AM tuner?

[Robert Morein]

I have an interest in sampling AM talk shows over a wide geographic range.
At night, I can pick up many stations east of the Mississippi, and some all
the way to the Rockies.

AM reception is generally plagued with whistles, known as heterodynes, that
are intermodulation products from stations on adjacent frequencies. Some
communications receivers are equipped with notch filters and/or digital
processing to remove these.

Are there any tuners specifically for the AM "phile", that incorporate these
features. Wide bandwidth is not a must for my purpose, but heterodynes are
very fatiguing. I could purchase a modern communications receiver, but these
are expensive.

[[email protected]]

Probably not.

AM stations are at 10 kHz intervals in the US and therefore that's
where many of the notches are. A 10 kHz notch filter in the audio
domain can be built or a commercial parametric EQ will give good
service.

Filtering at the IF level involves use of LC, crystal, or mechanical
filters at the radio's IF frequency. These are still available but many
will be too narrow for satisfactory performance.

Purchasing a tube era communications receiver might be your best bet
because although quality National, Hammarlund or Collins receivers are
expensive, their continued value is pretty much assured until the
generation of hams who grew up lusting after them completely dies. They
are long lived,even being tubed, because they were very conservatively
designed.

Solid state receivers such as the popular ICOM series have fine RF
performance but have legendarily bad audio sections. You can come off
the factory 10.7 IF output and feed this into a commercial "back end"
such as the Sherwood SE-3 or a homebuilt detector and filter section.
There are solid state comm receivers with better audio but they are
high dollar.

Least expensive alternative may be a common car AM receiver. Put into
a box with a 12 volt power supply, an RF balun for longwire or 50 O
(wow...does the omega really work on Usenet??) antenna and a small
speaker that has poor response at 10 kHz, early solid state Delco AM
car radios offer superb RF specs for very little or no money.

[Robert Morein]

> wrote in message
oups.com...
> Probably not.
>
> AM stations are at 10 kHz intervals in the US and therefore that's
> where many of the notches are. A 10 kHz notch filter in the audio
> domain can be built or a commercial parametric EQ will give good
> service.
>
But it seems that many of the notches are not at 10 kHz. I onceexperimented
with a notch filter, and discovering that a single notch could not remove
all of them.

So there's no digital gadget that will clean it up in one swoop?

Now I'm thinking I have a couple of laboratory notch filters lying around.
That might be the solution.

[[email protected]]

DSP could with the right code, of course. Perhaps you should look at
the software-defined-radio stuff out there which includes some GNU
software. I believe boards (bare and stuffed) are available.

I think you'd do well just to buuild some analog notch filters and
tweak as needed. The old Cinema Engineering jobs could do the job but
they are big and heavy. For talk radio a commercial IF filter at 5 kHz
center bw might do nicely.

[Robert Morein]

> wrote in message
ps.com...
> DSP could with the right code, of course. Perhaps you should look at
> the software-defined-radio stuff out there which includes some GNU
> software. I believe boards (bare and stuffed) are available.
>
> I think you'd do well just to buuild some analog notch filters and
> tweak as needed. The old Cinema Engineering jobs could do the job but
> they are big and heavy. For talk radio a commercial IF filter at 5 kHz
> center bw might do nicely.
>
I have a bunch of Krohn-Hite filters.
The downside is it's a lot of rack space to listen to a talk show :)

[Trevor Wilson]

"Robert Morein" > wrote in message
...
>I have an interest in sampling AM talk shows over a wide geographic range.
> At night, I can pick up many stations east of the Mississippi, and some
> all
> the way to the Rockies.
>
> AM reception is generally plagued with whistles, known as heterodynes,
> that
> are intermodulation products from stations on adjacent frequencies. Some
> communications receivers are equipped with notch filters and/or digital
> processing to remove these.
>
> Are there any tuners specifically for the AM "phile", that incorporate
> these
> features. Wide bandwidth is not a must for my purpose, but heterodynes are
> very fatiguing. I could purchase a modern communications receiver, but
> these
> are expensive.

**No, they're not. Buy one and use a directional antenna.


--
Trevor Wilson
www.rageaudio.com.au

[[email protected]]

Trevor Wilson wrote:
> "Robert Morein" > wrote in message
> ...
> >I have an interest in sampling AM talk shows over a wide geographic
range.
> > At night, I can pick up many stations east of the Mississippi, and
some
> > all
> > the way to the Rockies.
> >
> > AM reception is generally plagued with whistles, known as
heterodynes,
> > that
> > are intermodulation products from stations on adjacent frequencies.
Some
> > communications receivers are equipped with notch filters and/or
digital
> > processing to remove these.
> >
> > Are there any tuners specifically for the AM "phile", that
incorporate
> > these
> > features. Wide bandwidth is not a must for my purpose, but
heterodynes are
> > very fatiguing. I could purchase a modern communications receiver,
but
> > these
> > are expensive.
>
> **No, they're not. Buy one and use a directional antenna.

