Topics

Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603


Attilio
 

Dear Sirs,
I got hold of a 7L13 spectrum analyzer in a 7603 mainframe and I have two questions to ask you, first from the manual the tuning knob can be pushed or pulled to change the tuning speed, but on my 7L13 the tuning knob is fixed and there is only the word tuning,
Do you know when this modification was made and why ?
Second question: Is it possible to extend the maximum frequency from 1.8 GHz to 2.5 GHz ?
If so, what are the changes to be made ?

Thanks a lot to everyone, a greeting
Attilio


Chuck Harris
 

I can't say about the push/pull tuning knob, only that it is easy
to break, hard to fix, and adjust... perhaps yours got broken and
this is the best fix easily done?

I think what you are looking at is a 7L12 knob, and perhaps
everything behind it.

The 7L13 has a high IF frequency of about 2.5GHz. The 2.5GHz
modification removes the roofing filter from the RF input, allowing
signals up to 2.5GHz and beyond to enter the mixer... Without the
roofing filter, these signals pass right through into the IF
amplifier, where they lift the entire band.

Basically, you can count on seeing your router, bluetooth, and your
microwave oven take over your SA whenever they happen.

I wouldn't want a 7L13 with the 2.5GHz modification.

It is a nice little SA, best keep it nice.

-Chuck Harris

Attilio wrote:

Dear Sirs,
I got hold of a 7L13 spectrum analyzer in a 7603 mainframe and I have two questions to ask you, first from the manual the tuning knob can be pushed or pulled to change the tuning speed, but on my 7L13 the tuning knob is fixed and there is only the word tuning,
Do you know when this modification was made and why ?
Second question: Is it possible to extend the maximum frequency from 1.8 GHz to 2.5 GHz ?
If so, what are the changes to be made ?

Thanks a lot to everyone, a greeting
Attilio







Attilio
 

Thank you very much Chuck, I will not make the change to bring it to 2.5 GHz, instead I wanted to ask you what is the real analysable minimum frequency, I have seen that approaching 1 kHz it becomes difficult to visualize the signal due to the proximity of the internal local oscillator carrier .

As for the Tuning control, I assure you that everything looks original and on the front there is only the word TUNING and not PUSH / PULL.
I don't know what to say about it.

Greetings
Attilio


Chuck Harris
 

Hi Attilio,

It has been about 15 years since I sold my 7L5, 13, and 18,
and bought an HP 8566B. I liked the 7L stuff, but the HP is
orders of magnitude better to work with.

The original knob had a clutch in it, and was used to fine
tune the analyzer when the unit was in the narrow bandwidth
phase locked settings with narrow filters. I think the 7L12
left off the narrow filters, and the phase lock hardware, and
maybe yours had that done as well?

Close to the bottom of the band, the LO is almost at the IF
frequency, and swamps anything that comes in the RF port.

LO - IF = RF, so at 1KHz, the LO is 1KHz above the IF frequency.

You really shouldn't expect much from a 7L13 at the lowest
frequencies. It is more a 1MHz to 1.8GHz analyzer. It does
a nice job characterizing HF, VHF, and UHF signal sources.

Similarly, you can't tell much about a very high frequency
source, as any harmonic content will be out of the range of
the analyzer.

-Chuck Harris

Attilio wrote:

Thank you very much Chuck, I will not make the change to bring it to 2.5 GHz, instead I wanted to ask you what is the real analysable minimum frequency, I have seen that approaching 1 kHz it becomes difficult to visualize the signal due to the proximity of the internal local oscillator carrier .

As for the Tuning control, I assure you that everything looks original and on the front there is only the word TUNING and not PUSH / PULL.
I don't know what to say about it.

Greetings
Attilio






Attilio
 

You're right Chuck, I think it's great from 1 MHz and that at very high frequencies there is the problem of not being able to see the harmonics.
But I fell in love with the 7L13 and will use it in HF, VHF and UHF where I think it gives its best.

I took off the TUNING knob and noticed that it is heavy so it acts like a flywheel when tuning.
I think the only way to find out the truth is to ask someone who worked at Tektronix and knows the whole story of 7L13.

Thanks a lot Chuck.
Greetings
Attilio


Chuck Harris
 

Another way, possibly, is to scan through the catalogs
from about 1978 through 1981.

I looked in my 1981 catalog, and I find that I am misremembering
a lot of things about the 7L13 and 12.

-Chuck Harris

Attilio wrote:

You're right Chuck, I think it's great from 1 MHz and that at very high frequencies there is the problem of not being able to see the harmonics.
But I fell in love with the 7L13 and will use it in HF, VHF and UHF where I think it gives its best.

