Author: ecDate: 04:19 24-11-06
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Hi
I want to build an AM radio receiver by myself.
My question is: what is the right amplification that the first RF amp stage
should have ?
Is there any rule ?
Thanks
ec
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Author: Tom BiasiDate: 05:41 24-11-06
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"ec" <wavesoft@netvision.net.il> wrote in message
news:ek6de7$m2l$1@news2.netvision.net.il...
> Hi
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp
> stage should have ?
>
> Is there any rule ?
>
> Thanks
> ec
>
It depends on what you will need for your next stage.
May I suggest that you build a kit. The instructions will describe the
function of each stage as you build it.
I used Ramsey kits in my classes for years and they were decent as
educational projects.
Regards,
Tom
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Author: RadiosrfunDate: 08:27 24-11-06
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"Tom Biasi" <tombiasi@********optonline.net> wrote in message
news:M%z9h.509$ZM.203@newsfe11.lga...
>
> "ec" <wavesoft@netvision.net.il> wrote in message
> news:ek6de7$m2l$1@news2.netvision.net.il...
>> Hi
>> I want to build an AM radio receiver by myself.
>>
>> My question is: what is the right amplification that the first RF amp
>> stage should have ?
>>
>> Is there any rule ?
>>
>> Thanks
>> ec
>>
>
> It depends on what you will need for your next stage.
> May I suggest that you build a kit. The instructions will describe the
> function of each stage as you build it.
> I used Ramsey kits in my classes for years and they were decent as
> educational projects.
>
> Regards,
> Tom
>
There used to be a company I "believe" named "Graymark" which made
"educational" Electronics kits. Our school shop class used them. They were
decent for "learning". "I'm" not sure about their "radio"
but the "Power
Supply" with alligator clip leads was cool. It was small but basically
replaced batteries (then) as a sort of over sized Walwart.
It sure is nice to see some interest in this area. If you have problems
finding said kit, use "any" - to keep the spark alive. Homebrew (make from
scratch) if you want.
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Author: Michael BlackDate: 10:58 24-11-06
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"ec" (wavesoft@netvision.net.il) writes:
> Hi
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp stage
> should have ?
>
> Is there any rule ?
>
But the question can't be answered without any indication of your needs, or
what the rest of the receiver is.
Most AM broadcast band radios are sensitive enough, and have no RF stage.
An RF stage often has other reasons than gain. If you want better filtering
at the front of the receiver, to keep down images for instance, you might
want an amplifier stage there to compensate for the losses in the tuned
circuits.
Gain later in the receiver has the advantage that it's on a fixed frequency,
which is the point of superheterodyne receivers; convert the incoming signal
to a fixed frequency where selectivity and amplification can be had without
the problems that come with making it tuneable. Put the gain at the fixed
intermediate frequency, and you won't have to worry about making the stage
tuneable (and maybe more important from the standpoint of construction, you
won't have to get it to tune with the rest of the tuneable stages).
So you wouldn't put gain at the front of the receiver unless there was
a very good reason.
Michael
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Author: Homer J SimpsonDate: 12:53 24-11-06
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"ec" <wavesoft@netvision.net.il> wrote in message
news:ek6de7$m2l$1@news2.netvision.net.il...
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp
> stage should have ?
>
> Is there any rule ?
You'd do well to go get an ARRL handbook (most libraries) and study that.
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Author: Andrew HolmeDate: 17:58 24-11-06
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"ec" <wavesoft@netvision.net.il> wrote in message
news:ek6de7$m2l$1@news2.netvision.net.il...
> Hi
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp
> stage should have ?
>
> Is there any rule ?
>
> Thanks
> ec
To maximise dynamic-range, the RF amplifier stages of high-performance HF
communications receivers typically have just enough gain to compensate for
the insertion loss of the first mixer.
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Author: matt7375@gmail.comDate: 21:55 24-11-06
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ec wrote:
> Hi
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp stage
> should have ?
>
> Is there any rule ?
