Has anyone tried a H11F3M for the AGC on the newer uBITX ??It's a Photo FET Optocoupler made by ON Semi and actually shows an application note with AGC use. You could drive it with the existing second amplifier, minimal extra components, and a 6-pin socket which will fit on the board near the amplifier. I would also put in an 8-pin socket on the TDA2822M/NJM2073D amplifier for future convenience.....might as well, while you are messing around with the board. Just received some to try out.

73 Kees K5BCQ

Jerry,

I've looked at the hycas setup before. The AGC detector isn't a lot
different than what Don has used. The only difference is the use of a
differential amplifier and a PNP AGC driver.

There are always delays associated with feedback loops. I remember
working on noise blankers back in the 80's. I was trying to duplicate
the old Henry Radio Tempo 2020 which had the best noise blanker I have
ever used. I finally figured out that they had actually engineered in a
delay circuit in the IF so that the noise detector situated prior to
the IF amp chain could actually blank the IF while the noise pulse was
passing through the IF chain. I never did figure out a way to duplicate
this in a simple manner.

Using audio to attenuate IF gain will always suffer from a delay. I
could actually see it in my 2008 receiver using a two-channel
oscilloscope There will always be a "blurp" of a strong signal that
gets passed along before the AGC can suppress it. If the delay is such
that a 180deg phase shift can happen then you have basically designed
an oscillator!

I suppose this could happen but I don't think this receiver is complex
enough to generate those kinds of delays.

I agree with you on the PIN diode. I probably should order a few to
play with. I want to get Don's circuit put in first so I will have a
baseline to compare it to.

tim ab0wr

On Wed, 28 Mar 2018 08:49:44 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

A google for "w7zoi hycas" will show a well regarded AGC system.
It gives nearly 60dB of gain when there's no AGC action, about 40 dB
more than the uBitx 12mhz IF has. Lots of parts, but most are under a
nickle. Could be a $10 board if autostuffed with surface mount parts.

Henning mentions possible trouble due to filter delays if the AGC
attenuator/gain-control is prior to the the IF filter?and the AGC
detector is after the the filter, something to be aware of:
/g/BITX20/message/32090 Don's audio detect + FET rf
attenuator is apparently not suffering any instability from this.

I have no idea what Bill is doing, but if he plans to have an AGC
detector before the 12mhz filter it will be interesting to see how he
goes about making that work.

I'm still thinking a PIN diode bridge in one of the IF amps as the
attenuator plus an audio based AGC detector. Simple enough, and the
uBitx doesn't need any more gain.

Jerry

What is the link to the assembly instructions you are using?

Leonard

--
----------
N5WLF, Greggory (or my nickname, Ghericoan)
General Class, Digital Radio Hobbyist

I use ethernet wire for breadboarding.

some of those headphones use litz wire....

For some reason I have not been getting any message from the group in my email.? I just checked my settings and all seems to be correct.? What happened???

You mentioned Winlink, so I assume you are using CAT control. Every time I've experienced this when using CAT, it was caused by RF getting into something. With my setup, whenever I run more than 2W on 30m I am ending up with TX not getting turned off. For other bands, the limits are a bit higher. I've added chokes to the USB cable from the computer to the serial adapter, and another one on?the cable from the serial adapter to?the radio, but so far this has not made any difference. I'll probably add a few more chokes on power supply and audio cables to see if I can fix this.?

You may want to try turning down TX power to see if that makes a difference.?
--
Karl Heinz - K5KHK

On Wed, Mar 28, 2018 at 10:19 am, Scott Docter wrote:

开云体育

Most of us in the forum have the rigs from hfsignals.com
Do you have one of these from Sunil?
? ??
Most of us have no idea what transmit current into the exciter should be on Sunil's board set.
I suspect Ashhar does not either.

Anyway, my guess would be that current increase when going to transmit on that exciter would mostly be around Q14.
I suggest you measure DC voltages at Q14's emitter, base and collector for transmit and receive.
Should be around zero for receive, well above ground for transmit.

Also, if you want to keep an intelligent conversation going on this, don't change the subject heading.
Took me a few minutes to find your old thread where the problem was described.

Jerry

################

?

I printed mine out on with an inkjet printer on regular photo paper and then put some clear tape over it to preserve it.
Dan, W2DLC

A google for "w7zoi hycas" will show a well regarded AGC system.
It gives nearly 60dB of gain when there's no AGC action, about 40 dB more than the uBitx 12mhz IF has.
Lots of parts, but most are under a nickle.
Could be a $10 board if autostuffed with surface mount parts.

Henning mentions possible trouble due to filter delays if the AGC attenuator/gain-control is prior
to the the IF filter?and the AGC detector is after the the filter, something to be aware of:
? ??/g/BITX20/message/32090?
Don's audio detect + FET rf attenuator is apparently not suffering any instability from this.

I have no idea what Bill is doing, but if he plans to have an AGC detector before the 12mhz filter
it will be interesting to see how he goes about making that work.

I'm still thinking a PIN diode bridge in one of the IF amps as the attenuator plus an audio based AGC detector.
Simple enough, and the uBitx doesn't need any more gain.

Jerry

I get most of my small diam wire by stripping it out of old TV sets or radios.

Plenty of good stuff if you take the time to look.

73
Jim N6OTQ

开云体育

I heard it called " it is a new Feature"!

Mike, WA6ISP

Sorry, OM. I didn't notice anything after installing this smd part. Still a pop when starting and finishing tx, but I'll get used to it.
As Microsoft states "Windows have no bugs, they're properties".

Kai, OH3WE

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

Oops! Forgot the attachment!

tim ab0wr

On Wed, 28 Mar 2018 10:08:24 -0500
"Tim Gorman" <tgorman2@...> wrote:

Jerry,

Been going back thru my old notes. Attached is a schematic of an agc
amp I used on a single conversion receiver I built back in 2008. It
even provides for an S-meter. The AGC was designed to work with an
MC1550 IF Amp IC but I don't see why it couldn't be used to drive a
2n7002 as well. Might have to change values to provide the right gate
voltage, I'll have to do some calculations.

tim ab0wr

On Tue, 27 Mar 2018 18:40:29 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

Detecting RF for AGC would have to happen after the 12mhz crystal
filter.

Not really… it can happen anywhere in the chain.? The issue is the
bandwidth of:
? 1) the attenuator and 2) the detector used for the AGC.?
? With the right parts, anything is possible.

AGC should detect what's in the passband of the receiver, nothing
more, nothing less. If RF into the AGC detector is wider, then any
QRO signal in the band will quiet the receiver. I can vaguely
imagine ways to make it work with the AGC detector in front of the
IF filter, but they aren't pretty.? ?I'm fine with just detecting
the audio on a $109 transceiver.

Let us know how your AGC scheme works once finished.
Though I'm more in Don's camp, agonizing about whether a $0.50 PIN
diode array is worth the expense when a $0.02 FET is almost good
enough.