Topics

FT8 checking my signal


Radioman ZeroZero
 

FT8 screenshot of my own transmission taken 1 band down whilst transmitting on 20m.  Its a good way to check your not over modulating!
--
Thanks Steve M0ZEH


jdow
 

What are you using as a transmitter? You may have discovered a bug in your Transmitter.
{^_^}

On 20210311 06:57:28, Radioman ZeroZero wrote:
FT8 screenshot of my own transmission taken 1 band down whilst transmitting on 20m.  Its a good way to check your not over modulating!
--
Thanks Steve M0ZEH
Screenshot-2021-03-11-144506.jpeg


Dave Cole
 

How many db down are the spurs I see on each side? I can't make out the scale.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 3/11/21 9:18 AM, jdow wrote:
What are you using as a transmitter? You may have discovered a bug in your Transmitter.
{^_^}
On 20210311 06:57:28, Radioman ZeroZero wrote:
FT8 screenshot of my own transmission taken 1 band down whilst transmitting on 20m.  Its a good way to check your not over modulating!
--
Thanks Steve M0ZEH
Screenshot-2021-03-11-144506.jpeg


jdow
 

More to the point, how strong is the desired signal on 20 meters? The receiver could be completely overloaded. But he'd know to check that, right?

{^_-}

On 20210311 09:21:53, Dave Cole wrote:
How many db down are the spurs I see on each side?  I can't make out the scale.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 3/11/21 9:18 AM, jdow wrote:
What are you using as a transmitter? You may have discovered a bug in your Transmitter.
{^_^}

On 20210311 06:57:28, Radioman ZeroZero wrote:
FT8 screenshot of my own transmission taken 1 band down whilst transmitting on 20m.  Its a good way to check your not over modulating!
-- 
Thanks Steve M0ZEH
Screenshot-2021-03-11-144506.jpeg









Radioman ZeroZero
 

Hi Jdow,

Can I damage my RX-888 receiver with indoor loop?  It is very overloaded when on the signal.

The transmitter is on another outdoor antenna with ICOM IC-746.
--
Thanks Steve M0ZEH


Radioman ZeroZero
 
Edited

Dave,

I think the spurs are noise.
--
Thanks Steve M0ZEH


Mag loop Simon
 

I do hope thats not your signal!

Not on 1/2 frequency..

As a matter of interest whats the rig? ( ask cos if has 2 antenna sockets and rx out you could use the 888 as a panadapter on the loop too.)

Simon g0zen


jdow
 

Probably. Usual protection is at static discharge energy levels. At one time I had a Gap Titan vertical and my long wire. The Gap Titan could generate volt level signals when I was transmitting at 100 watts on my Pro-II. That may cause damage long term. Although it is just a little above the power used in diode double balanced mixers as the LO. Regardless, with an abundance of caution I draw a mental the line at about 20 mW or 1 Vrms.

Of the receiver is very overloaded on frequency it will generate all manner of strange results. Put in some attenuation until the front end is not overloaded. Then look. Note that the RX-888 is wide open on the front end with no prefiltering to speak of beyond anti-aliasing filters appropriate to its native sample rate.

{^_^}

On 20210312 08:15:15, Radioman ZeroZero wrote:
Hi Jdow,

Can I damage my RX-888 receiver with indoor loop?  It is very overloaded when on the signal.

The transmitter is on another outdoor antenna with ICOM IC-746.
--
Thanks Steve M0ZEH


Radioman ZeroZero
 

As I mainly want to use the sdr as a panadaptor it sounds like I need to short the antenna input on the sdr when I transmit on the IC-746 to avoid any damage to the sdr fornt end.
--
Thanks Steve M0ZEH


jdow
 

Where is the SDR patched into your setup. Are you using it as an IF spectrum device or are you using it as if it was a separate device on your antenna. If it is tapped off the transceiver's first IF then you should be safe. If you are on an RF output designed for a second receiver it is probably OK. If it is on the antenna used for transmit, a really high quality RF relay that disconnects and shorts the receiver input when transmitting is called for.

{^_^}

On 20210313 03:36:14, Radioman ZeroZero wrote:
As I mainly want to use the sdr as a panadaptor it sounds like I need to short the antenna input on the sdr when I transmit on the IC-746 to avoid any damage to the sdr fornt end.
--
Thanks Steve M0ZEH


Radioman ZeroZero
 

The sdr setup is independent of the transmitter.  The transmitter and associated outdoor antenna is separate to the sdr receiver and indoor loop.  It turns out my solution could be simple, a couple of diodes across the sdr antenna input.  See here http://www.kk5jy.net/rf-clipper/  Although I won't be able to see my transmission if I do I can use a temporary attenuator as you suggested earlier.  At least the sdr should be protected and I should be able to use the sdr as a pan adaptor.
--
Thanks Steve M0ZEH


Mag loop Simon
 

What trx rig radio are you using?
Cos doing the way you want to kinda sucks..
There are much better ways to do it..

Depending upon trx rig.( main rig.)

G0zen


jdow
 

The diode fix would be good if you do not have nearby high power transmitters. If you do have nearby high power transmitters "diodes do as diodes are." They can cause IMD problems on overload.

