Date   
Re: #ubitx Power output on 40 / 80 m with high current levels #ubitx

Alex - PA1FOX
 

Thanks John and Jerry for the supportive comments. Here are some replies:

Are you sure you are using SSB? And the amplifier class is really AB? Remember, SSB output is Pk-Pk, while AM is "100% modulation". I would be interested in
seeing if there is any carrier output. This sudden current jump is suspicious of extra oscillation.

Yes, I am using SSB but also can switch to CW. With no modulation in SSB there is no carrier. Well there is if you listen on a nearby receiver but it does not give any output on the power meter. Suppression seems ok. I think I was not clear in my explanation about the current. There is no sudden jump when the modulation sinus is increasing graduately. The gain seems quite linear and with the mic attached the voice sounds quite nice. During the building process I did encounter some spurious oscillations but managed to get rid of them by proper decoupling and repositioning of the toroids. The jump in current I meant was when switching from 40M to 80M. At 80M I get 5 watts RF with about 3A current. The rig in TX mode with no modulation runs about 0.75A so the IRF's are taking the remaining 2.25A at full modulation.

Today I finished the second LPF and this gives more interesting information. Overall gain of the TX chain decreases dramatically when tuning from 80M to 17M (my current highest band with LPF). The following occurs:

80m: 5 watts 3A
40m: 5 watts 3A 
30m: 1.1 watts 1.4A
20m: 0.2 watt 1.04A
30m: 0.25 watts 1.06A

If I turn RV1 for more TX gain I can increase the power output on 20m to 8 watts at 2.6A
On 30m I can get 8 watts at 2.5A after setting the right gain with RV1.

Don't go above 3v or so on the IRF gate. Maybe even 2.5v. These are very touchy devices and hit a full on current condition with no warning...as you have
already found out.

Correct but these are not adjusted by RV1. I have built the 'original' uBitx version where RV1 is between two 2N3904's. in the block before the 2N2219's
The optimal bias for the IRF's in my rig is around 2.8 volts. I can adjust both bias pots so that the second harmonic is minimized which is normal.

IRF MOSFETS are notorious for being extremely variable. You are right that a different batch will give entirely different results. The use of #10 material for the toroid is very good, but I would increase the size to at least a T50, and probably would go to a T68 or even a T100 for high power levels. It doesn't take much to saturate a T37, and then the transformer is an entirely different one. Also, it might be prudent to look for a different form factor for the output transformer, one with a bit more shielding than a toroid. I know, they have a good
reputation, but they are not perfect in a strong RF field.

This is true when the T37-10 is saturated at high power. Changing the size should not have influence if I would hold the measurements in the say '1 watts' range.
Note, I am not trying to pull maximum output power of the IRF's. I would be glad with 6 watts but with a good PA effciency. 2A overall rig current would give 1.25A for the IRF's
At 12 volts this would be 16 watts power input and at 6 watts output for a class AB amplifier this would be nice. It does seem to do that at the higher bands.

It's unlikely that the bidirectional amps have much to do with radiated power...provided the throughput is adequate. In the case of the BITX, that is roughly 10 dB.
Know also that the IRF510 is not a very good device above 40m. Yes, they can be made to work well, but it takes a good impedance match and heat control to
do so

Well the overall gain of the TX chain is not the problem, it's frequency dependant. at 80m there is some 10dB more gain than at 20m. 

There is however a solution to that. I will use three LPF's (as opposed to two LPF's in the original schematic) and these are selected by two relays. The logic table for the two outputs from the arduino are:

00 :   no relay activated, 80m and 40m LPF selected
01:    relay 1 selected: 30, 20 and 17m LPF selected
10:    relay 2 selected  15, 12 and 10m LPF selected (yet to finish)
11:    not applicable

I could use the relay1 activation line to increase the TX gain at some stage. Or use '00' to reduce a bias setting of one of the TX preamps. This way I could adjust the overall TX gain in three steps and compensate for the gain loss at higher frequencies.

The thing that bothers me most currently is the high current at 80m and 40m. With 3A at 5 watts maximum a lot of power is used to heat up the sink. Not good when running portable (although handy to keep the hands warm in case of winter SOTA ...:)

Jerry, I will try the 10 ohm resistors in series with the IRF gates. Have not tried that yet, thanks.

