Distribution amplifier project

Distribution amplifier project

Post by Foxs Mercantil » Wed, 06 Feb 2013 08:38:36



For several years I've been looking for a way to use a single
receiving antenna to feed several radios at once.

I've looked at the manuals for TMC equipment. Nice if you like
a rack mount full of vacuum tubes. Although they also made a
solid state version.

There seems to be a "black hole" on the internets about broad
band amplifiers that will cover .5 MHz to 30 MHz.

While browsing some older editions of the ARRL magazine QST, I
ran across a clever distribution amplifier, but the IC used is
no longer available.

A bit of research on the Maxim IC site and presto, the 4022
quad op amp. Pretty much a DC to 300 MHz quad amp with +6 dB
of gain running off + and - 5 volt supplies.

Being located in Ranger Texas, I don't have to worry about
having things like KNX 1070 AM or several FM stations within
overloading range of the amplifier.

Now off to gather supplies for a nice flat top antenna array
for the roof of the shop.

Jeff-1.0
wa6fwi

 
 
 

Distribution amplifier project

Post by Michael A. Terrel » Wed, 06 Feb 2013 10:04:45


Quote:

> For several years I've been looking for a way to use a single
> receiving antenna to feed several radios at once.

> I've looked at the manuals for TMC equipment. Nice if you like
> a rack mount full of vacuum tubes. Although they also made a
> solid state version.

> There seems to be a "black hole" on the internets about broad
> band amplifiers that will cover .5 MHz to 30 MHz.

> While browsing some older editions of the ARRL magazine QST, I
> ran across a clever distribution amplifier, but the IC used is
> no longer available.

> A bit of research on the Maxim IC site and presto, the 4022
> quad op amp. Pretty much a DC to 300 MHz quad amp with +6 dB
> of gain running off + and - 5 volt supplies.

> Being located in Ranger Texas, I don't have to worry about
> having things like KNX 1070 AM or several FM stations within
> overloading range of the amplifier.

> Now off to gather supplies for a nice flat top antenna array
> for the roof of the shop.

   Lots of Grass Valley video DA on Ebay going cheap.  I bought one for
99 cents + shipping.  It has two six output cards & the power supply. 75
ohm in & out, with BNC connectors.  Small rackmount.  There are Extron
units that are desktop versions. They were used with analog video
projectors and are being dumped as they projectors are updated. Some of
the video switches make a nice chassis for a DA.  I've seen these go for
$10:

http://www.ebay.com/itm/181072693514

   A well shielded aluminum case with a nice power supply & 50 BNC
connectors. The "System 10" has 60 BNC connectors. I want to build a GPS
disciplined 10 MHz frequency standard.

   BTW, I finally got Skype working on this computer, and a web cam.  I
allowed your request to skype me.

 
 
 

Distribution amplifier project

Post by Alex Pogosso » Wed, 06 Feb 2013 20:12:13



Quote:
> For several years I've been looking for a way to use a single
> receiving antenna to feed several radios at once.

> I've looked at the manuals for TMC equipment. Nice if you like
> a rack mount full of vacuum tubes. Although they also made a
> solid state version.

> There seems to be a "black hole" on the internets about broad
> band amplifiers that will cover .5 MHz to 30 MHz.

> While browsing some older editions of the ARRL magazine QST, I
> ran across a clever distribution amplifier, but the IC used is
> no longer available.

> A bit of research on the Maxim IC site and presto, the 4022
> quad op amp. Pretty much a DC to 300 MHz quad amp with +6 dB
> of gain running off + and - 5 volt supplies.

> Being located in Ranger Texas, I don't have to worry about
> having things like KNX 1070 AM or several FM stations within
> overloading range of the amplifier.

> Now off to gather supplies for a nice flat top antenna array
> for the roof of the shop.

> Jeff-1.0
> wa6fwi

10nV/SQRT(Hz) of noise -- it is 6K of equivalent noise resistance. Plus
about the half of that from the current noise 1.3pA/SQRT(Hz). It will not be
a sensitive preamp. But for the MW -- quite OK.
 
