Electronic Goldmine has some Pulse Engineering LAN transformers (same as
those used on many LAN boards) on clearance at $1.00 each.
http://www.goldmine-elec-products.com/prodinfo.asp?number=G17078
Datasheet is at http://www.datasheet4u.com/download_new.php?id=541958

Quite cheap, in my opinion.

Cheers,
Dave M

Perry Sandeen via time-nuts wrote:

I'm not much further along then you but I did find a few things...

1. You can buy/salvage good quality 10.0 MHz transformers form networking
   equipment designed for 10BaseT Ethernet.  These are designed for galvanic
   isolation and are used in old 10baseT routers and switches.  Newer Ethernet
   works are 100 and 1000 Mhz but the older version was 10 MHz.  I have a box
   of salvaged parts I removed from junked routers.  These transformers are in
   wide DIP packages with 0.1" lead spacing.

2. Cheap 10MHz crystals need to be measured, sorted and matched by hand.
   And then you want to keep the temperature from moving around to much.
   Before I owned a GPSDO and a two channel scope I used to think the cheap
   crystals where all exactly "spot-on"

3. it is really easy to build a temperature controller using a $2 8-pin uP
   and a few lines of code.  The 8-pin uP will have a few analog inputs and
   outputs and even pins left over for status LEDs.

On Wed, Nov 26, 2014 at 8:08 PM, Perry Sandeen via time-nuts <
time-nuts@febo.com> wrote:

--

Chris Albertson
Redondo Beach, California

If you want to see how to really do it right, check out this
distribution Amp
on the TAPR site.

https://www.tapr.org/kits_tadd-1.html

73, Dick, W1KSZ

On 11/26/2014 9:08 PM, Perry Sandeen via time-nuts wrote:

Perry,

Just three days ago, I posted about my using transformers from
Ethernet cards. I also summarized the results of some measurements
using the spectrum analyzer. There was only one response, so it seems
that what I posted was widely ignored.

Dave M - good find on Electronic Goldmine.

Joe Gray
W5JG

On Thu, Nov 27, 2014 at 8:50 AM, Dave M dgminala@mediacombb.net wrote:

Any suggestions as to which chips, or links to any documentation?
Thanks,
Jim

On 11/27/2014 11:36 AM, Chris Albertson wrote:

This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

Hi

Just as you can “move” 455 KHz IF transformers down with a little padding, you can do the same thing with 10.7 MHz IF cans. They may or may not tune to 10 MHz. If you get some that don’t tune, it’s just a cap to bump them down.

The gotcha to any filter in a distribution system is Q. High Q implies high phase slope or long delay. In the real world things are temperature sensitive. Delta temp -> delta inductance -> delta phase -> bad ADEV. The trick is to get the job done with as low a Q as practical.

The next layer to the onion is loading. If the filter is on the output of the amp, it’s phase will change with load. Same issue as temperature, high Q -> big changes -> bad performance.

Even with a “class C” multiplier, fixed tuned Q< 10 circuits will do the trick for 5 -> 10 MHz doubling. With more exotic multipliers, even simpler filtering will do the job.

If you don’t need -200 db harmonics, and 30 db is fine — don’t go nuts with the filters.

Bob

Hi

We are talking about many different parts here and calling them all “transformers”.

The parts from an Ethernet line card are broadband devices used primarily for isolation. The 10.7 MHz IF transformers are designed for use in a filter. The first could be used to break a ground loop on a cable. The second could be used to knock out a harmonic or sub-harmonic. Each will do quite poorly trying to do the other one’s job.

Bob

I have 4 or 5 devices that use the 10 MHz from my Trimble Thunderbolt.
All but one have high impedance 10 MHz inputs, so the Thunderbolt
can drive the lot without any amplifier.

When I put together my Thunderbolt, power supply, and filter I assumed I
would
need a distribution amp ans made provisions for it.  Turns out it is not
necessary.

The real trick was locating well shielded patch cables to keep the
Thunderbolt from
jamming WWV on 10 MHz.

On 11/27/2014 08:41 AM, Richard Solomon wrote:

--
Chuck Forsberg WA7KGX  caf@omen.com  www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc      "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231  503-614-0430

For the most part, you don't want transformer isolation unless you plan on using balanced lines.  There are worse things than ground loops out there, and lifting a coax shield away from ground is a great way to find all of them.

You definitely don't want 10.7 MHz IF transformers, unless you are just trying to build a thermometer.

-- john, KE5FX
Miles Design LLC

Hi

Even if you are running 50 ohm loads, with 4 outputs, a power splitter is a very real solution. You will be down 6 db on each output. If you start with +13 you will have +7 dbm. Your target devices probably are happy as can be with anything over +3 dbm.

If you are worrying about WWVB problems, don’t just look at the cables. Check the connectors as well. BNC’s loose shielding capability much quicker than they get to a high insertion loss. I’ve had a lot of grief from them over the years.

Bob

Hi

You can also discover interesting things about the transformer it’s self in some circuits. They do what they do, but they also bring along a new set of issues. Sometimes simpler is better. If you don’t need what the transformer does, why add more complications ?