And I will dig into the article from WA2EBY. More knowledge and theoretical background will help. I've built a lot of VHF amplifiers but not yet in the HF range which 'normally' should be simpeler. Unfortunately I don't have a spectrum analyzer (yet) but I ran some test with the frequency counter connected to an RF probe near the LPF coils. The counter always displayed the correct frequency. I did not hear strange things on my Icom rig when tuning over the bands as well.

To be continued...

73, Alex
PA1FOX





Re: #ubitx uBITX keyer change #ubitx

Gordon Gibby <ggibby@...>
 

I got my CW working pretty reasonably.  I did all the changes below in John Pieper's suggestions.

I also took out a write to the serial port that I thought might slow things down.

I took out the 5 mSec delay.

And I altered the "numbers" chosen as the dividing points between dot dash  both  straight key.   By my calculations you can increase the both to a much higher number, like 240 or so, and that makes the straight key much more likely to work.

​The Key I was using was also pretty lousy and that may be the remaining problem.


I'm having problems with the "core.a" "unable to rename" problem.....that really slows me up....Even when "administrator."   Any solution for this?


Now I need to figure out exactly which of the above changes made the most difference.


Also---in the photos on the Wire up of the uBitx  he is connecting the resistor to the RING, not the tip.   At least it looks that way to me.   I think you want it connected to the TIP.    I had to pull my plug out slightly to make things work, which clued me into this.  



Darndest thing --- I discovered a SHORTED patch cord of coax when connecting up to a dummy load.   Never saw THAT before....



Gordon




From: BITX20@groups.io <BITX20@groups.io> on behalf of John Pieper <j.pieper@...>
Sent: Friday, December 29, 2017 2:29 PM
To: BITX20@groups.io
Subject: [BITX20] #ubitx uBITX keyer change
 
I was disappointed by the performance of the built-in keyer code in the uBITX when using my paddle. In particular I was having a hard time getting the first code element of a character to come out, especially if it was a dit. It made the whole thing seem clunky and basically unusable. Looking into the code I quickly spotted the likely cause. Near the beginning of cwKeyer():
//if a paddle was used (not a straight key) we should extend the space to be a full dash
//by adding two more dots long space (one has already been added at the end of the dot or dash)
if (cwTimeout > 0 && lastPaddle != PADDLE_STRAIGHT)

    delay(cwSpeed * 2);
This is trying to enforce character spacing, but has the effect that between characters the paddle is only sampled once every two bit times, making it quite unresponsive. My opinion is, let the operator produce the correct character spacing, make the paddle as responsive as possible. I took out those two lines. I also took out the 5 ms delay below, right before the continue statement. Now the paddle is always being sampled at a high rate and the feeling is much smoother. This seems usable now.

While I was in there I also took the opportunity to insert a 10 ms delay after the calls to startTx() and updateDisplay() (lines 120-121), but before the end of the conditional block. This gives the T/R changeover time to settle before the key goes down, so that an initial dit won't get cut off. Finally I redefined CW_TIMEOUT to be a multiple of cwSpeed, so that faster code speeds can have shorter timeouts. 600 ms was way too long for me. I used 7 times cwSpeed; maybe that can become a setting at some point.

73,
John AD0RW

Re: No TX #ubitx

joe kallo <quietglow@...>
 

Just got home from work and checked: brown wire properly hooked up. I measure 13.5v to the heatsink  w/o the key down and ~13v with it keyed.

Re: No TX #ubitx

Gordon Gibby <ggibby@...>
 

​rats.   wished it could have been something simple.....

sorry.....




From: BITX20@groups.io <BITX20@groups.io> on behalf of joe kallo <quietglow@...>
Sent: Tuesday, January 2, 2018 6:10 PM
To: BITX20@groups.io
Subject: Re: [BITX20] No TX #ubitx
 
Just got home from work and checked: brown wire properly hooked up. I measure 13.5v to the heatsink  w/o the key down and ~13v with it keyed.

Re: Tuner? Well Sure!

Mansueto Grech
 

Hi Gordon,
Fantastic idea.
I would be interested
73's
Mans. 9H1GB

On 29 December 2017 at 16:05, K9HZ <bill@...> wrote:

So after finishing up most of my projects a few days ago… I really needed something to do… so I put on the drawing board… a 100w automatic tuner that can work with the uBITx (intended to go inside the same case actually) that provides power, SWR, band memory for same antennas, low power tune, bypass, etc. all in a kit form for about $30.  I’m prototyping the think now and will work on the tuning/communications code (to integrate into the Raduino) shortly.  I’ve contacted a few of you off-channel to work out some protocol/communication issues…  but Stay tuned (double play on words there)!    

