Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
AAT (Automatic Attenuator Control)? _._
Hi Loris,
There are a lot of newbies here and they just don't know. Don't be
angry. Just help them alomng if they are actually open to help. I
started learning about physics and electronics in the early 1950s and I
still don't everything. I am more and moire aware of how much I don't
know. I usually do know where to look:)
73,
Bill KU8H
bark less - wag more
On 11/18/20 7:17 AM, IW4AJR Loris wrote:
> Hi Bill ... I fully agree with you!
> What I am wondering is "why" this forum continues to call AGC a very
> vulgar "ATTENUATOR" even if more or less automatic.
> 73 Loris
>
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WARNING: Promotional material
All:
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the bad news is that, evidently, I crossed some "printing threshold" as there was a significant
increase in the cost of producing the book. The good news is that the price remains
unchanged. If there are any questions, please use my SoftwareControlledHamRadio site to avoid using more bandwidth here.
Also, to those who wrote a review even with the crappy font...Thank you!
Jack, W8TEE
-- Jack, W8TEE
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Re: Interesting QST article
Simon
? Full circle. This all started with people modifying a QCX. It's great to see Hans supporting the hardware mod. Although, as he carefully notes, you will need firmware and support from the group.
You can also buy uSDX boards and parts from .
--
? 73
??? Bob? KD8CGH
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Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
Hi Curt and hi Gary ...
to be honest I'm not even a little angry, on the contrary I'm stimulated to try to learn something more (as Bill rightly says, the more I study the more I realize that I still need to learn something else!).
I agree with Curt for the excellent judgment he gives to the ?BITX, I own Version 6, but I believe that the judgment is applicable to all versions, especially I agree on the BF limiter that uses an LED and a photoresistor, it reminds me of a very old dynamic compressor circuit that I used 40/50 years ago on my HiFi to compress the dynamics of the Vinyl being recorded on magnetic tape.
I'm going crazy looking for the scheme among the old paperwork, there was a beautiful hardware solution that used an LED and a photostransistor (replaceable with a more convenient and less expensive photoresistor) stuck in a black plastic tube, if I find it again I scan it and I publish it, I will certainly remove the attenuator from the ?BITX and insert this solution !!!
For Gary, I conducted my experiments in 40m (band on which I love to do portable QSO) and the data collected refer to old HP and TEK instruments and perhaps they are a bit too penalizing, I used an HP8454B generator with HP11710B downconverter , an HP436A Bolometer with HP8481D head, a TEK2535 oscilloscope and a TEK2465B oscilloscope ... obviously, since the bolometer head is characterized only starting from 10MHz, it may be that it gave a slightly worse result than the real one, but not by a lot (half a point S counts for little against 2 or 3 points S) ... and to conclude I would say that to not blow the eardrums Curt's solution is definitely better than any other.
Finally, I feel like finding a way to realize a real good AGC to be inserted in the ?BITX, for example with an input amplifier MOSFET (perhaps with variable gain) driven by an AGC signal taken from the MF immediately after the quartz filter, I'm studying on ... if they are roses they will bloom.
a dear greeting ... IW4AJR Loris
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Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
Ok agree its not an agc. But it addresses the problem of having? your eardrums blown out with a sudden strong signal when you are wearing headphones. Plus it is easy to bypass. Just place a tiny reed relay across the board with nc contacts bridging the entire circuit. Relay off no "agc" relay on AGC Does anyone have an easy way to implement an actual AGC ?? One that can be managed by old eyes and old hands?
Hi Loris,
There are a lot of newbies here and they just don't know. Don't be
angry. Just help them alomng if they are actually open to help. I
started learning about physics and electronics in the early 1950s and I
still don't everything. I am more and moire aware of how much I don't
know. I usually do know where to look:)
73,
Bill KU8H
bark less - wag more
On 11/18/20 7:17 AM, IW4AJR Loris wrote:
> Hi Bill ... I fully agree with you!