 
 

Distribution amplifier project

Post by Foxs Mercantil » Wed, 06 Feb 2013 23:37:44



Quote:
> 10nV/SQRT(Hz) of noise -- it is 6K of equivalent noise resistance. Plus
> about the half of that from the current noise 1.3pA/SQRT(Hz). It will not be
> a sensitive preamp. But for the MW -- quite OK.

Could you convert that to dBm as a rough estimate of "noise floor"

Jeff-1.0
wa6fwi

 
 
 

Distribution amplifier project

Post by Alex Pogosso » Thu, 07 Feb 2013 13:21:49



Quote:

>> 10nV/SQRT(Hz) of noise -- it is 6K of equivalent noise resistance. Plus
>> about the half of that from the current noise 1.3pA/SQRT(Hz). It will not
>> be
>> a sensitive preamp. But for the MW -- quite OK.

> Could you convert that to dBm as a rough estimate of "noise floor"

> Jeff-1.0
> wa6fwi

dBm - is a reference to absolute power which depends on the bandwidth, so it
is not very useful.
However, a noise figure is more illustrative.
The result will depend on the impedance matching. To achieve good results
you need to step up your antenna voltage to get about 5K of equivalent
resistance. This is difficult to achieve in a wide band (with a transformer
only), but easy with an antenna tuner/coupler device.

If your antenna is 75ohm in the band of your interest, try to use a 10:1 or
8:1 step-up transformer (this is turns ratio, not impedance ratio). If you
just plug a 75ohm cable to the input of the op-amp, you will have a noise
figure of 20dB -- very lousy performance. In other words, only signals at
least 10 times above the thermal noise floor can be discerned.

With a random wire or long wire antenna the noise figure can be better,
because the impedance is higher, but it is very unpredictable and reactive.
A solution to use an antenna tuner and work in a narrow band.

Alternatively you might try simply to use JEFEs as a source follower.
Connect two-three SST4416 in parallel to get a decent transconductance to
drive a 75ohm cable. Run them with Vgs=0 and Vds=5...8V. Total current will
be 30mA or so. Noise figure of such configuration will be low with any type
of an antenna. (LF cutoff is still needed.) You will not have voltage gain
though, but plenty of output RF current to feed several receivers not losing
the amplitude.

 
 
 

Distribution amplifier project

Post by Foxs Mercantil » Sat, 02 Mar 2013 12:33:09


My chip parts arrived this afternoon. I got 11 of them soldered
in place. Probably get the rest in tomorrow and apply power to
see what happens next.

The MAX4022:
<http://datasheets.maximintegrated.com/en/ds/MAX4014-MAX4022.pdf>
I'm using the sample circuit 1a, +6 dB gain on page 8.

I bought a handful of 1206 size chip resistors and capacitors.

Did you know you can actually breadboard with these using an 1/8"
tip on a Weller soldering station? I'm too lazy to put in a smaller
tip. ;-)

Like anything, it requires a steady hand, good eyesight (or at
least a decent magnifier) and a quick on quick off touch.

Jeff-1.0
wa6fwi

 
 
 

Distribution amplifier project

Post by Foxs Mercantil » Sun, 03 Mar 2013 12:47:49



Quote:
> Probably get the rest in tomorrow and apply power to
> see what happens next.

It works.

And it works rather nicely.

Even with -20 dBm in, no inter mods.
0.1 to 110 MHz.

Sweet.

Pix available on request.

Jeff-1.0
wa6fwi

 
 
 

Distribution amplifier project

Post by Michael Blac » Sun, 03 Mar 2013 13:08:44


Quote:


>> Probably get the rest in tomorrow and apply power to
>> see what happens next.

> It works.

> And it works rather nicely.

> Even with -20 dBm in, no inter mods.
> 0.1 to 110 MHz.

> Sweet.

> Pix available on request.