 

 

Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton – J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com

Like us on Facebook! facebook icon

 

 

email:  bill@...

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Gordon Gibby
Sent: Friday, December 29, 2017 8:21 AM
To: BITX20@groups.io
Subject: Re: [BITX20] ALE, WINLINK and uBitX

 

Good pickups!

 

So the ALE (automatic link establishment) crowd, much like the WINLINK crowd, tend to use LOTS of bands....and thus they find ways to make their antenna systems work on mulltiple bands.   Here are some of the most popular ways:

 

1.   Fan Dipoles (time honored technique of tying multiple dipoles together at the CENTER, and the energy tends to go to the correct one, since all the others present much higher impedances.   The wires "fan" out with usually wooden spreaders at the  end and some string involved to keep them somewhat separate.   Been there done that many times, my college ham club has a 3-band unit up on the top of an 11 story building rightnow that I built for them.   Build for yourself, dirt cheap. 

 

2.  Auto-tuners  --- everyone makes these now and many can tune as soon as they see RF, or even return to previous settings that were memorized.   LDG,  and others.   Low power versions for $100   End fed wire to balanced line fed dipoles---they work with lots of different kinds of wire. 

 

3.  Inherently multiband antennas:   example, full wavelength loops.   Build for yourself.   

 

4.  Carefully tuned end-fed transformer-fed antennas --- there are now several of these on the market and they give an acceptable SWR on mulltiple harmonically related bands.   Tend to be close to $100

 

5.  (the one I dislike)  resistively terminated folded dipoles --- these use a resistor to make up for what a folded dipole can't create and give an SWR that is "acceptable" literally across EVERY FREQUENCY in a decade of frequencies.   3-30 MHz.   The tradeoff is loss, as much as 10 db at times.  And they generally are pricey.

 

6.  There are some multi-band vertical antennas on the market that are basically vertical fan dipoles, but scrunched up in a nice package.   An elderly ham in my city has one, 32 feet tall....a gang of us put it up and doggone it does from from 40 meters all the way through 6 meters

 

 

And there are probably many more....

 

Gordon


From: BITX20@groups.io <BITX20@groups.io> on behalf of Arvo KD9HLC via Groups.Io <arvopl@...>
Sent: Friday, December 29, 2017 9:12 AM
To: BITX20@groups.io
Subject: Re: [BITX20] ALE, WINLINK and uBitX

 

An automatic tuner protects the rig during TX.  If the SWR is bad during TX, some of the signal coming out of the transmitter is reflected by the antenna back into the radio where it can cause damage.

That said, RX is optimized by a properly tuned antenna, but some good amount of signal still makes into the radio when receiving, even when the antenna is not perfect.

So I assume Doc G² is scanning for radio traffic, and then when he finds some if he wants to transmit he does something about his SWR for that frequency.


Re: No TX #ubitx

joe kallo <quietglow@...>
 

Me too! I even turned up the bias pots a little. Didn't help. I also removed the radio from the box and set it up again with jumpers, also with no effect.

Raj I am not sure exactly what you mean re: putting the wire to c80. I see c80, but I am not sure what you're suggesting I try to do.

Joe

Re: No TX #ubitx

Gordon Gibby <ggibby@...>
 

​I thought he was trying to create a tiny "antenna" to allow you to listen with another receiver and ascertain which STAGES were ampplifying.....




From: BITX20@groups.io <BITX20@groups.io> on behalf of joe kallo <quietglow@...>
Sent: Tuesday, January 2, 2018 6:53 PM
To: BITX20@groups.io
Subject: Re: [BITX20] No TX #ubitx
 
Me too! I even turned up the bias pots a little. Didn't help. I also removed the radio from the box and set it up again with jumpers, also with no effect.

Raj I am not sure exactly what you mean re: putting the wire to c80. I see c80, but I am not sure what you're suggesting I try to do.

Joe

Re: #ubitx Power output on 40 / 80 m with high current levels #ubitx

John Backo
 

Good job, Alex:

The more you explain, the more it looks like there is VHF oscillation
occurring at the lower frequencies. Jerry's suggestion of adding 10
ohm resistors to the gates is designed to suppress oscillation. It seems
to be the standard "repair" and almost always works...

