RX Level Calibration

User avatar
KC4LZN
Posts: 32
Joined: Fri Oct 09, 2020 2:23 pm

RX Level Calibration

Postby KC4LZN » Wed Jan 27, 2021 3:46 pm

I noted the other day, when I had my rig (7000DLE MKII) connected to a dummy load, tuned to the 40m band, I had an S5 level of noise. I went to all of the other bands and the S level was 0.

Is there something that I should've done on receipt of this rig to ensure all bands were receiving properly and to the S Level they should be presenting?

I looked in the Thetis 1.1 Manual and there is a reference to Level Cal but not sure if that is what it is referring to and also points to a signal generator also and I'm guessing, injecting say a 1 kHZ signal into the antenna port for calibration.

Just not enough information for me to go on and sure don't want to mess something up but clearly, something is wrong with the high noise level on 40 meters.

My apologies as well, if this is the wrong subject group but was the closest I could find to what I'm dealing with.

73
John
KC4LZN
NC3Z
Posts: 464
Joined: Sun Oct 29, 2017 8:57 pm
Location: Merritt, NC

Re: RX Level Calibration

Postby NC3Z » Wed Jan 27, 2021 3:54 pm

KC4LZN wrote:I looked in the Thetis 1.1 Manual and there is a reference to Level Cal but not sure if that is what it is referring to and also points to a signal generator also and I'm guessing, injecting say a 1 kHZ signal into the antenna port for calibration.


It's covered elsewhere in the forum I believe, but to do a cal you inject a signal with a signal gen at the freq and level you have selected under General > Calibration > Level Cal.

So if you use a the default of 10Mhz and -73dbm you inject a signal at 10MHz @ -73dBm and then hit the Start button.
Gary NC3Z
User avatar
KC4LZN
Posts: 32
Joined: Fri Oct 09, 2020 2:23 pm

Re: RX Level Calibration

Postby KC4LZN » Wed Jan 27, 2021 8:36 pm

Thanks, Gary. I'll take a closer look at the procedures and go from there, then report back the outcome.

73
John
KC4LZN
NC3Z
Posts: 464
Joined: Sun Oct 29, 2017 8:57 pm
Location: Merritt, NC

Re: RX Level Calibration

Postby NC3Z » Wed Jan 27, 2021 8:40 pm

You will also find many posts about using 500Hz filter to check the signal level on the S meter per ITU standards.
Gary NC3Z
User avatar
KA1GXR
Posts: 40
Joined: Sun Apr 09, 2017 10:53 pm
Location: ASHLAND MA

Re: RX Level Calibration

Postby KA1GXR » Wed Jan 27, 2021 10:57 pm

Make sure each band is in same mode and bandwidth or levels will vary . Ideally test in cw mode narrow bandwidth like 500hz or narrower as suggested . There are some power supply birdies in different Anan models causing noise at various points in some bands. Most noticed in dummy load.
Are you using a switching power supply or linear? They can be noiser on different bands
I would not try a cal without calibrated signal generator .

Enjoy your Radio
Tom
KA1GXR
User avatar
w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: RX Level Calibration

Postby w-u-2-o » Wed Jan 27, 2021 11:22 pm

Try a fresh database in case the default 40m calibration value has somehow become corrupt.
User avatar
KC4LZN
Posts: 32
Joined: Fri Oct 09, 2020 2:23 pm

Re: RX Level Calibration

Postby KC4LZN » Thu Jan 28, 2021 12:28 am

I will attempt the database from a fresh perspective first. Beyond that, I will have to acquire a well regulated, calibrated signal generator if the default calibration standard replacement proves no change.

The power supply is a switching supply from Samlex Model 1235. The signal is being seen from both the connected dummy load and also with no dummy load connected. I have not conducted but will power the radio with a battery to rule out the power supply.

Appreciate the input and will let you know how it goes. I will perform the replacement database after this storm moves through Central Florida first.

73
John
User avatar
w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: RX Level Calibration

Postby w-u-2-o » Thu Jan 28, 2021 12:57 am

An S5 birdie from a power supply or elsewhere will be plainly evident in the spectral display. If there isn't any in your receive passband you don't need to play games with going to battery power.
User avatar
KC4LZN
Posts: 32
Joined: Fri Oct 09, 2020 2:23 pm

Re: RX Level Calibration

Postby KC4LZN » Thu Jan 28, 2021 9:34 am

Didn't even get that far with the battery.

Guess I'll never understand Gremlins. Reset the database and levels were back to normal. S Meter doesn't show that S5 level noise any more.

Thanks for the tips and off to work on re-building this database.

