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

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Reply
 
Thread Tools
Old 10th Jun 2021, 2:47 pm   #1
Cruisin Marine
Pentode
 
Join Date: Jul 2018
Location: London, UK
Posts: 127
Default Marconi TF2603 RF mV meter cal 6dB or not 6 dB

Hi have one of these RF Millivotltmenters that calibrates up fine on all ranges...except, it needs 6dB more drive to hit calibration than I would expect.

For example, if on any scale I increase my EMF Sig gen by 6dB then it all works fine.
So, to reach full scale on the 1mV scale, all is fine if I inject 2mV EMF, but it won't reach full scale with 1mV EMF.

I know some (maybe all?) of the early Marconi sig. gens used to output in PD and not EMF (So I always used a 6dB pad), I am wondering if my readings are out for this reason?

Is there anyone on here who owns one that can check to see if this is correct, I don't want to go fault finding if there isn't one.
Cheers.
Cruisin Marine is offline   Reply With Quote
Old 10th Jun 2021, 8:51 pm   #2
G0HZU_JMR
Nonode
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 2,435
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

Can I ask if you have a 50R sig gen and if you are terminating the sig gen output in an external 50R load? I have various fairly modern 50R sig gens here and they have the option of setting the level in V EMF or V PD.

If I set sig gen A to 1MHz and to a level of 20mV EMF and then terminate the sig gen with a good 50R load then I'd expect your Marconi meter to read 10mV when it probes across the 50R load.

If I set sig gen B to 1MHz and to a level of 10mV PD and then terminate the sig gen with a good 50R load then I'd expect your Marconi meter to also read 10mV when it probes across the 50R load.


So if I wanted to produce 10mV across the 50R load and I only had a sig gen that outputs V EMF then I'd have to turn the sig gen level up to 20mV EMF and make sure the external 50R termination is correctly fitted to the sig gen output before probing the 50R termination with your Marconi meter. I'd calibrate the meter to read 10mV in this case.
__________________
Regards, Jeremy G0HZU
G0HZU_JMR is offline   Reply With Quote
Old 10th Jun 2021, 9:04 pm   #3
Cruisin Marine
Pentode
 
Join Date: Jul 2018
Location: London, UK
Posts: 127
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

Hi Jeremy,
Thanks for the reply.
It is a Marconi 2019 50 ohm genny, it can only be set in EMF mode. It is directly terminated in to the 50 ohm RF millivoltmeter via the supplied N to probe adaptor.
Your comments agree with my thoughts on this one, but for one thing- I know the Racal RF Millivoltmeters (9301) agree with the level on the 2019, this Marconi does not, it reads 6dB less, hence my confusion.
THE problem is that the Marconi TF2603 manual doesn't specify whether it is reading from a PD or EMF genny for calibration purposes, not the first time I have encountered this.

I really need to hear from another TF2603 user to see what they have experienced, otherwise I am on a wild Goose chase.
It works fine otherwise, so I am happy.

Last edited by Cruisin Marine; 10th Jun 2021 at 9:14 pm.
Cruisin Marine is offline   Reply With Quote
Old 11th Jun 2021, 8:27 am   #4
Dickie
Octode
 
Join Date: Sep 2004
Location: St. Albans, Hertfordshire, UK.
Posts: 1,158
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

TF2603 uses a high impedance crystal detector, and just measures the PD applied to it. The source impedance is of no concern to it (at least until you get to VHF and above where stray C's come into play). If you have got a 50R termination across it that would explain the results you are getting.
__________________
Regards,

Richard, BVWS member

Last edited by Dickie; 11th Jun 2021 at 8:50 am.
Dickie is online now   Reply With Quote
Old 11th Jun 2021, 9:40 am   #5
Cruisin Marine
Pentode
 
Join Date: Jul 2018
Location: London, UK
Posts: 127
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

For the record, It is more or less flat response up to 400 MHz, and good to above 1 GHz.
The Racal equivalent uses a diode bridge on the input, but on the meter scale that READS 6dB higher than the Marconi TF2603.