The observation of greater gain in the output chain of the uBITX with
lower frequencies is also interesting. That would probably help to explain
some of the overdrive you are experiencing. The fact that Farhan did
not report it means that he either did not measure it or he did not drive his
rig to the point where it became a problem. If you examine the W7ZOI paper,
you will see that gain on the amplifier is adjustable with the proper choice
of bias and feedback resistors. That may have to be done.

I suspect, though, that your real problem is oscillation with transmit in the
lower bands. There have been various methods derived to attack the problem.
Yours is as good as any (maybe). Hi. The finding that power output decreases
the higher one goes in frequency is perfectly consistent with these devices.
That's a good sign that the basic design and operation is right...and that the
layout for higher frequencies is good. The real problem seems to be oscillation and
the overdrive from RV1 at lower frequencies. This is probably what is to be expected
as the gain of the IRFxxx MOSFETS increases rather dramatically below 40m.
Perhaps it might be simpler to provide a simple attenuator inline for driving these ranges.
It would seem that your layout is too much for the lower bands and requires more
gain suppression.

Keep it up. You're doing good...Farhan?

john
AD5YE

Re: #ubitx Power output on 40 / 80 m with high current levels #ubitx

John Backo
 

Incidentally, it would be nice to see exactly how your particular layout
differs from that of hfsigs. Can you upload a picture or two?
And I presume it is more through-the-hole and not smd parts. No?
It may be that the choice of parts is more critical than first believed.

john
AD5YE

Re: uBitx IRF510 to IRF510 physical measurement

Tom Christian
 

Bill, Thanks for the good idea (and John for your input too).  I ordered the heatsink as opposed to my original idea of mounting to the metal case (isolated).  Still waiting for the ubitx and the heatsink.  I would be curious to know how it goes for you.
Tom
AB7WT

Re: BCI filter question.

K9HZ <bill@...>
 

You can build an excellent W3NQN BC filter for about $5. 


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ

 

Owner - Operator

Big Signal Ranch – K9ZC

Staunton, Illinois

 

Owner – Operator

Villa Grand Piton - J68HZ

Soufriere, St. Lucia W.I.

Rent it: www.VillaGrandPiton.com


email:  bill@...

 


On Jan 2, 2018, at 7:52 AM, KG5NII <kg5nii@...> wrote:

I am thinking seriously about experimenting with the uBitX but am wondering in advance if someone could suggest  a good broadcast band filter I can build that is known to be effective. I live less than 1 mile (1.6 km) from a 50 kW AM broadcast station transmitting on 1180 kHz. I know this will be a problem with on the uBitX as even on mid, high end commercial ham rigs I get significant interference on 3540, 7040, 14160 kHz and so on.   In fact, I'd probably want to build an additional one for my Yaesu.  I know there are a lot of circuits out there for BCI filters but that doesn't necessarily mean they are or would be effective.  Cost is a major concern,  and commercial filter units seem to be rather pricey, but on the other hand, purchasing the components, etc may not necessarily be cost effective either given the somewhat high cost of shipping and given that  not everything could necessarily be purchased from one place, thereby rising costs even more.    I'd probably want to build one for the uBitX and one for my 100W Yaesu  just to give it over and done with.  There is not a day that goes by that I do not wish the four AM 1180 transmitter  towers down the road from me  are flattened by a tornado until I realize that would only be a temporary reprieve at best  but building, installing some good filters will be a permanent one.  


So advice please.


Thanks.

Ron, KG5NII



Re: My µBITX in its new home

Sajid Rahum
 

Ordered same box as well. Thanks for great feedback.
what did you do for the speaker?

Re: Si5351/A Utility Console

Bruce MacKinnon KC1FSZ
 

Hi:

I had a sweep feature on a different branch that I've merged in for general use.  Documentation is updated as well.  Basically, it's a simple way to sweep any of the clocks through a range, reading an analog pin at each step.  I've used this feature in several testing scenarios, particularly when trying to characterize a crystal band-pass filter or LC low-pass filter.  

There's also a trigger output at the start of each sweep that could be used to hook up an oscilloscope to get one of those old-school phosphor traces of your device.  Dim the lights, so cool looking ... 

The N2CQR blog included a write-up that I did when the feature was first created.  This gives you an idea of how it might be used:

http://soldersmoke.blogspot.com/2017/05/homebrew-peppermint-bitx-kc1fsz-goes.html

The digital read at each step in the sweep would be a power level or something useful like that.  Poor-man's Sweeperino I guess. But these methods yielded a fully working receiver, and I'm certainly no RF expert.