I took off the TUNING knob and noticed that it is heavy so it acts like a flywheel when tuning.
I think the only way to find out the truth is to ask someone who worked at Tektronix and knows the whole story of 7L13.

Thanks a lot Chuck.
Greetings
Attilio







Miguel Work
 

If you look inside the 7l13 there are two multiturn pots, fine and coarse, mechanically connected to the tuning knob. Each pot has a electromagnet clutch. The pot engaged depends of span resolution position, or pll on/off position. For a low span the fine pot is automatically engaged, but if you switch off pll, coarse pot is engaged, so tuning knob will move more frequency. For large span coarse pot is used.

7L12 and 491 has PLL too, but the PLL in 491 isn´t automatic



https://www.youtube.com/watch?v=832QaqG7OPI
https://www.youtube.com/watch?v=G3A-4Jrtv3s



Regards!




-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Attilio
Enviado el: lunes, 21 de diciembre de 2020 19:28
Para: TekScopes@groups.io
Asunto: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Dear Sirs,
I got hold of a 7L13 spectrum analyzer in a 7603 mainframe and I have two questions to ask you, first from the manual the tuning knob can be pushed or pulled to change the tuning speed, but on my 7L13 the tuning knob is fixed and there is only the word tuning, Do you know when this modification was made and why ?
Second question: Is it possible to extend the maximum frequency from 1.8 GHz to 2.5 GHz ?
If so, what are the changes to be made ?

Thanks a lot to everyone, a greeting
Attilio








Scanned by McAfee and confirmed virus-free.
Find out more here: https://bit.ly/2zCJMrO


Chuck Harris
 

You are of course right. My recollection of a fancy knob
on the 7L13 was the time/division knob, which is similar to
the time/division knobs on all of the other scopes of the
era.

I think the OP's 7L13 is typical of all 7L13's. If there is
a push/pull notation in the manual, it is probably wrong.

-Chuck Harris

Miguel Work wrote:

If you look inside the 7l13 there are two multiturn pots, fine and coarse, mechanically connected to the tuning knob. Each pot has a electromagnet clutch. The pot engaged depends of span resolution position, or pll on/off position. For a low span the fine pot is automatically engaged, but if you switch off pll, coarse pot is engaged, so tuning knob will move more frequency. For large span coarse pot is used.

7L12 and 491 has PLL too, but the PLL in 491 isn´t automatic



https://www.youtube.com/watch?v=832QaqG7OPI
https://www.youtube.com/watch?v=G3A-4Jrtv3s



Regards!




-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Attilio
Enviado el: lunes, 21 de diciembre de 2020 19:28
Para: TekScopes@groups.io
Asunto: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Dear Sirs,
I got hold of a 7L13 spectrum analyzer in a 7603 mainframe and I have two questions to ask you, first from the manual the tuning knob can be pushed or pulled to change the tuning speed, but on my 7L13 the tuning knob is fixed and there is only the word tuning, Do you know when this modification was made and why ?
Second question: Is it possible to extend the maximum frequency from 1.8 GHz to 2.5 GHz ?
If so, what are the changes to be made ?

Thanks a lot to everyone, a greeting
Attilio








Scanned by McAfee and confirmed virus-free.
Find out more here: https://bit.ly/2zCJMrO





Brian J. Henry
 

Hi Attilio,

The 7L13 is spec’d down to 1 kHz. It is able to go down this low because the first mixer is DC coupled to the RF input. The downside to this is that any DC at the RF input will destroy the first mixer. Unless you are specifically using it for very low frequencies, it is a good idea to place a DC block in series with the RF input in order to afford it some protection.

To protect the first mixer, Tektronix added a “limiter” to the RF input circuitry when they introduced the 7L14. The 7L14 is spec’d down to 10 kHz with the option of deleting the “limiter” and DC coupling the input to bring it down to 1 kHz.

The 2.5 GHz option for the 7L13 is designated “MOD 139U”. I don’t believe that it was ever listed as an option in a Tektronix catalog. It was offered as a option for the 7L14, however. Chuck pretty much calls it right as to how it was implemented and what the downsides are.

To take advantage of the 7L13’s narrow resolution bandwidth filter capabilities, you will want to install it into a storage oscilloscope as it is next to impossible to use the 30 Hz resolution bandwidth filter without one.

The 7L14 resolved this necessity with the introduction of digital storage. For all practical purposes, the 7L14 is identical to the 7L13 except for the inclusion of digital storage.

There is an early and a late version of the 7L13. They are differentiated by the introduction of an LED readout for the reference level.