This is rather pedantic in form, I am just trying to see some standard, if possible.

I need another TF2603 user to let me know if the Marconi should be reading the same or not really, or circuit design measurement notes could be confusing having two standards as it were... I guess it leads to notes on notes lol

Quote:
Originally Posted by Dickie View Post
TF2603 uses a high impedance crystal detector, and just measures the PD applied to it. The source impedance is of no concern to it (at least until you get to VHF and above where stray C's come into play). If you have got a 50R termination across it that would explain the results you are getting.

Last edited by Cruisin Marine; 11th Jun 2021 at 9:52 am.
Cruisin Marine is offline   Reply With Quote
Old 11th Jun 2021, 4:17 pm   #6
Cruisin Marine
Pentode
 
Join Date: Jul 2018
Location: London, UK
Posts: 127
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

I have sussed why my readings are down by 6dB.
The N to probe adaptor has a 50 ohm terminating resistor built inside, which I only saw upon close inspection.

There are TWO types of adaptor for those interested- there is the TM7950- straight through adaptor, and the other (which I have) is the TM7950- which is terminated with an internal 50 ohm resistor.
This explains the discrepancy between the Racal 9301 and the Marconi TF2603.
So now, both units give the same readings RELATIVE to a measured level at 50 ohms (this of course varies depending upon the impedance of the circuit being measured, but, that is life).

All is now rosy in the Garden now

Last edited by Cruisin Marine; 11th Jun 2021 at 4:23 pm.
Cruisin Marine is offline   Reply With Quote
Old 11th Jun 2021, 6:33 pm   #7
G0HZU_JMR
Nonode
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 2,435
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

Glad you got it sorted. It did seem at first like you could be using the V EMF sig gen with a 50R termination so that was my first query.

You could always reconfigure the 2019 to deliver V PD at the output and on the display if you prefer to work with V PD. I think this is possible on all the 2019 models but I can't be certain.

Note: You made a slight typo and wrote the same part number twice. I think the correct part numbers for the probe tip adaptor are TM 7949 for the terminated version and TM 7950 for the unterminated version.
__________________
Regards, Jeremy G0HZU
G0HZU_JMR is offline   Reply With Quote
Old 11th Jun 2021, 6:47 pm   #8
Cruisin Marine
Pentode
 
Join Date: Jul 2018
Location: London, UK
Posts: 127
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

Yeah, sorry, I did write the same part number twice- you are correct about the numbers you quoted.
I don't need to change the 2019 now really, as long as I know what I am measuring and decided everything is compatible, all is well (besides I lost the manual).
Mod's can you close this thread now please as the problem has been solved, many thanks all

Quote:
Originally Posted by G0HZU_JMR View Post
Glad you got it sorted. It did seem at first like you could be using the V EMF sig gen with a 50R termination so that was my first query.

You could always reconfigure the 2019 to deliver V PD at the output and on the display if you prefer to work with V PD. I think this is possible on all the 2019 models but I can't be certain.

Note: You made a slight typo and wrote the same part number twice. I think the correct part numbers for the probe tip adaptor are TM 7949 for the terminated version and TM 7950 for the unterminated version.
Cruisin Marine is offline   Reply With Quote
Old 11th Jun 2021, 6:53 pm   #9
Dickie
Octode
 
Join Date: Sep 2004
Location: St. Albans, Hertfordshire, UK.
Posts: 1,158
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

That's good. Manual can be downloaded free from here.
__________________
Regards,

Richard, BVWS member
Dickie is online now   Reply With Quote
Old 11th Jun 2021, 6:59 pm   #10
Cruisin Marine
Pentode
 
Join Date: Jul 2018
Location: London, UK
Posts: 127
Default Re: Marconi TF2603 RF mV meter cal 6dB or not 6 dB

Thanks Dickie- appreciated.
Cruisin Marine is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 2:22 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 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.