73s,

Bruce KC1FSZ

Re: Variable power control

Jack, W8TEE
 

Much of the rig power during receive is going to the Nano and display and si5351.  
Could cut that significantly with a 12 to 3.3v buck switcher (using 3.3v display and processor)
if you could get it clean enough.
Thanks, Jerry. This is one reason why I'm interested, as I'm moving to a Teensy 3.5, Si5351, and a true touch screen display.

Jack, W8TEE


From: Jerry Gaffke via Groups.Io <jgaffke@...>
To: BITX20@groups.io
Sent: Tuesday, January 2, 2018 5:03 PM
Subject: Re: [BITX20] Variable power control

Yes, a switcher is much more efficient than a linear regulator,
but amps of current getting switched at one mhz or so can create hash you hear in the receiver if 
not properly filtered and shielded.   I can receive well using a desktop 12v brick meant for use with a monitor, 
it is also a switching power supply, so it may be possible to use that ebay buck converter.

Another possibility is to normally power from 12dc, and enable a boost converter to generate 24v
only when transitting. Many switcher chips have an enable pin, though I don't see an enable 
talked about on most of the board level products available on the web.

Much of the rig power during receive is going to the Nano and display and si5351.  
Could cut that significantly with a 12 to 3.3v buck switcher (using 3.3v display and processor)
if you could get it clean enough.

Jerry, KE7ER

On Tue, Jan 2, 2018 at 01:47 pm, Jack Purdum wrote:
Why can I have a 24V supply and use this:    ebay # 152837387238
to drop the voltage to 5V? It seems that less power goes up in heat using one of these, so why won't these work?


Re: No TX #ubitx

 

That is fine Joe. Every board will not behave the same or even meters read the same.
Check why there is no RF getting to the finals.

At 02-01-2018, you wrote:
Right, so the directions say to go to min and then turn one pot until the current is 100mA higher, then to do the same w the other. Thats what I did, but my starting min current was 50mA lower than the spec in the directions. I didn't think it was enough it make a difference, but now with it not working I'm wondering.

To be clear, once I adjusted the bias as per the instructions, I measured 620mA when PTT was depressed.

Joe

Re: Tell me your favorite uBitx mods

Jack, W8TEE
 

I'm adding this to my development µBITX:

Inline image
Check on ebay #172488451918
Jack, W8TEE


From: David Arthur <mumrah@...>
To: BITX20@groups.io
Sent: Tuesday, January 2, 2018 5:03 PM
Subject: Re: [BITX20] Tell me your favorite uBitx mods

A mini usb "breakout" would be nice for uploading new Raduino sketches without opening up the box. Could double as a CAT control interface.

On Tue, Jan 2, 2018 at 4:53 PM K9HZ <bill@...> wrote:
I use the RD15HVF1 exclusively so i don't need to worry about multiple parts.  The gain of both parts is very close and they are pin compatible. 


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
 
Owner - Operator
Big Signal Ranch – K9ZC
Staunton, Illinois
 
Owner – Operator
Villa Grand Piton - J68HZ
Soufriere, St. Lucia W.I.

email:  bill@...
 

On Jan 2, 2018, at 11:09 AM, K5ESS <k5ess.nothdurft@...> wrote:

I would think they are a reliable source also.  Unfortunately they are no-stock on the RD16HHF1.  RD15HVF1-101 may work.  Anyone care to comment?
Mike
K5ESS
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Diver Martin
Sent: Tuesday, January 2, 2018 9:45 AM
To: BITX20@groups.io
Subject: Re: [BITX20] Tell me your favorite uBitx mods
 
My assumption is RFParts is a reliable source.  That's where I've gotten mine.  Given my employment with a semiconductor company that makes (competing) RF parts, I rarely go near ebay.
 
On Tue, Jan 2, 2018 at 7:43 AM, K5ESS <k5ess.nothdurft@...> wrote:
Yes.  This part is particularly prone to fakes.  It would be helpful if folks could post both reliable and unreliable sources for these.
Mike
K5ESS
 
From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jerry Gaffke via Groups.Io
Sent: Monday, January 1, 2018 11:23 PM
To: BITX20@groups.io
Subject: Re: [BITX20] Tell me your favorite uBitx mods
 
Careful with those $0.85 RD16HHF-1's
Often some random switcher FET with fresh paint.
Google "fake RD16HHF"

On Mon, Jan 1, 2018 at 08:03 pm, Dave Bottom wrote:
Maybe a shift to Mitsubishi RD16HHF-1 MOSFET is worth a try. ...  They are everywhere from $5 each here in the US to US $0.85 (China) in lots of 10.