> What I am wondering is "why" this forum continues to call AGC a very
> vulgar "ATTENUATOR" even if more or less automatic.
> 73 Loris
>
|
Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
Loris
Interesting viewpoint, as I agree it is unusual to place AGC attenuation at the very front. I had not seen any loss measurements, and I imagine they vary with frequency. Perhaps they are not as high as you cite at HF.
The designer had a good motivation seeking to enhance dynamic range, but the ubitx already seems to have its gain conservatively distributed. My antennas are mere dipole, verticals and 2 element compact yagi. The ubitx is not swamped even with many big amateur stations here in Maryland.
On low HF atmospheric and man made noise dominate more than receiver noise figure, but up on 28 MHz this added loss, whatever it is, will have impact in not hearing as well.
As the designer, who left out agc to keep ubitx simple and affordable around the globe, suggests an IF agc such as w7zoi hybrid cascode would be ideal (I have one here not in use yet). In the ubitx design it can be integrated but with directional amplifiers that do TR switching it may not easily patch in.
Rigs do work without agc, it just means operator must regularly use the audio gain control knob. I find only that loud signals are uncomfortable when tuning across the band. The simple, novel circuit using an LED and photoresistor does this wonderfully.
Curt
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Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
Hi Loris,
There are a lot of newbies here and they just don't know. Don't be angry. Just help them alomng if they are actually open to help. I started learning about physics and electronics in the early 1950s and I still don't everything. I am more and moire aware of how much I don't know. I usually do know where to look:)
73,
Bill KU8H
bark less - wag more
toggle quoted message
Show quoted text
On 11/18/20 7:17 AM, IW4AJR Loris wrote: Hi Bill ... I fully agree with you!
What I am wondering is "why" this forum continues to call AGC a very vulgar "ATTENUATOR" even if more or less automatic.
73 Loris
|
Re: #For Sale A Few QRP Goodies
#for
Mestre David - N8DAH
Meus parabens, ¨¦ um sonho!!!? Por que voc¨º quer vender tudo isto? PY2PVB Rubens Kamimura
GG49in07 Em ter., 17 de nov. de 2020 ¨¤s 02:27, N8DAH < Dherron@...> escreveu:
I have for sale a few kits from my radio desk that just don't get used.
50w QRP-Labs Amp 40m:
Built and tested by me with added 24v fan. I will also include a hand PTT that plug's into the amp and hit the red button when you are ready to TX (9v not included). PTT on this amp is high 5v and was meant to be used with the QCX line of radios. I made the hand key to use with other radios and testing, it's a 5v regulator and a push button wired to the 9v battery.
Asking 75$ Shipped CONUS or 90$ Shipped EU/UK or 85$ shipped CA
Antuino Black Box Testing Unit:
Bought from HFsignals at 2019 FDIM. This has been calibrated and updated with the new hardware mods and latest firmware. Tested and working! Box paint keeps chipping off real easy, see pictures.
Asking 80$ Shipped CONUS or 95$ EU/UK or 90$ CA
Phaser 40m:
SER#80
Built and tested by me run's solid FT8/JS8 with enclosure, calibrated getting about 3-4Watts out.
105$ Shipped CONUS or 120$ EU/UK or 115$ CA
Take the lot for: 250$ Shipped CONUS or 265$ EU/UK or 260$ CA
Paypal preferred I pay fee's, ALL friends and family payments will be rejected.
Thanks for looking.
73
--
David
?N8DAH
       
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Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
Hi Bill ... I fully agree with you!
What I am wondering is "why" this forum continues to call AGC a very vulgar "ATTENUATOR" even if more or less automatic.
73 Loris
|
Re: Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
Hi,
Attenuating the signal at the receive antenna input is not gain control at all. Attenuation can reduce overwhelming signals that distort the receiver front end and make those very weak signals copyable again. It may seem counterintuituve to improve weak signal reception by increasing attenuation at the antenna but that is *exactly* what happens.