One time I wsa walking along and spied at the top of a public trash can
some sort of metal box that was clearly electronic.  I look closer, and
there are a bunch of them, and my guess was that they had to be cable
amplifiers.  They were certainly broad band with TO-5 "power transistors"
in them, and I can't think of anything else like that that would be in
such a public place.  It was like some guy had cleared out his cable truck
and dumped the amplifiers.

Their cases were certainly sturdy, not just the metal but built so rain
wouldn't get in.

I wish I could remember where I put them, I had a need for something like
that, and these had to be better than consumer type amplifiers.

   Michael

 
 
 

Distribution amplifier project

Post by Brenda Dye » Sun, 03 Mar 2013 14:05:01



Quote:


>> Probably get the rest in tomorrow and apply power to
>> see what happens next.

> It works.

> And it works rather nicely.

> Even with -20 dBm in, no inter mods.
> 0.1 to 110 MHz.

> Sweet.

> Pix available on request.

One time I wsa walking along and spied at the top of a public trash can
some sort of metal box that was clearly electronic.  I look closer, and
there are a bunch of them, and my guess was that they had to be cable
amplifiers.  They were certainly broad band with TO-5 "power transistors"
in them, and I can't think of anything else like that that would be in
such a public place.  It was like some guy had cleared out his cable truck
and dumped the amplifiers.

Their cases were certainly sturdy, not just the metal but built so rain
wouldn't get in.

I wish I could remember where I put them, I had a need for something like
that, and these had to be better than consumer type amplifiers.

   Michael

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

What you seem to be describing are line extender amps. If this is what they
are, you will need an inline AC or DC supply (depending on manufacturer)
that can be fed along with the input cable signal. These ran between 40 and
70 volts at a few amperes. The amps ARE fun to play with, as most have at
least a 4 volt output (some had 8!) and if you connect them to an antenna,
you can shoot a signal quite a ways!

 
 
 

Distribution amplifier project

Post by kimherro » Sun, 03 Mar 2013 21:49:50



Quote:

>> Probably get the rest in tomorrow and apply power to
>> see what happens next.

> It works.

> And it works rather nicely.

> Even with -20 dBm in, no inter mods.
> 0.1 to 110 MHz.

> Sweet.

> Pix available on request.

> Jeff-1.0
> wa6fwi

HI Jeff!!

Like to see what that looks like.  I'd like to do something similar

--
Kim Herron W8ZV

 
 
 

Distribution amplifier project

Post by Foxs Mercantil » Mon, 04 Mar 2013 12:08:47



Quote:
> Probably get the rest in tomorrow and apply power to
> see what happens next.

Well, I'm pretty happy with the way things tested with
the amplifier.

Using the Motorola R2018 Service Monitor for a source and
measuring the output with the HP 141Y spectrum analyzer I
measured the following:

At the lowest sweep range and bandwidth, the noise floor
of the 141T is about -123 dBm.

Connecting the amplifier to the spectrum analyzer did NOT
raise the noise floor. So to the best I can measure it, the
noise floor of the amplifier is below -123 dBm.

Note: 50 uV at 50 ohms = -73 dBm (S9)
          0.2 uV at 50 ohms = -121 dBm (S1)

I could STILL see a signal down to -120 dBm on the spectrum
analyzer.

Raising the signal level up to -60 dBm and sweeping it from
0.1 to 110 MHz, I saw no noticeable droop or peaks in the
response. So I'm going to call it flat from 0.1 to 110 MHz.
The MAX4022ESD is rated flat out to 200 MHz and it appears
that it is indeed flat. (Or at least flat to +/- 1 dB or so.)

Overall gain of each of the four amplifier stages appears to
be -4 dB.

Raising the signal level to -30 dBm and summing a second
signal at -30 dBm produced no determinable inter modulation
products.

Note: -30 dBm is equivalent to S9 +43 dB, quite the hefty
pair of signals.

I think I can live with that. ;-)

Jeff-1.0
wa6fwi