 
--
Martin Held - AE7EU
http://ae7eu.com/
-------------------------------------------------------------------------------
If there aren't any questions, then what is there to learn?

--
David K4DBZ
Unofficial bitx chatroom: https://discord.gg/CrHvWFc


Re: Variable power control

Jack, W8TEE
 

Maybe Jerry's idea of only boosting on TX would be the way to go in removing any hash.

Jack, W8TEE



From: M Garza <mgarza896@...>
To: BITX20@groups.io
Sent: Tuesday, January 2, 2018 4:56 PM
Subject: Re: [BITX20] Variable power control

Jack,
Nothing wrong with that.  It should work fine, as long as it doesn't introduce any RF hash from the switching regulator.  
I would think that you could replace the variable that controls the voltage with a panel mounted one.

Marco - KG5PRT

On Tue, Jan 2, 2018 at 3:47 PM, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Ok, I'll probably look silly asking this, but you all know I'm a software guy, not EE, so here goes. Why can I have a 24V supply and use this:

ebay # 152837387238

to drop the voltage to 5V? It seems that less power goes up in heat using one of these, so why won't these work?

Jack, W8TEE



From: M Garza <mgarza896@...>
To: BITX20@groups.io
Sent: Tuesday, January 2, 2018 4:32 PM
Subject: Re: [BITX20] Variable power control

Kind of crude, but you could power the entire radio with 24v.  Use a 12v regulator for the receiver and a LM350 for a variable regulator to the PA.  You could set it up to be variable for only a few volts change to vary the output.  You alternately could use a 12 v source and the LM350 to vary the voltage to the PA.  Again, you could design something that would vary by a few watts.
Running from 24v lets you get the higher output but allows you to turn things down, as needed.

Here are a couple of  LM317/350/358 calculator pages:


Hope this helps.

Marco - KG5PRT



On Tue, Jan 2, 2018 at 3:20 PM, N8DAH <Dherron@...> wrote:
On Tue, Jan 2, 2018 at 01:17 pm, N8DAH wrote:
Group has a lot got smart folks I'm sure we will figure out a nice mod.
I am not one of them if you can tell by typing skills hihi






Re: No TX #ubitx

 

Joe,

The bias current flow is not linear with bias pot. The current will suddenly increase. Put your PS on current limit to about 1A
and then set the current.

touch or temporarily solder a short wire to the component so that it will act as an antenna. Then you can pick up your
low level TX signal on another receiver.

Raj

At 03-01-2018, you wrote:
Me too! I even turned up the bias pots a little. Didn't help. I also removed the radio from the box and set it up again with jumpers, also with no effect.

Raj I am not sure exactly what you mean re: putting the wire to c80. I see c80, but I am not sure what you're suggesting I try to do.

Joe

Re: Variable power control

John Backo
 

"I understand now that it's not a simple add of a potentiometer. Anyone done this yet?"

Jim, this is relatively simple for the BITX if one builds a linear power supply, and regulates
it with a LM338 or other regulator capable of 5A output. make the regulator variable by adjusting the
voltage input to the ground reference. Use about 24v for the top value and about 9v for the bottom.
Just be aware that the lower one goes in regulated voltage, the less current is available. But 12v and above
with 4-5A is easily possible. You can double these regulators with the proper configuration and so
double the output. Or you can easily add a bypass transistor and increase the power available that
way. See the datasheets for the details.


I use a similar home-brew power supply for all my bench work. It works well.

john
AD5YE

Re: No TX #ubitx

Ashhar Farhan
 

can you hook an RF probe together?

- f

On Wed, Jan 3, 2018 at 9:16 AM, Raj vu2zap <rajendrakumargg@...> wrote:
Joe,

The bias current flow is not linear with bias pot. The current will suddenly increase. Put your PS on current limit to about 1A
and then set the current.

touch or temporarily solder a short wire to the component so that it will act as an antenna. Then you can pick up your
low level TX signal on another receiver.

Raj

At 03-01-2018, you wrote:
>Me too! I even turned up the bias pots a little. Didn't help. I also removed the radio from the box and set it up again with jumpers, also with no effect.
>
>Raj I am not sure exactly what you mean re: putting the wire to c80. I see c80, but I am not sure what you're suggesting I try to do.
>
>Joe