[Lowfer] Problems with receiving loop system

[Laurence KL7 L]

I  seem to remember common mode node issues with the loop amp design - it was quite a high gain amp and the varactors worked fine but picked up sheds of noise from the feeder line - its been a few years and a little gray. Results were poor s/ns

Laurence

Sent from my iPhone

> On Nov 1, 2019, at 3:37 PM, "jrusgrove at comcast.net" <jrusgrove at comcast.net> wrote:
> 
> Zack
> 
> Step one would be to measure the FET source, gate and drain dc voltages and the transistor emitter, base and collector dc voltages to verify that all is well with the active devices. Also, you may want to verify the varactor voltage at the diode side of the 1.5M resistor. If you're not sure what the voltages should be you could report them here.  
> 
> Jay W1VD  
> 
> 
> ----- Original Message -----
> From: Zack Widup <w9sz.zack at gmail.com>
> Reply-To: Discussion of the Lowfer (US, European, & UK) and MedFer bands <lowfer at mailman.qth.net>
> To: Discussion of the Lowfer (US, European, &amp, UK) and MedFer bands <lowfer at mailman.qth.net>
> Sent: 11/1/2019 5:47:12 PM
> Subject: [Lowfer] Problems with receiving loop system
> ________________________________________________________________________________
> 
> I tried sending this but had an attachment that was too big, so it may not
> have gone through. Please excuse if it did.
> 
> I may have mentioned the problems I have had a while back, but I wanted to
> mention it again as the lowfer season for this year is about to start or is
> underway already.
> 
> I built a 20 turn rectangular loop 5 feet on a side on pvc tubing. The
> turns are spaced about an inch and a half apart. I placed taps at 3, 5, 10,
> 15 and 20 turns so I could select smaller numbers of turns.
> 
> I built the K0LR high-gain preamp. I am attaching the pdf file of this but
> not sure if the group allows attachments. But you may be familiar with it.
> See the second schematic with the MVAM109 diodes. My loop is about 100 feet
> from the shack and I have 100 feet of supply and tuning voltage cable and
> RG-58 coax cable running to a box at the base of the loop which has the
> preamp and tuning circuit in it. Just to make sure everything was getting
> proper connections, I put a 50 ohm termination at the loop end of the coax
> and measured 50.5 ohms at the other end in the shack. The power wire is
> supplying voltage measured at 12 volts to the preamp box, reduced with a
> voltage regulator to 9 volts inside the preamp box the circuit. I am using
> MVAM109 diodes, and the tuning voltage at the loop end can be varied from 0
> to 9 volts, as it should be. I also included the W1TAG loop ATU circuit,
> which allows me to add more capacitances in parallel with the tuning diodes
> to cover a wider range, switched with reed relays.
> 
> After all of this, I am very disappointed in the loop system performance. I
> don't know what I did wrong. I have tried both my TS850S (with the LF
> attenuator circuit removed) and a Softrock Ensemble II LF version as
> receivers. The loop system seems to do OK receiving AM broadcast signals on
> both receivers. However, I cannot receive anything below the broadcast
> band. I cannot receive a local NDB on 407 kHz (CMI) at all with the loop.
> 
> I connected my MFJ vertical that is designed for 40 through 10 meters to
> the TS-850 and to the Ensemble II and they both actually receive AM signals
> with that antenna better than the loop system, as well as a CW station on
> 475 KHz, the local NDB signal on 407 kHz and several other NDB signals. It
> appears that the waterfall of the SDR receiver shows a lot more noise
> received from the loop but actual signal strengths across the AM band are
> weaker and nonexistent below that.
> 
> I also want to try an E-probe antenna, but I wish I knew what thr trouble
> with the loop system is. Any suggestions would be appreciated.
> 
> 73, Zack W9SZ
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