Automatic Gain Control may be applied to an RF amplifier immediately following the antenna input and before the first mixer but that is not attenuation. Some os us still like to have manual gain control applied in the RF and IF sections. A manual attenuator that can be switched out completely is an excellent choice and one that I prefer. Not a PIN diode.
73,
Bill KU8H
bark less - wag more
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On 11/18/20 5:11 AM, IW4AJR Loris wrote: From my tests and from the measurements made, it appears to me that the best known "AGC" modification module is a very bad "ATTENUATOR" placed in series with the receiving antenna!
Although I have tried, measured and studied the scheme and compared it with the reality installed on my ?BITX-V6, the theory of the principle used confirms what the practice shows:
Although an automatic attenuator placed in series with the antenna is excellent (try it yourself with the best PIN attenuators on the market) the residual attenuation of the circuit at the minimum attenuation will never be less than -3dB, often, even in the most refined circuits. , yes it gets a minimum of -5 / -6 dB! ... not to mention what two poor quality MOSFETs can do (compared to a PIN diode attenuator) ... the best measurement I got was -10 / -15 dB, which is equivalent to losing at least 2 S points on the reception!
It is totally unacceptable! and technically from "geeks" and not from radio amateurs!
From my tests, only one module acts correctly on the "gain" of the MF amplification and, even if a bit obsolete and bulky (it is not built in SMD), it would seem the most efficient module, not changing the "sensitivity" of the receiver (very important thing in DX also in QRP).
Why do you insist on referring to these "ATTENUATORS" as "AGC" "Automatic GAIN Control"?
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Re: K5BCQ board layout and pinouts
It is not an AGC it is an antenna attenuator and good if you go to you will lose from 2 to 3 points S in reception, the system is not bypassable, even when turned off the MOSFET remains inserted in series with the antenna and, as in all "attenuators "automatic (look at some articles on PIN diodes), there is a residual attenuation that cannot be eliminated ... if you don't mind losing S points from your receiver, use it, but don't call it" AGC "it is doesn't and it doesn't check any "gain", simply "attenuates the antenna input signal".
73 Loris
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Re: Interesting QST article
The new QCX mini in the pipeline from QRPLabs is proposed to come with some simple circuit modifications built in to make it easy to turn the QCX mini into a ucx (there are some user supplied parts required).
A much simpler way to try this circuit than the "from scratch" approach if that is preferred.?
73
Simon
VK3ELH?
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Re: Interesting QST article
The uSDX is a development effort that has several evolving designs, it's not a single product like the uBITX V6. One cool aspect of it is that it uses a highly efficient class E amp not only for CW, but for other modes too. It pulls off this wizardry by pulse width modulating the power to the amp. It's a uses direct conversion SDR receiver with the rest of the signal processing done computationally. The amazing thing is that all of this, including A/D and D/A, is all done by an Arduino so there is a very low discrete parts count.
It started single band as a modification of QRP Labs QCX class E amp CW transceiver. The two main design streams now have multiband filter boards.?
Check out the uSDX group.io WIKI for an overview.
I built a uBITX V4, a WB2CBA uSDX and I'm slowly building a DL2MAN version uSDX (I'm not so good with SMD). In my opinion, compared to the uBITX, the uSDX has more features like AGC and variable filters. It's better at CW since it's QSK and has filters you can narrow, but the SSB transmission is not as good. The uSDX firmware is evolving rapidly, like in the early uBITX days,? so we'll see how it progresses.
BTW Farahan often participates in uSDX discussions. I wouldn't be surprised to see a new transceiver from HF Signals.
--
? 73
??? Bob? KD8CGH
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Question: Why do you call "AGC" a simple automatic antenna "attenuator" in this forum?
#ubitx
#ubitxv6
From my tests and from the measurements made, it appears to me that the best known "AGC" modification module is a very bad "ATTENUATOR" placed in series with the receiving antenna!
