Output transmit garbled

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Output transmit garbled

Postby kd5kll » Sun Apr 05, 2015 11:03 pm

The transmit of the radio is garbled.

When I try USB into the dummy load and listen to it on my shortwave radio, the audio sounds garbled, almost as if it is being over driven.

When I try CW and key the transmitter, I hear the tone, but I also hear a loud buzz.

Same with FM, I hear the carrier tone and a loud buzz.

I don't have a oscilloscope yet (it's on order and on it's way). Is there anything I can check now, or do I need to wait for the scope?
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Re: Output transmit garbled

Postby pilotcfii » Mon Apr 06, 2015 2:15 am

There are much more knowledgeable guys on here than me, but it is quite possible that at even one watt you are overdriving your receiver.

The second possibility is that you are producing more than 1 watt and your PA is non-linear in that region. You don't say if you are monitoring the power out, but if not I recommend that you do and ensure you don't exceed the 1 watt limit. My PB can output 2 and more watts so I have to reduce the drive to keep within 1 watt. You can reduce power using the Power slider that appears during Tx in HPSDR.

If this doesn't help, I'm sure one of the other PB users on this forum can help. Good Luck
73
Dan Malcolm
K4SHQ CFI/II
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Re: Output transmit garbled

Postby kz1x » Mon Apr 06, 2015 2:51 am

What are you using for a power supply?
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Re: Output transmit garbled

Postby AE9RB » Mon Apr 06, 2015 3:12 am

pilotcfii wrote:it is quite possible that at even one watt you are overdriving your receiver.

This. It's unlikely your SW radio can handle S9+100 (yes, 100, not a typo). The AGC is probably going bonkers.
73 David AE9RB
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Re: Output transmit garbled

Postby kz1x » Mon Apr 06, 2015 1:55 pm

I don't doubt a possible overload condition either, but, he's transmitting a watt-or-so (+30 dBm) into a dummy load and using a nearby receiver (saturates at -40).

Any reasonable hardware setup would yield enough attenuation in this case to not fully toast the RX front end. 50 dB from the load and 20 from path are conservative numbers, you'll no doubt agree.

Exceptions could include using the same power supply for both radios and having some anomalous coupling there.

TX noise on the Peaberry, when listened to locally, is almost always either a buzzy power supply and/or some PC generated artifact.
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Re: Output transmit garbled

Postby kd5kll » Mon Apr 06, 2015 2:08 pm

kz1x wrote:What are you using for a power supply?


13.8VDC 1A wall wart.
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Re: Output transmit garbled

Postby ks1h » Mon Apr 06, 2015 2:28 pm

Also beware of RF hash from the Peaberry getting into your receiver. I am having a buzz too but have come to the conclusion most of it doesn't have anything to do with the transmitted signal. If you want to have some fun download a copy of Spectrum Lab (see April QST article on measuring frequencies) so that you can get a spectrum of the audio that is coming out of your station receiver. Run your Peaberry into the dummy load and disconnect any antenna from your receiver and see what you get. In my case I got quite a lot and it didn't change with tuning the receiver!. Then connect an inch or two of antenna to your receiver and repeat. You should see some additional lines that represent the transmitted signal leaking out of the Peaberry. These will change frequency as you tune the receiver. In my case there is the main carrier but then also some curious 120Hz sidebands. Not sure what these are from yet but bottom line is my "buzz" doesn't seem to be present in the transmitted signal.

73, Ken KS1H
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Re: Output transmit garbled

Postby kd5kll » Mon Apr 06, 2015 3:52 pm

ks1h wrote:Also beware of RF hash from the Peaberry getting into your receiver.


I'm not seeing a lot of RF hash on receive. In fact, this is a really clean and sensitive receiver. The only noise I get on receive comes from my plasma TV (wife is already speccing out a new LCD tv to replace it), and from a couple of noisy little netgear switches. I hear the same noise on my shortwave radio, so I don't think the peaberry is adding any RF hash. Audio on SSB and AM broadcasters is clean and clear with no buzz or distortion. I have a 20M dipole in the attic now, and I on JT65 I've received five continents so far, so I think the receiver is working fine.

I just called CQ on JT65 on 20M, and pskreporter showed quite a few receives all over the continental US and southern Canada. So, I think I'm worrying over nothing. It just seems like I'm having trouble with making QSOs. But at 1W, I may just need to practice more patience...
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Re: Output transmit garbled

Postby kz1x » Mon Apr 06, 2015 3:53 pm

kd5kll wrote:
kz1x wrote:What are you using for a power supply?


13.8VDC 1A wall wart.


Thanks. I suspected that this might be an issue.

While there are a few wall warts that do work in this service, I have tried 21 different ones here out of curiosity and only two worked, and even those, not great. I find the ratings on even Jameco sourced supplies for this purpose to be overly enthusiastic.

The only one that's been universally perfect is this purpose-built unit:

https://proaudioeng.com/products/pae-kx33-ac-power-supply/

The nature of this kit radio is that it appeals to a large group of newer hams, many of whom do not have 'traditional' test benches with current-rich power supplies and the like. That's one reason this anomaly crops up from time to time, more often on the PB radios than others.

I assume you do not have an oscilloscope to view what that wall wart output looks like when the PB is transmitting ...

Do you have an alternate low impedance power source, like a small gel cel, bench test supply, or other power supply for the PB?
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Re: Output transmit garbled

Postby kd5kll » Mon Apr 06, 2015 8:15 pm

kz1x wrote:The only one that's been universally perfect is this purpose-built unit:

https://proaudioeng.com/products/pae-kx33-ac-power-supply/


Ouch! $60 for a power supply?

kz1x wrote:I assume you do not have an oscilloscope to view what that wall wart output looks like when the PB is transmitting ...


Not yet, but I have an oscilloscope ordered and on the way.

kz1x wrote:Do you have an alternate low impedance power source, like a small gel cel, bench test supply, or other power supply for the PB?


No, I've been looking at getting a bench test supply. I have to wait for next month's allowance. I've spent this month's allowance on the scope! :D
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