center frequency shifts between the matched and mis-matched conditions.

You have not left the trailing part of the message you are replying so I am not sure what
you want me share ?

Raj

Kees,

I tried with and without R27. With R27 the 45MHz signal @ mixer drops a lot and only 6db without.
But the power out drops very little with or without. R27 reduces the spurs a little.

I had suggested removing the C22 and placing it there. I learnt a lesson the hard way.. the xtal filter
pin shorted to ground and the transistor failed !!! So the cap came back. I chose to place a 120pF
cap at C22 as that is enough to pass 45MHz without much attenuation. This RC roll off at 3 MHz
will be at least 20db.. I propose to replace the other coupling caps and emitter bypass with a
calculated lower value to attenuate as much below 30MHz as possible.

I think it will be helpful to have the 45M IF stage respond less to HF so that its pickup of the output
signal and amping it is further reduced. This the thought that brought out filter as quick solution!

The harmonics below 20Mhz is worrying me.

Raj

Ps Please leave in the parts that you are replying to! I read mails in Eudora and not on the web.

Richard Chan? If you are willing to work on 6m then this may be of a lot of interest in terms of a practical stealth antenna?



you can use a combination of a? 50mm coil former (see art.)? and a THIN modified surfcasting rod to produce a? 2.8mL ish dipole Stealth antenna for? 50 Mhz as per instructions.? you simply need a window or a port out of the building . Not necessarily a balcony.? ?

There are at least two off 6 m repeaters in the Toronto area,? based on my very quick web search.

uBitx can allegedly be conv to one band on? 6m,? but it is a big job.? Send a message to Mad radio modder and if he will talk to you you may be able to get the low down on it.?

A dipole perp to building facade is going to be? a HELL of a LOT? more efficient than some magnetic loop inside.

Farhan

I am not sure I understand the statement: "The IMD is not a major challenge on the TX side as the signals are at a consistent amplitude. Hence, the filter is on the tx side alone."

In both cases of use of the bi-directional amplifiers one of the two signals being mixed during TX originates in the SSB generator and, by definition, is both of highly inconsistent amplitude and is very susceptible to IMD whenever it encounters non-linearities. Is this really what you meant to write?

WA8TOD

开云体育

That seems to be a British version of One of the ones I’ve used. ?It should work fine. ?I would expect that it has a toroid-based pick up system inside. ?

I was thinking about an Albrecht SWR 20 which I can see that is used only for CB. Do you think it should work for 20/40m band ?

开云体育

Show us a photo of the swr meter you’re considering.?