If you don’t lift the ground, the transformer isn’t doing much for you isolation wise.

If you do lift the ground, you need a lot more than just the transformer to make it all work and isolate properly. Once you add all that “stuff” you don’t have a simple circuit anymore.

——————

One example:

The most likely “threat” to your distribution system is a cell or portable phone. The beast fires up at random times and spews RF around everywhere. That’s the signal you want to isolate and shield against. It’s at some frequency between 40 MHz and 6 GHz depending on what it is. What ever you do needs to work over that range for isolation / shielding. It also needs to pass 10 MHz. Don’t have a phone in sight? How about WiFi, Bluetooth, and RF based remote controls ….

Why is it a threat? The RF comes back into your amp and changes bias levels / inter modulates with the 10 MHz. Either way, your 10 MHz moves around a bit. Is this purely theoretical? Nope, it happens far more often than you’d think. I’ve seen it a number of times.

A simple transformer at 10 MHz is not going to retain balance and isolation over 40MHz to 6 GHz. Even if it could the coax connector will imbalance it pretty badly. No balance = no isolation.

Good cables and a passive splitter have their issues, so do logic gates. Both have their advantages. More complicated is not always better.

23 dBm out of a KS box going down to +7 out gives you 16 db of room for attenuation. At 3 db for each 2:1 split, that’s 2^5 splits. It’s rare to find a need for 32 outputs. You can get 8 outputs at +13 dbm. That’s pretty hot for a distribution amp output.

Bob

Yep.  I found a lot of RF related issues appeared to go away when I switched to double shielded cables, stopped using T connectors for distributing signals, purchased and used HP distribution amps, terminated un used ports with 50 ohm loads etc.

I also found ferrite cores applied on the outside of longer cables to be helpful as well.  (I found it was useful to measure the actual currents flowing in the cable shields before and after adding the ferrite cores.)

I still have a couple of issues that occur when I occasionally transmit at the 300 watt level on VHF but the day to day issues where by WWV on 5 and 10 Mhz was hard to hear at times due to signal leakage and many low power transmissions could be counted on to influence a time lab frequency plot are gone now.

I expect issues are still there but they are below the detection threshold for me.  My time nuts gear and radio gear are separate but still in the same house.

Mark Spencer

On 2014-11-27, at 1:47 PM, Bob Camp kb8tq@n1k.org wrote:

Hi

If you are really going to get everything “tight” at RF, solid grounds (properly done) and good shielding (well thought out)  are going to do more for you than a lot of messing with circuits. Common mode chokes (outside cores) are way more likely to help than transformers.

That assumes you are after RF. If you have a 60Hz problem (due to the mega power AC welder) you may need to approach things a bit differently.

Bob

John wrote:

You certainly need the shield grounded at RF, but you don't
necessarily need it grounded all the way down to DC.  A fairly common
solution that works well for many applications is to use isolated
connectors (not connected directly to the chassis) with a 10nF
capacitor from each connector shield to the chassis immediately
adjacent to the connector.  The capacitor grounds the shield at RF
but allows very little current to flow at the mains frequency.  NOTE:
You want the bypass capacitor right at the connector, to make sure
the RFI current loop is tiny and cannot radiate.

That said, I often build distribution amplifiers with
chassis-grounded connectors and have never had ground loop
problems.  But then, I pretty much always design transformer-isolated
DC supplies with low-field transformers and linear regulators into
everything I build, and do not use wall-warts, desk-warts, or
switching supplies.

If one were building the dist amp I posted the other day and wanted
to use chassis-grounded connectors, the per-stage transformers could
be simplified from 1:1:1 to 1:1 -- omitting the third winding -- with
the transistor collectors capacitor-coupled to the output
connectors.  In this case, I would put ~100k resistors across each
output to hold the connector ends of the capacitors at 0v even with
an open load.

For isolation amplifiers used with mixer-type frequency comparators,
which can be very sensitive to ground loops because of the low mixer
output frequency, I do use RF transformers and bypass the shields to chassis.

Hear, hear.

Best regards.

Charles

Thanks for the kind words, Dick. :-)

However, a couple of notes on the TADD-1 bandpass filter:

1. I don't recommend installing it unless there is a good reason.  As
   others have noted, any tuned circuit is a thermometer and will degrade
   ADEV performance.  Other than the original test unit, I haven't built
   the filter into any of the several TADD-1s I've deployed in my lab.

2. The component values for the example filter in the TADD-1 manual are
   wrong.  I haven't gotten around to fixing that, mainly because of point 1.

And since the topic of isolated grounds has come up: the TADD-1 uses
transformer isolation on each input and output, and provides DC
isolation by putting a 10nf cap between ground and the coax shield (with
a very short path).  This seems to have worked pretty well for most users.

John

On 11/27/2014 11:41 AM, Richard Solomon wrote:

No problem, always glad to be of help to those in need.

73 es HH, Dick, W1KSZ

On 12/2/2014 2:27 PM, John Ackermann N8UR wrote: