UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 10th Dec 2017, 7:23 pm   #1
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, south Somerset, UK.
Posts: 5,990
Question Hatfield modulator: info.?

As per photos. Can anyone here tell me more about it and typical uses, please?
It's called a 'modulator' and it does indeed look like some form of a 4-diode balanced modulator. I made some measurements and did some tests:

D.C. resistances:
Port A to gnd.: v.low.
Port B to gnd.: v. high.
Port C to gnd.: v.low.
Port A - port C: low.
Port A - port B: high.
Port B- port C: high.

Signal tests.
Port A: Input: 10 MHz C.W. @ 100 mV rms
Port B: Input: 10 kHz C.W. @ 100 mV rms
Port C: Output: 100% A.M. modulated waveform, distorted. Envelope freq. of 20 kHz.

The signal tests were simply inspired guesses as to what to feed in where and how much. The 'guesses' were simply because I don't know enough about this item to make what probably should have been sensible connections, etc. Which takes us back to where I came in: I would like to discover more about this item. A cct. diag. would be useful.

Any knowledgeable members here?

Al.
Attached Thumbnails
Click image for larger version

Name:	HATMOD1.jpg
Views:	85
Size:	40.2 KB
ID:	153752   Click image for larger version

Name:	HATMOD2.jpg
Views:	75
Size:	44.0 KB
ID:	153753  
__________________
"Your idea is crazy! But the question is this: is it crazy enough . . . . to be true?" (Niels Bohr)
Skywave is offline  
Old 10th Dec 2017, 7:46 pm   #2
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 6,374
Default Re: Hatfield modulator: info.?

Does look like some form of DBM.

DC measurements are likely only to see the resistances of the windings on the toroidal transformers.


I've seen these sorts of things used as 'downconverters' ahead of HF testgear in order to extend the range to VHF/UHF.

200-500MHz into one port, a switched-tuned reference oscillator in the same sort of range to another port, a 5MHz-rated scope or similar on the output-port.

Some catalogs etc here: http://www.collection.archivist.info...nstruments+Ltd which might be useful searching ground.
G6Tanuki is online now  
Old 10th Dec 2017, 9:50 pm   #3
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, south Somerset, UK.
Posts: 5,990
Question Re: Hatfield modulator: info.?

G6T: thanks.

The only reason I included the d.c. resistance measurements is in the hope that someone might be able to use those in order to assist the production a cct. diag.
Unfortunately, your suggested link did not provide any info.

As for my signal tests, the only reason I used an audio / L.F. signal on one port was because of this device's name: 'modulator' - and, in retrospect, that tripped me up. To me, 'modulation' should refer to modulation such as A.M., F.M., P.W.M., P.C.M. etc. So on that basis, I feel that a 'D.B.M.' - which is what this is - should be known as a 'mixer' - a 'double-balanced mixer'. Anyway, that as maybe: a further discussion about that is not relevant to this thread.

This device - a D.B.M. - has four toroids: any idea why four? Usually two are sufficient.
The fact that this device has 3 BNC sockets, to me, says that this is an 'all R.F. device' - with a typical usage as you have suggested.
So, developing that line of thought, of the 3 ports, A, B and C, which one becomes the O/P port?

Al.
__________________
"Your idea is crazy! But the question is this: is it crazy enough . . . . to be true?" (Niels Bohr)
Skywave is offline  
Old 10th Dec 2017, 10:07 pm   #4
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 6,374
Default Re: Hatfield modulator: info.?

Some DBMs use a bifilar common-mode choke [which could be wound on a toroid] - and which may be described as a 'balun' on some ports ... it improves balance of the main toroid-driving-the-diode-quad.

If this is the case I'd be expecting two of the toroids to have three windings (the ones connected direct to the diodes as in the classic DBM input/output circuit) and two of the toroids to have only two windings.

As an example see fig.10 here: http://www.robkalmeijer.nl/techniek/...991/04/page39/

where L6 and L8 are the common-mode chokes.

There are other possible 'networks' you could find in these things for impedance-matching/power-division/combination.

As to which is the input and which is the output - it may well be symmetrical!

Last edited by G6Tanuki; 10th Dec 2017 at 10:19 pm.
G6Tanuki is online now  
Old 10th Dec 2017, 10:14 pm   #5
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 6,890
Default Re: Hatfield modulator: info.?

A snippet from Google books:

"Hatfield are good mixers Hatfield double- balanced modulators and mixers for 50 -ohms systems are available for immediate delivery.The 1700 Series can be used as an amplitude modulator, mixer, phase detector or current controlled V.H.F. attenuator There are also encapsulated versions for printed circuit mounting. • Excellent balance • Low noise factor • Wide band • P.C.B"

Lawrence.
ms660 is online now  
Old 10th Dec 2017, 10:24 pm   #6
G8HQP Dave
Dekatron
 
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,441
Default Re: Hatfield modulator: info.?

In the case of AM and DSB there is no difference between a 'modulator' and a 'mixer'. The terms are completely interchangeable.