>
> Thanks
> sssec
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Author: Bill BowdenDate: 21:58 24-11-06
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ec wrote:
> Hi
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp stage
> should have ?
>
> Is there any rule ?
>
> Thanks
> ec
If you want to build a superhet receiver with a tuned RF stage, you
will need a variable capacitor with 3 sections to tune the antenna,
oscillator and RF stage. Most AM radios use a tuning capacitor with
only 2 sections to tune the oscillator and antenna without a RF stage.
But it's difficult to design your own AM radio, since you need about
90dB of gain in the IF stages, and that isn't easy to do without the
whole thing oscillating at 455kHz. I've tried it, and never could get
the thing to start amplyfing and stop oscillating.
Anybody know of an easy way to get 90dB gain at 455kHz without the
thing oscillating?
-Bill
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Author: RobinDate: 05:27 27-11-06
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ec wrote:
> Hi
> I want to build an AM radio receiver by myself.
>
> My question is: what is the right amplification that the first RF amp stage
> should have ?
>
> Is there any rule ?
>
> Thanks
> ec
Did you know that you might not need it? At least for your first try.
If you dangle a piece of wire out the window ( or possibly across the
floor ) as an aerial you can get more than half a volt of RF out of it
i.e. measured between one end and e.g. a radiator pipe.
This is enough to power a "crystal set" directly i.e. a handful of
components including a crystal ear piece (or even headphones if you can
get ancient "war time" variety of e.g. 2000 Ohms impeadance - normal
headphones won't work, finding out why will be a big moment for you).
Cheers
Robin
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Author: Rich GriseDate: 20:38 28-11-06
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On Fri, 24 Nov 2006 18:58:55 -0800, Bill Bowden wrote:
> ec wrote:
>> Hi
>> I want to build an AM radio receiver by myself.
>>
>> My question is: what is the right amplification that the first RF amp stage
>> should have ?
>>
>> Is there any rule ?
>
> If you want to build a superhet receiver with a tuned RF stage, you
> will need a variable capacitor with 3 sections to tune the antenna,
> oscillator and RF stage. Most AM radios use a tuning capacitor with
> only 2 sections to tune the oscillator and antenna without a RF stage.
>
> But it's difficult to design your own AM radio, since you need about
> 90dB of gain in the IF stages, and that isn't easy to do without the
> whole thing oscillating at 455kHz. I've tried it, and never could get
> the thing to start amplyfing and stop oscillating.
>
> Anybody know of an easy way to get 90dB gain at 455kHz without the
> thing oscillating?
Shielded transformers and neutralized IF amp stages. :-)
Cheers!
Rich
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Author: Michael BlackDate: 22:20 28-11-06
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Rich Grise (rich@example.net) writes:
> On Fri, 24 Nov 2006 18:58:55 -0800, Bill Bowden wrote:
>> ec wrote:
>>> Hi
>>> I want to build an AM radio receiver by myself.
>>>
>>> My question is: what is the right amplification that the first RF amp stage
>>> should have ?
>>>
>>> Is there any rule ?
>>
>> If you want to build a superhet receiver with a tuned RF stage, you
>> will need a variable capacitor with 3 sections to tune the antenna,
>> oscillator and RF stage. Most AM radios use a tuning capacitor with
>> only 2 sections to tune the oscillator and antenna without a RF stage.
>>
>> But it's difficult to design your own AM radio, since you need about
>> 90dB of gain in the IF stages, and that isn't easy to do without the
>> whole thing oscillating at 455kHz. I've tried it, and never could get
>> the thing to start amplyfing and stop oscillating.
>>
>> Anybody know of an easy way to get 90dB gain at 455kHz without the
>> thing oscillating?
>
>
> Shielded transformers and neutralized IF amp stages. :-)
>
Wasn't there an improvement when they brought in those newfangled
pentodes arrived on the scene? Did away with the fussiness of those
triodes.
(On the other hand, if pentodes had been invented before the triode,
would that have delayed the "discovery" of oscillation and regeneration?)
Michael
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