EMRFD Message Archive 7751
Message Date From Subject 7751 2012-09-07 21:43:07 KK7B On the concept of absolute correctness... ...there is none of that anywhere in EMRFD. All of the circuits are experimental. The idea that a schematic in EMRFD is carved in stone is quite frightening. None of the authors treat circuits that way. The more useful a circuit, the more variations will exist.
7752 2012-09-07 23:26:43 Paul Anderson Re: On the concept of absolute correctness... And, frankly, if the circuit is treated as inviolable then it isn't exactly "experimenting" :)
7753 2012-09-08 05:25:11 Dean Blake Re: On the concept of absolute correctness... Amen! Circuits are creations. they can vary and they all will perform differently, even the layout sometimes affects them!
Date: Sat, 8 Sep 2012 04:43:04 +0000
Subject: [emrfd] On the concept of absolute correctness...
...there is none of that anywhere in EMRFD. All of the circuits are experimental. The idea that a schematic in EMRFD is carved in stone is quite frightening. None of the authors treat circuits that way. The more useful a circuit, the more variations will exist.
[Non-text portions of this message have been removed]
7754 2012-09-08 08:28:51 kb1gmx Re: On the concept of absolute correctness... Amen, It's a suggestion, hint and should be treated like that.
I prefer to talk in terms of topology. We had that here a while
back on regarding MOSFETS as wide band amplifiers with feedback.
It's the same topology as the bog standard 2n5109 wide band amp
with degenerative feedback on the emitter and collector to base resistive feedback. The fact that once you add bias and other
incidental parts needed to make a complete working stage is
what is the often confusing issue for many.
To that I add.. What EMRFD tries to do but, is very hard to do
well, is explain what parts in a circuit are important and what
others are there to make the circuit complete. The fact that
often parts do both muddies the water and confuses some.
However, the mantra was experiment and measure. That reveals all.
After many decades of engineering I still find "lets build it and
see" to be the most interesting and revealing aspect of electronics.
With that I plan to spend a few hours playing with a circuit
from the 1970 fifth editi
7757 2012-09-08 19:12:30 William Re: On the concept of absolute correctness... Allison,
"I have an old crystal filter from a Heathkit HW12 junker in
Me too. Actually several. I have junked a few HW rigs in the past and saved these 2.305khz four pole crystal filters, the L1 inductor and the 2.3067khz BFO crystal.
Question: What do you think the impedance is on this filter?
Looking at the old Heath schematic the input is driven from the plate of a 6EA8 IF tube through a 4700 ohm resistor/.02uf cap to ground. The output side goes to the grid of a 6AU6 with a grid resistor of 4700 ohms.
Safe to say the filter is about 5000 ohms?
I have several of these filters and they might make a good filter for a single band homebrew rig.
7758 2012-09-09 05:33:03 kb1gmx Re: On the concept of absolute correctness... Thats easy..
The HW12 schematic has 4700 ohm on the plate and the following grid has 4700 ohms so I"d say a fair bet the termination impedance is 4700 ohms or slightly less.
I have the same thoughts for use but I'm thinking a retro all
bipolar design. based on the December 1967 QST Transceive with
transistors (almost) design.
That makes it interesting to interface to transistors where
the base is usually 600 ohms and down and the collector is more likely determined by the load resistor and the dynamic load presented by the transistor. FETs of any type can do that.
In my case I just cut the complete filter secti
7759 2012-09-09 07:50:46 Ashhar Farhan Re: On the concept of absolute correctness... show me a perfect component, and i will show you an absolutely correct
circuit... and remember, we are all footnotes to maxwell's four ...
7762 2012-09-10 06:36:46 William Re: On the concept of absolute correctness... Allison,
I suspected as so. I will keep that in mind for a future project.
I hope you have not thrown out the HW12 chassis etc. They make excellent boxes for new projects. Once you remove the old board you have a 12 inch by 8 inch space for an aluminum cover sheet. That is how I did the KK7B ur2 receiver. I had lots of space to add other circuits too.
In next projects I am going to use double sided copper 12 x 8 boards instead. Then I will be able to construct boxes top and bottom by soldering boards together.
Take a look in the photo section for my "recycled HW12".
7767 2012-09-10 16:30:37 kb1gmx Re: On the concept of absolute correctness... 7773 2012-09-11 17:37:28 kb1gmx Re: On the concept of absolute correctness... I tried something..
The 2305khz filter I tried to match it and 4700 is about right.
The match was a parallel LC using a Ft50-61 with 38 turns of wire
and 60pf trimmer in parallel. Using 3turn link (for about 50 ohm interface) it matched fairly well to a 4500 ohm load. On the
filter It needed 4700 ohms resistive to get a decent 2.5Khz wide filter and looks ok down 30db using noise and the spectrum
analyser (8568B) sweeping at 20sec and 10hz detection bandwidth and MAX hold to get some averaging. I could go deeper down the skirts
but then I'd need an amp ahead of the '65B as I was down to the
noise floor. That makes a good filter with a predictable
7774 2012-09-12 21:11:16 William Re: On the concept of absolute correctness... >Allison,
> I think I have a filter for a simple 40M radio..
That sounds great. I will make a few notes and when the time comes run a few experiments myself.
Yes it would make a decent filter for a simple receiver. I have two complete sets with the L1 inductor and one set with just the crystals by themselves.
Thanks for the tip.