Although I have tried, measured and studied the scheme and compared it with the reality installed on my ?BITX-V6, the theory of the principle used confirms what the practice shows:
Although an automatic attenuator placed in series with the antenna is excellent (try it yourself with the best PIN attenuators on the market) the residual attenuation of the circuit at the minimum attenuation will never be less than -3dB, often, even in the most refined circuits. , yes it gets a minimum of -5 / -6 dB! ... not to mention what two poor quality MOSFETs can do (compared to a PIN diode attenuator) ... the best measurement I got was -10 / -15 dB, which is equivalent to losing at least 2 S points on the reception!
It is totally unacceptable! and technically from "geeks" and not from radio amateurs!
From my tests, only one module acts correctly on the "gain" of the MF amplification and, even if a bit obsolete and bulky (it is not built in SMD), it would seem the most efficient module, not changing the "sensitivity" of the receiver (very important thing in DX also in QRP).
Why do you insist on referring to these "ATTENUATORS" as "AGC" "Automatic GAIN Control"?
|
Re: K5BCQ board layout and pinouts
Arv, the speaker detached and bounced around. ?Finals were bent and the AGC board was ripped out of the three pin connector. ?Hot on the trail, I bent the transistors back straight, did some soldering and labeling and ... just now... found the initial instructions for the AGC board so I am all set. ?For the others... ? ?here is the link I found. ???
The transmitter is now fully functional and this will help me to fix the AGC board. ?(was thinking of jumping the pc board but think I will just complete the wiring.) ?
I got a great deal on this uBitz and looking forward to getting it on the air (with the AGC board!)
--
Frank, KG9H
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Re: K5BCQ board layout and pinouts
Frank, KG9H
What are the symptoms (what works and what does not work)?
A picture of the damaged board might be interesting. Pinout for the off-board connections are in the assembly manual. Pinout for the on-board units (Radiuno, etc.) are in the assembly manual.
A picture of the as-received shipping material would be helpful for future reference.
Arv _._
I purchased a uBitz (4 I think) and it has a?K5BCQ board in it.? It bounced around during shipment and the board came apart.? I think I can get it running.
Just need the pin-out information, anyone?
--
Frank, KG9H
kg9hfrank@...
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K5BCQ board layout and pinouts
I purchased a uBitz (4 I think) and it has a?K5BCQ board in it. ?It bounced around during shipment and the board came apart. ?I think I can get it running.
Just need the pin-out information, anyone?
--
Frank, KG9H
kg9hfrank@...
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Re: #For Sale A Few QRP Goodies
#for
Amp has been sold -- David
?N8DAH
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Re: Interesting QST article
Hi,
It has been done over and over again from the time of earliest vacuum tube gear right up to recent days. It is a viable concept. See how you can use plug-in band changes on the newest gear:)
73,
Bill KU8H
bark less - wag more
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On 11/17/20 6:41 PM, Tom, wb6b wrote: On Tue, Nov 17, 2020 at 02:49 PM, Shirley Dulcey KE1L wrote:
That allows it to be moved to another band by replacing the board
with one for another band.
At some point I wonder if it would be possible to build QRP to moderate power TX stages at low enough cost, that rather than using relays or other filter switching methods for a multi band transceiver, you could just have a separate final RF power transistor and filter for each band. Just turn on the output section for the band you are interested in. Hopefully the filter sections could be designed so they could just be common connected together for the antenna connection.
Tom, wb6b
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Re: Interesting QST article
On Tue, Nov 17, 2020 at 02:49 PM, Shirley Dulcey KE1L wrote:
That allows it to be moved to another band by replacing the board with one for another band.
At some point I wonder if it would be possible to build QRP to moderate power TX stages at low enough cost, that rather than using relays or other filter switching methods for a multi band transceiver, you could just have a separate final RF power transistor and filter for each band. Just turn on the output section for the band you are interested in. Hopefully the filter sections could be designed so they could just be common connected together for the antenna connection.? Tom, wb6b
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Bob Benedict, KD8CGH
N8DAH