The resistance measurements suggest that ports A and C are transformer coupled, and port B goes straight to the diodes. This is fairly common. It means that port B can be used down to DC. What is 'input' and 'output' is largely up to the user, although some ports may have slightly better performance in one role. To get the idea, look at a MiniCircuits catalogue or datasheet.
G8HQP Dave is offline  
Old 11th Dec 2017, 12:42 am   #7
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, south Somerset, UK.
Posts: 5,990
Default Re: Hatfield modulator: info.?

Quote:
Originally Posted by G8HQP Dave View Post
In the case of AM and DSB there is no difference between a 'modulator' and a 'mixer'. The terms are completely interchangeable.
Yes, yes: I am well aware of that. But that was not my point: I was simply expressing my viewpoint of the terminology as used and applied.

I have no intention of discussing this aspect of this thread any further, since it is off-topic for the thread - but I appreciate your contribution to it. However, if you would like to further the discussion about the appropriate usage of the words 'mixer' and 'modulator' and start a new thread so to do, I will be happy to contribute to it.

Al.
__________________
"Your idea is crazy! But the question is this: is it crazy enough . . . . to be true?" (Niels Bohr)
Skywave is offline  
Old 11th Dec 2017, 12:56 pm   #8
G8HQP Dave
Dekatron
 
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,441
Default Re: Hatfield modulator: info.?

The distinction between those two names for the same device would seem to be very much on topic for this thread, but there is nothing more to be said except that the name commonly used depends only on the application of the device in that particular system.
G8HQP Dave is offline  
Old 11th Dec 2017, 9:24 pm   #9
Jon_G4MDC
Hexode
 
Jon_G4MDC's Avatar
 
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 471
Default Re: Hatfield modulator: info.?

For sure Port B is the IF port and looks to be DC Coupled.
Ports A and C appear similar and could be LO&RF probably almost interchangeable.
Single diode ring so probably for about +7dBm / 5mW LO Drive.
For testing drive it harder than described above.

Nice at HF - not sure about 300MHz upper limit though.

Last edited by Jon_G4MDC; 11th Dec 2017 at 9:30 pm.
Jon_G4MDC is offline  
Old 11th Dec 2017, 10:35 pm   #10
G0HZU_JMR
Octode
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 1,486
Default Re: Hatfield modulator: info.?

It looks to me like a classic (double balanced) diode ring mixer but they have added baluns at the LO and RF port to optimise it for modulator use.
Ideally, you would want high isolation between ports A and C if you want a modulator like this to be able to act as a decent On Off Keying (OOK) modulator that has a decent 'off' performance. It looks like the two input transformers are twisted wire TLTs. This will help provide good balance up through the VHF region. Are the inner transformers trifilar wound?

I'd advise against moving the windings in your attempts to reverse engineer the circuit. Someone at the factory probably nudged/tweaked the windings to get the best isolation between ports A and C across the full RF range. So best left alone.

As Jon says, the LO drive level is probably +7dBm. You can use this as a classic DSB SC modulator or for AM if you allow a small DC offset current to be bled into port B along with the modulation. This will spoil the balance and allow a carrier to leak to the RF port and this will create AM. You can also use it as an attenuator by feeding in a DC current to port B.
Or you can switch in positive and negative current (-5mA/+5mA as a square wave) to port B to make a BPSK modulator. Or use it for OOK if you just switch in 0mA / 5mA at port B to turn the RF on and off between ports A and C.

I'm not sure what the diodes are rated for but I'd be very careful not to overdrive port B. Probably best kept to a few mA modulator drive here? The circuit is probably something like the one below but I am just guessing.
Attached Thumbnails
Click image for larger version

Name:	Hatfield DBM.jpg
Views:	22
Size:	18.7 KB
ID:	153840  
__________________
Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 11th Dec 2017 at 10:48 pm.
G0HZU_JMR is offline  
Old 11th Dec 2017, 10:46 pm   #11
G0HZU_JMR
Octode
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 1,486
Default Re: Hatfield modulator: info.?

It's a neat and versatile little device to have in the workshop so I'd advise caution when testing it to reverse engineer what it can do. Maybe fit an external series+shunt current limiting resistor network at port B of maybe 1000R in series with the generator and 47R shunt (across port B) to allow you to safely connect a function generator and play with typical modulator waveforms of a few volts pkpk?

You could then (safely) drive it with various waveforms from the function generator to create AM or DSB SC or BPSK or OOK? This would limit the diode current to a few mA. If you try generating BPSK with it I think it will generate classic/crude BPSK but this will have phase discontinuities at the switching points. So best to limit the rise/fall time of the square wave. The same applies to the OOK square wave. You can think of BPSK as two OOK waveforms (180deg out of phase) that are interlaced together. Each phase is effectively being on/off keyed (to be replaced by the other phase) so there will be a classic key click issue just like with OOK or morse code unless the modulation rise/fall time is shaped to minimise interference to other users.
__________________
Regards, Jeremy G0HZU

Last edited by G0HZU_JMR; 11th Dec 2017 at 11:04 pm.
G0HZU_JMR is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:37 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.