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Hi list

I'm using my 7L13 to measure bursts of 480 MHz signals.
It works pretty well but I miss a more precise frequency readout.
Is it possible to make a better frequency readout?

Is it difficult to either:
1. Mix the first LO with an external 2095MHz source and insert into a
frequency counter.
2. Replace the YIG oscillator with a digital signal source.

As you may have found out by now, I am a bit of a novice in RF :)

Regards
Gudjon

On Fri, Jul 27, 2018 at 11:18 PM, Gudjon Gudjonsson wrote:

I'm using my 7L13 to measure bursts of 480 MHz signals.
It works pretty well but I miss a more precise frequency readout.
Is it possible to make a better frequency readout?

Is it difficult to either:
1. Mix the first LO with an external 2095MHz source and insert into a
frequency counter.

This is basically what the TR502 and similar tracking generators do. They're designed to solve exactly this problem. However, just mixing with the first LO isn't enough. At frequency/div settings less than 200kHz/div (I think) the first LO is fixed and the second LO is swept, so you need to use both LOs to extract the signal frequency. So if 'precise' to you means better than 100kHz accuracy, you need to take both LOs into account.

2. Replace the YIG oscillator with a digital signal source.

I wonder - maybe this could work, if you can find a signal source covering 2.1-3.9GHz. However, you'll need to measure the second LO too.

The cheapest way of measuring the signal frequency is probably just to measure both LOs with frequency counters and then do the math, as they say. I found that my old but great HP 5245L counter with a 5254A 0.3-3GHz frequency converter plugin (plugin was $20 on ebay - there are still bargains out there!) does a fine job of measuring the local oscillator frequencies.

Chris

Thanks for the answer Chris

You made things a bit clearer.

I don't need accuracy, just stability. I do have a frequency source
that I can use to tune into the frequency I'm after
but then I would like to keep this stable.

In zero span mode I should be able to use a frequency counter on the
1st LO. I found one for frequencies up to
5.8GHz for a reasonable price.

In scanning mode I will try to read the DVM input voltage (U2140) with
a more precise external
DVM and see if I can use it for some improvement.

I will test and let you know if it works.

Regards
Gudjon

Hi, I have a 7L12 and a 7L14 and I made my self the same question. With two prescalers and two counters is possible to make a circuit and write in the readout system. Anyway I?m searching for a TR502 system with counter.

Regards

Miguel

-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Gudjon Gudjonsson
Enviado el: sábado, 28 de julio de 2018 15:54
Para: TekScopes
Asunto: Re: [TekScopes] 7L13, more exact frequency readout

Thanks for the answer Chris

You made things a bit clearer.

I don't need accuracy, just stability. I do have a frequency source that I can use to tune into the frequency I'm after but then I would like to keep this stable.

In zero span mode I should be able to use a frequency counter on the 1st LO. I found one for frequencies up to 5.8GHz for a reasonable price.

In scanning mode I will try to read the DVM input voltage (U2140) with a more precise external DVM and see if I can use it for some improvement.

I will test and let you know if it works.

Regards
Gudjon

On Sat, Jul 28, 2018 at 06:54 AM, Gudjon Gudjonsson wrote:

I don't need accuracy, just stability. I do have a frequency source
that I can use to tune into the frequency I'm after
but then I would like to keep this stable.

If your 7L13 is anything like my 7L12, it should have a 'phase lock' switch which locks the 1st LO to a multiple of some frequency (about 700kHz, I think) for spans of less than 200kHz/div. This works well on mine, but the little slide switch that engages phase lock mode did need a squirt of DeoxIT D5 before it worked reliably.

This alone should give you the stability you need, after 20 minutes or so of warmup.

Chris

Hi again

Now I have done quite a few measurements with my 7L13. I just used a
know frequency source to tune it into the frequency I am searching for
and then I do the measurement. This works well enough for my zero span
measurements with resolution of 300kHz.

I did buy a frequency meter for up to 5.8GHz and tried to correlate
the frequency of the YIG oscillator with the voltage between pin 6 of
U2110 and ground with a more precise voltage measurement than the
frequency readout contains.

Regarding phase locking of LO1. According to the manual, the span is
done in the following way:

= 5MHz/div: Main coil of the YIG

2MHz/div to 100kHz/div: FM-coil
<=50kHz/div: The phase lock loop of LO2, and then the LO1 can be phase locked.

I found out that the plugin need through calibration since the center
frequency moves quite a lot with changing span.

But the nice thing is that I think I have solved the EMC problem the
setup was supposed to help solving and my 7L13 is very helpful in my
EMC precompliance toolset.

Regards
Gudjon

/g/TekScopes/album?id=86278


-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Gudjon Gudjonsson
Enviado el: domingo, 19 de agosto de 2018 21:28
Para: TekScopes
Asunto: Re: [TekScopes] 7L13, more exact frequency readout

Hi again

Now I have done quite a few measurements with my 7L13. I just used a know frequency source to tune it into the frequency I am searching for and then I do the measurement. This works well enough for my zero span measurements with resolution of 300kHz.

I did buy a frequency meter for up to 5.8GHz and tried to correlate the frequency of the YIG oscillator with the voltage between pin 6 of
U2110 and ground with a more precise voltage measurement than the frequency readout contains.

Regarding phase locking of LO1. According to the manual, the span is done in the following way:

= 5MHz/div: Main coil of the YIG

2MHz/div to 100kHz/div: FM-coil
<=50kHz/div: The phase lock loop of LO2, and then the LO1 can be phase locked.

I found out that the plugin need through calibration since the center frequency moves quite a lot with changing span.

But the nice thing is that I think I have solved the EMC problem the setup was supposed to help solving and my 7L13 is very helpful in my EMC precompliance toolset.

Regards
Gudjon