I believe that the earliest 7L13’s (or prototypes) used the push/pull knob arrangement for selecting the fast/slow tuning that is described in the manual. I have never actually seen one. Every one that I have seen uses the innovative dual clutch system to engage and disengage the two tuning potentiometers.

When the frequency span is 100 kHz/division and greater it operates in the fast tune mode. At 50 kHz/division and below, it operates in the slow tune mode when the spectrum analyzer is phase locked.

The phase lock circuitry can be disabled with a front panel switch. When this is done, the analyzer reverts to the fast tune mode.

Each iteration of the 7L series spectrum analyzers brought with it new innovations that are well documented in the Tekscopes articles that accompanied their introductions that are quite informative. Tektronix managed to package a considerable amount of functionality into relatively small spaces for the time. It isn’t really fair to compare them with the huge HP spectrum analyzers that were their contemporaries.

I hope that you find some of this information to be of help.

Brian Henry


Miguel Work
 

I use external mixer and CW generator, 1Ghz in this example, to go at higher frequencies.

For example, a DECT signal from cordless phone:

https://www.youtube.com/watch?v=8fp1UvMKQPI




-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Brian J. Henry
Enviado el: miércoles, 23 de diciembre de 2020 17:54
Para: a.alovisetti@alice.it; TekScopes@groups.io
Asunto: Re: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Hi Attilio,

The 7L13 is spec’d down to 1 kHz. It is able to go down this low because the first mixer is DC coupled to the RF input. The downside to this is that any DC at the RF input will destroy the first mixer. Unless you are specifically using it for very low frequencies, it is a good idea to place a DC block in series with the RF input in order to afford it some protection.

To protect the first mixer, Tektronix added a “limiter” to the RF input circuitry when they introduced the 7L14. The 7L14 is spec’d down to 10 kHz with the option of deleting the “limiter” and DC coupling the input to bring it down to 1 kHz.

The 2.5 GHz option for the 7L13 is designated “MOD 139U”. I don’t believe that it was ever listed as an option in a Tektronix catalog. It was offered as a option for the 7L14, however. Chuck pretty much calls it right as to how it was implemented and what the downsides are.

To take advantage of the 7L13’s narrow resolution bandwidth filter capabilities, you will want to install it into a storage oscilloscope as it is next to impossible to use the 30 Hz resolution bandwidth filter without one.

The 7L14 resolved this necessity with the introduction of digital storage. For all practical purposes, the 7L14 is identical to the 7L13 except for the inclusion of digital storage.

There is an early and a late version of the 7L13. They are differentiated by the introduction of an LED readout for the reference level.

I believe that the earliest 7L13’s (or prototypes) used the push/pull knob arrangement for selecting the fast/slow tuning that is described in the manual. I have never actually seen one. Every one that I have seen uses the innovative dual clutch system to engage and disengage the two tuning potentiometers.

When the frequency span is 100 kHz/division and greater it operates in the fast tune mode. At 50 kHz/division and below, it operates in the slow tune mode when the spectrum analyzer is phase locked.

The phase lock circuitry can be disabled with a front panel switch. When this is done, the analyzer reverts to the fast tune mode.

Each iteration of the 7L series spectrum analyzers brought with it new innovations that are well documented in the Tekscopes articles that accompanied their introductions that are quite informative. Tektronix managed to package a considerable amount of functionality into relatively small spaces for the time. It isn’t really fair to compare them with the huge HP spectrum analyzers that were their contemporaries.

I hope that you find some of this information to be of help.

Brian Henry







Scanned by McAfee and confirmed virus-free.
Find out more here: https://bit.ly/2zCJMrO


Attilio
 

Thanks a lot to everyone
Brian clarified my doubts, Miguel you are light years ahead of me, Chuck thanks for the support.
I took a look at Morris Engelson's book "Spectrum Analyzer Measurement - Theory and Pratice" and felt like a caveman, but how much do these engineers know?

Greetings
Attilio


tinkera123
 

FYI .... I have a 7L13, TUNING functions as per dual clutch mechanism described above, TUNING dial max 1.878GHz, Build no: B 133,021.

Merry Xmas to all ...


--
Cheers,
Ian,
Melbourne, Australia


Attilio
 

Thanks tinkera123, I think my 7L13 is similar to yours. My 7L13 has the mechanical indicator for the reference level, but I know the latter had the LED display for the reference level indication.