And, on this you can probably trust me thoroughly. We are talking about minimum signals well beneath one microvolt, -107 dBm. We are dealing with transmitters perhaps +50 dBm. That's nearly 150 dB of attenuation before your signal reception at your site will become unsuited for what you want. You have no idea how hard it is to get an honest 100 dB in a screen room within a screened facility (floating on a bed of mercury.) (That's the old Rockwell International calibration lab in their Anaheim campus.) We designed for 120 dB isolation between input and output of the GPS satellite frequency synthesizer. We figured we could "fudge" and make 80 dB just about work to bury the oscillator's version of 10.23 MHz in the noise sidebands from the oscillator. We managed 100 dB. This is on Phase IIa. On the next satellite set built they tried to take out some of the ceramic PCB to hogged out alumin(i)um box grounding wires. They could not take out even one of them and maintain enough isolation. This is with a solid lump of aluminum with a +/- 2 Hz synthesizer in about 2 micro Hz steps on the output and a stable but maybe off frequency Cs standard. (They actually did end up using that synthesized that way. It was designed to corrupt the GPS signal "so the soviets could not plunk a nuke down Jimmy Carter's toity" ((C) jdow) using our GPS.)

Betcha you can hear yourself on 20 meters just fine. You may hear yourself too well as a matter of fact.

{^_-}  (I had "a attitude" in those days. I think most of it is still here, too. {o.o})

On 20210313 04:09:56, Radioman ZeroZero wrote:
The sdr setup is independent of the transmitter.  The transmitter and associated outdoor antenna is separate to the sdr receiver and indoor loop.  It turns out my solution could be simple, a couple of diodes across the sdr antenna input.  See here http://www.kk5jy.net/rf-clipper/  Although I won't be able to see my transmission if I do I can use a temporary attenuator as you suggested earlier.  At least the sdr should be protected and I should be able to use the sdr as a pan adaptor.
--
Thanks Steve M0ZEH


jdow
 

746, I believe. I don't have a manual for it to check the schematic. If you do, chime in if it has a monitor receiver output.

{^_^}

On 20210313 04:45:33, Mag loop Simon wrote:
What trx rig radio are you using?
Cos doing the way you want to kinda sucks..
There are much better ways to do it..

Depending upon trx rig.( main rig.)

G0zen 






Radioman ZeroZero
 

I'm transmitting at 100W on the IC-746 and no it doesn't have a monitor.  As I don't need to monitor the sdr when I'm transmitting I thought my idea would work. i.e. it will clamp the sdr input when I'm transmitting.
--
Thanks Steve M0ZEH


Roger Shaltry
 

Let me save you some money and grief.  I used my Perseus as a external receiver on my Elecraft K3.  There is a port dedicated to this use.  Worked for a few days and then blew out a $1000 radio.
Talked to Elecraft and they said that there is a pin diode switch involved with the external receiver port.  This seems to be common technology  That runs on 5 VDC.  When it switches it produces a pulse that will eventually destroy your SDR radio.
I ended up building a protection circuit for use on all of my SDR radios.  This has worked very well even with a nearby lightning strike (near field coupling) that blew out all of my USB connected equipment including the computer ports.  Never blew a protection circuit or the front end of any SDR radio.
Here is another solution (a lot less expensive then a new radio) buy a (about $40) Advanced Receiver Research preamp (HF or what ever you need) and use it ahead of you other SDR equipment.  I had lightning blow one of these preamps until I built my protection circuit for use ahead of all SDR equipment and preamp.  I have a 4x1 commercial splitter now and I use the protection device ahead of the splitter maybe followed by a preamp.
I may be able to locate the schematic and post it.


jdow
 

With separate antennas it will certainly "work" during transmit. During receive a ham or broadcast station nearby could place a high enough signal level on the input to cause overload problems. HOWEVER, if the antenna used is moderate to high efficiency you can insert an attenuator on the input with little or no degradation on SNR to your ears or digital audio decoders such as PSK-31.

{^_^}

On 20210313 06:16:35, Radioman ZeroZero wrote:
I'm transmitting at 100W on the IC-746 and no it doesn't have a monitor.  As I don't need to monitor the sdr when I'm transmitting I thought my idea would work. i.e. it will clamp the sdr input when I'm transmitting.
--
Thanks Steve M0ZEH


Radioman ZeroZero
 
Edited

I built the sdr input protection device and it works as expected.  Now when I transmit on my other radio the sdr's front end is protected.  Well worth the £1 worth of diodes.
--
Thanks Steve M0ZEH


 

Circuit and Diode type and model would help me understand how it is working. The picture is not speaking a thousand words unfortunately :-)

73 de k1jbd
bammi


Bill Walch
 

Bammi,

The original photo shows two Schlocky Diodes (1N5817) in opposite polarities, forming a bi-directional clamp. This is illustrated in the diagram (c) below. The major difference between a typical signal diode (rectifier) is that a Schlocky Diode is extremely fast switching, in the order of uS. You can see datasheet for the 1N5817/8/9 HERE. This diode is rated at 10A maximum Forward rms current. How that relates to induced RF, is unknown to me. However, I would assume that if the Tx and Rx antennas are separated at some distance, the amount of RF energy seen at this clamp should be low enough to prevent damage to the diodes, again, speculation on my part. Hope this helps.

73's, Bill




On 4/4/2021 5:57 PM, bammi via groups.io wrote:
Circuit and Diode type and model would help me understand how it is working. The picture is not speaking a thousand words unfortunately :-)

73 de k1jbd
bammi