low rx sensitivity - caused by miswound toroids?

General discussion and support for the Peaberry SDR V2.

low rx sensitivity - caused by miswound toroids?

Postby k7kw » Thu Jul 03, 2014 10:31 pm

Hello. My v2 suffers from low receive sensitivity: about 20dbm below what I expect to read, and I'm hearing only very strong signals. No transmit as far as I can tell. 20m and 40m have the same problems. Others not tested.
I know now that I should have observed direction when winding the toroids, but I probably did not. Is low signal strength a possible result of this error?
thanks a lot'
Doug
k7kw
 
Posts: 19
Joined: Fri Oct 18, 2013 3:22 pm

Re: low rx sensitivity - caused by miswound toroids?

Postby AE9RB » Thu Jul 03, 2014 11:54 pm

Everyone who has complained about sensitivity has found soldering errors. Sounds like you can eliminate problems with the digital logic at least.
73 David AE9RB
AE9RB
Site Admin
 
Posts: 511
Joined: Thu Nov 15, 2012 5:27 am
Location: Portland, Oregon, USA (CN85ql)

Re: low rx sensitivity - caused by miswound toroids?

Postby k7kw » Wed Jul 09, 2014 9:25 pm

OK, so I've checked about all the joints with an ohmmeter; nothing found. Here are two more symptoms:

1 - there is no measurable power on transmit, although the spectrum scope shows my audio ok
2 - the relay is definitely not clicking when I change bands

Anyone interested in taking a look at it (as in, I put it in your hands)?

thanks
Doug
k7kw
 
Posts: 19
Joined: Fri Oct 18, 2013 3:22 pm

Re: low rx sensitivity - caused by miswound toroids?

Postby W4MMP » Thu Jul 10, 2014 1:11 am

Hi,
Is the LED blinking on transmit? As for the relay, what is the voltage level at the anode of D3. It should toggle between approx. 5V and 0V depending on band.
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Re: low rx sensitivity - caused by miswound toroids?

Postby k7kw » Thu Jul 10, 2014 4:44 pm

Thanks, Ron
Yes, the led blinks fast on transmit, and I can hear the signal on my test equipment, but the power level is too low to measure.
The anode of the diode is high (+5) on 20 & 30 mtrs, low (~0) on 40 & 60 mtrs. I suppose the relay may just be to quiet for me to hear.
On receive, I can hear and see a 0dBm (actual) signal, but when I dial the s-meter to full sensitivity ((a 0dBm (actual) signal shows +40dBm (measured))), then no signal (actual) drops to just +30dBm (measured). I cannot hear a -73dBm (actual) signal (should be s9 measured); so my receiver front end seems to be attenuated somewhere.
Doug
k7kw
 
Posts: 19
Joined: Fri Oct 18, 2013 3:22 pm

Re: low rx sensitivity - caused by miswound toroids?

Postby k7kw » Thu Jul 10, 2014 4:46 pm

I tested on all 4 bands.
Doug
k7kw
 
Posts: 19
Joined: Fri Oct 18, 2013 3:22 pm

Re: low rx sensitivity - caused by miswound toroids?

Postby AE9RB » Thu Jul 10, 2014 4:59 pm

When the signal is attenuated with a short to ground or the path is open you will be unable to isolate the problem with a multimeter. You must use a signal generator and oscilloscope. Even then it can be tricky. The other option is to rework connections and magnetics until you stumble upon the part with problems.

Try replacing T1.
73 David AE9RB
AE9RB
Site Admin
 
Posts: 511
Joined: Thu Nov 15, 2012 5:27 am
Location: Portland, Oregon, USA (CN85ql)

Re: low rx sensitivity - caused by miswound toroids?

Postby kz1x » Thu Jul 10, 2014 5:34 pm

Yup, sounds like T1 is either miswound or installed 90 degrees off.
kz1x
 
Posts: 232
Joined: Wed Aug 07, 2013 1:28 am

Re: low rx sensitivity - caused by miswound toroids?

Postby k7kw » Thu Jul 10, 2014 7:43 pm

I rewound and re-installed T1 with no change in result.
Doug
k7kw
 
Posts: 19
Joined: Fri Oct 18, 2013 3:22 pm

Re: low rx sensitivity - caused by miswound toroids?

Postby W4MMP » Thu Jul 10, 2014 8:06 pm

Hi,
It really appears that something in the ANT path is shorted to ground. If none of the bands are working, I would look beyond the BPF section for something amiss.

Or (a thought just occurred to me) check the state of RX, it toggles between ~5V and ~0V for transmit/receive.. At the moment I can't remember which is which for the toggle action. The point is, make sure it is toggling.
73
Ron / W4MMP
W4MMP
 
Posts: 579
Joined: Fri Jan 03, 2014 3:31 pm
Location: Lovettsville, Virginia FM19EG

Next

Return to Peaberry SDR V2

Who is online

Users browsing this forum: Bing [Bot] and 1 guest

cron