Greetings and Merry Xmas to all


Attilio
 

Sorry if I ask some trivial questions, but I am worried by the writing on the RF input of the 7L13 regarding the absolute prohibition of applying a direct current voltage (0 Vdc). I am looking on the internet for a dc-blocking with BNC connectors to be applied on the RF input, but I cannot find the Tektronix part number 015-0221-00, I was thinking of using a small metallic box with BNC connectors and connecting a 1000 pF - 1 KV ceramic capacitor between the BNC connectors, what do you think?
I have seen other DC blockers use a 100nF capacitor but I doubt that when charging it will damage the 7L13's first mixer.
I should equip myself with some accessories, but I have no clear ideas, I should buy a power splitter or a combiner.
I would like to buy a TR502 tracking generator with its power supply in the future.

Greetings and Merry Xmas to all


Miguel Work
 

Tte cheap opción if bandwith os importante os a BNC ti SMA adaptar and a SMA DC blocker


Chuck Harris
 

A couple of things:

First, you don't have to get so worried about accidentally putting
DC on the mixer. It is safer, and better to be more conscious of
what you are doing when you make measurements with your SA. Sample
the measurement point with an oscilloscope, to determine the signal
composition, before connecting your SA. Always use the maximum
attenuation that allows you to get your measurement. Make prophylactic
use of probes and loops. Always discharge coaxial lines before you
attach them to the SA.

Second, DC blocks will *NOT* protect your SA against all such DC
abuses. When a discharged capacitor is connected to a high voltage
point, it will instantaneously behave as a dead short circuit. It
will transfer that high voltage point directly to your mixer, as if
it isn't there. Only as the capacitor begins to charge, will that
high voltage/current be removed from the mixer.

If you connect your DC block protected SA input to a 100V point inside
of a transmitter, it will toast your mixer very nicely, and quickly.

Train yourself to use your SA safely. Don't rely on crutches to protect
you from unsafe behavior.

-Chuck Harris

Attilio wrote:

Sorry if I ask some trivial questions, but I am worried by the writing on the RF input of the 7L13 regarding the absolute prohibition of applying a direct current voltage (0 Vdc). I am looking on the internet for a dc-blocking with BNC connectors to be applied on the RF input, but I cannot find the Tektronix part number 015-0221-00, I was thinking of using a small metallic box with BNC connectors and connecting a 1000 pF - 1 KV ceramic capacitor between the BNC connectors, what do you think?
I have seen other DC blockers use a 100nF capacitor but I doubt that when charging it will damage the 7L13's first mixer.
I should equip myself with some accessories, but I have no clear ideas, I should buy a power splitter or a combiner.
I would like to buy a TR502 tracking generator with its power supply in the future.

Greetings and Merry Xmas to all






Attilio
 

Thanks Chuck, you made it clear that I don't have to rely on a DC blocker, but I have to be the first protection of the 7L13's first mixer.
I keep in mind all your considerations.
I understood that accessories with SMA connectors cost less and are more available than those with BNC connectors, so the first I will have to buy is a BNC male to SMA female adapter.
Considering that I would like to use the SA mainly for measurements on receivers (maximum frequency 900 MHz), what accessories should I buy to use with my SA ?

I am looking on the internet for a TR502 (Tracking Generator) with its power supply.
I may have found a 7613 mainframe that has STORE mode.

Greetings and Happy Holidays
Attilio


Attilio
 

Thanks Miguel in fact I think I buy a BNC male to SMA female adapter.

Greetings and happy holidays
Attilio


tinkera123
 

Just as I always try to remember to set my Scope coupling to Grd and Vertical amp to min sensitivity ... I do the same with SA ie max Attenuation at 'turn-off'.
Also, I have built my own DC block with BNC connectors, and diodes to take out voltage spikes (circuit suggestions are on web) ... again, not foolproof.
Cheers, Ian

--
Cheers,
Ian,
Melbourne, Australia


Nenad Filipovic
 

On Sat, Dec 26, 2020 at 10:42 AM, Attilio wrote:
I may have found a 7613 mainframe that has STORE mode.
Using 7L* SAs in 7854 is a song. It's not just the digital storage, it's the averaging that can significantly help smooth the measurement and increase your SNR. I do it all the time with my 7L5 and also 7L13. Getting a 7854 would really help.

I am looking on the internet for a TR502 (Tracking Generator) with its power supply.
TR502 is great, but you can also do much with a noise source which you can get cheaply on eBay. Most will cover the full frequency range of the 7L13.

what accessories should I buy to use with my SA ?
Certainly not among the first things you should try with your SA, but I can't skip mentioning it - the P6201 or a similar active probe. It would replace the low 50ohm input impedance of your SA with a high impedance low capacitance load. It can greatly help debug/calibrate the high impedance RF circuits (receiver IFs, mixers...). Note that using an active probe with your SA kind of quadruples the danger of killing your mixer with accidental DC, so the utmost care is necessary.

Best regards and Happy Holidays,
Nenad FIlipovic