It depends on what you consider expensive. But as a general rule:

1. True "communications receivers" offered today usually start around
a thousand dollars. Ten-Tec and Lowe have some less expensive models
and Ten-Tec has, or had, a kit that gave surprisingly good performance
for the price.

2. The audio sections of most of these radios suck, by audiophile
standards. Even in their heyday the ICOMs were popularly modded by
third party outfits so they would suck less.

3. Modern synthesized broadband HF receivers have, by necessity,
broadband front ends. This makes their typical 100/500 kHz-30 MHz
frequency range possible but at the expense of pure MW (AM BCB)
performance. The best vintage HF receivers can better the performance
of the SWL/ham grade synthesized rigs in nearly every parameter except
tuning stability (which on synthesized radios is wholly dependent on
the clock stability:nevertheless you won't find ovenized or even good
canned TCXO's there because a $3 crystal is cheaper...).

4. Perhaps the best commercially available MW receiver solution,
bizarrely enough, is the Potomac FIM field intensity meter, a small,
ruggedly built, and insanely overpriced (a French competitor is slowly
kicking their ass...)test box used to (relatively) precisely measure
broadcast AM stations' RF contours. One of the few good side effects of
Clear Channelization is that some of these come available on the used
market and may occasionally be seen in the low four figure ranges.

5. Probably for those for whom the Potomac FIM or perhaps the late
generation of full-DSP professional comm/monitoring solutions (Watkins
Johnson,Collins, et al) is out of range is a vintage comm receiver or
to undertake construction of a dedicated receiver oneself. You won't
need a screen room (wouldn't hurt...) but you will need a good RF
generator. The cheapest way as I said earlier might be to leverage the
technology employed in AM car radios when AM performance mattered: they
were the best MW receivers ever sold for connsumer use. The solid state
ones were quieter: the tube ones had better front end dynamic range
(except for the ones with 12-volt B+ tubes....)

[Ron]

On Mon, 7 Mar 2005 20:26:59 -0500, "Robert Morein"
> wrote:

>I have an interest in sampling AM talk shows over a wide geographic range.
>At night, I can pick up many stations east of the Mississippi, and some all
>the way to the Rockies.
>
>AM reception is generally plagued with whistles, known as heterodynes, that
>are intermodulation products from stations on adjacent frequencies. Some
>communications receivers are equipped with notch filters and/or digital
>processing to remove these.
>
>Are there any tuners specifically for the AM "phile", that incorporate these
>features. Wide bandwidth is not a must for my purpose, but heterodynes are
>very fatiguing. I could purchase a modern communications receiver, but these
>are expensive.
>

Depending on how technically oriented you are, there's a couple
of things you can do to your tuner:

First: many tuners are designed for wide bandwidth. If your is,
try re-aligning the IF for the narrowest possible pass band.

Second: you can build a small low pass filter -- at, say, 3KHz or
so. Power by the radio supply. Insert following the volume control.
Even 12 db/oct can do wonders to clear up the signal. A 24 db/oct
will only take a dual op-amp, 4 caps a 4 resistors and will be even
better.

-- Ron

[tcassette]

You might investigate the CCrane brand of AM radios and antennas. They
claim to be excellent for your purposes.
"Robert Morein" > wrote in message
...
>I have an interest in sampling AM talk shows over a wide geographic range.
> At night, I can pick up many stations east of the Mississippi, and some
> all
> the way to the Rockies.
>
> AM reception is generally plagued with whistles, known as heterodynes,
> that
> are intermodulation products from stations on adjacent frequencies. Some
> communications receivers are equipped with notch filters and/or digital
> processing to remove these.
>
> Are there any tuners specifically for the AM "phile", that incorporate
> these
> features. Wide bandwidth is not a must for my purpose, but heterodynes are
> very fatiguing. I could purchase a modern communications receiver, but
> these
> are expensive.
>
>

[[email protected]]

It's a false claim. I have owned three CCRadios and each has been
problematic, in addition the company has limited technical
resources-essentially it's only one tech, a Mr. Chris Justice. The
company exclusively advertises in crank magazines and on the Art Bell
show. Both Bell and frequent guest Wayne Green talk about their Amateur
Radio quals amongst the horse**** they discuss incessantly, proving how
far that Service has fallen. What few bench tech jobs are left in our
"electronic industry" tend to go to people that are _not_ hams, because
anymore an Amateur Radio license is a sign of lack of competence. It's
sad how that has become so.