73
John
User avatar
w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: RX Level Calibration

Postby w-u-2-o » Thu Jan 28, 2021 12:26 pm

Great news!

IMHO it is worth going through the level cal exercise. Most who have done it have found they were off about 1 S-unit, myself included. But you do need a legit calibration signal generator source with a trusted output level. I used the 10MHz output of my GPS DO padded down to -30dBm and confirmed by an HP spectrum analyzer.
K9RX
Posts: 414
Joined: Fri Apr 14, 2017 3:47 pm

Re: RX Level Calibration

Postby K9RX » Thu Jan 28, 2021 1:32 pm

I will take a guess as to what you are seeing: you have some level of ATT selected on 40M! Just set it to 0 and you'll be back where you 'need' to be. Nothing else needed.

Gary
K9RX

this assumes your natural noise level is at that level ... in which case it is a moot point.
User avatar
w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: RX Level Calibration

Postby w-u-2-o » Thu Jan 28, 2021 5:55 pm

It was a bad database, Gary...
User avatar
KC4LZN
Posts: 32
Joined: Fri Oct 09, 2020 2:23 pm

Re: RX Level Calibration

Postby KC4LZN » Thu Jan 28, 2021 6:02 pm

I agree, Scott. One, it will let me better understand the process of the level calibration with this rig and two, it will ensure that the S meter is where it should be. I will have to probe the locals for a good, calibrated signal generator.

73
John
K9RX
Posts: 414
Joined: Fri Apr 14, 2017 3:47 pm

Re: RX Level Calibration

Postby K9RX » Fri Jan 29, 2021 3:54 pm

Well keep it in mind John, Unfortunately since resetting the DB would also set the ATT to 0 we don't know! .... the fact that only one band was showing it says you might have turned it on and forgot about it ...

just a thought.

g.
K9RX
Posts: 414
Joined: Fri Apr 14, 2017 3:47 pm

Re: RX Level Calibration

Postby K9RX » Fri Jan 29, 2021 3:58 pm

PS: re calibration. The out of the box performance is extremely good and unless you're using the radio to do absolute measurements calibration isn't strictly necessary. I checked it as I had a source (Elecraft XG3) and if I recall it was off by 1 db at S9. Note that is the only thing that you calibrate, the scaling is done digitally and is indeed dead on.

Gary
K9RX
NC3Z
Posts: 464
Joined: Sun Oct 29, 2017 8:57 pm
Location: Merritt, NC

Re: RX Level Calibration

Postby NC3Z » Fri Jan 29, 2021 4:20 pm

K9RX wrote:The out of the box performance is extremely good


I have to agree, I am using a Rhode & Schwarz sig gen and my 7000 is within 1dB with a default DB. So if you do not have a highly accurate source I would not worry about it.

Now a freq cal is another matter, but all you need is to be able to hear WWV
Gary NC3Z
User avatar
w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: RX Level Calibration

Postby w-u-2-o » Fri Jan 29, 2021 5:54 pm

Mine was off by 6dB
User avatar
KA5KKT
Posts: 129
Joined: Thu Aug 06, 2020 6:51 pm

Re: RX Level Calibration

Postby KA5KKT » Sat Jan 30, 2021 5:53 pm

While on the topic of RX Level Calibration...

Using a non-Anan radio at present (7000 on the way soon), I find that in calibrating with a single frequency signal source for S-9, then switching to SSB signals, there is a dispariity. It has been suggested that the disparity is due to the wideband reception of +/- 3kHz. For instance, under SSB I show an S-7 or so noise level (40 meters) while the waterfall shows S-3 or 4. By the sound of it, it isn't really near that high as S-7.

I suppose one could calibrate with a wide band singnal (white noise?) generator or something that would be better suited for SSB signals. The output level of the inexpensive wide band generatiors I have seen to vary with frequency. Thus the generator would need to be calibrate the generator before using such to calibrate for SSB.

Are there some thoughts to be shared on calibrating for a wide signal of variable frequencies such as SSB..?


Kind regards,
Dick - KA5KKT
User avatar
w-u-2-o
Posts: 5540
Joined: Fri Mar 10, 2017 1:47 pm

Re: RX Level Calibration

Postby w-u-2-o » Sat Jan 30, 2021 6:34 pm

Dick,

Please read this topic, and perhaps also the references contained within. This will explain why you see the results you see.

https://apache-labs.com/community/viewtopic.php?f=6&t=2463

73,

Scott
User avatar
KA5KKT
Posts: 129
Joined: Thu Aug 06, 2020 6:51 pm

Re: RX Level Calibration

Postby KA5KKT » Sun Jan 31, 2021 2:38 pm

Thanks, Scott.

Return to “Thetis”