SWR and Receive

Dwayne_AB6A

I love the radio and multilink but running into some antenna issues... A G5RV and SWR appears to be as important for receive as it is for transmit... When slices are separated far enough, the receive slice that does not match my antenna tuner has significant signal degradation. Has anyone else observed this and any feedback on how to mitigate??

Bill -VA3WTB

I guess your antenna needs to be more broadbanded then it is. Your listening to a portion of the band that your antenna can't work proplerly on.

Dwayne_AB6A

Makes perfect sense... I'm still learning and up until now thought that SWR/bandwidth really only affected transmit.

Bill -VA3WTB

No,,, try this,,it helps you see what is going on.
Zoom way out so you see the full band, look at the noise floor. You will see a spot were the floor is high and down the band it may be much lower. Manually tune your tuner and you can see the floor move up and down depending were your antenna is resenant

Rick - W5FCX

Have a look at zs6bkw, optimized variant of g5rv that often doesn’t require a tuner. https://www.w5ddl.org/files/Zs6bkw_vs_G5rv_20100221b.pdf

Dwayne_AB6A

Thanks all! Im the primary user of my radio and my current antenna choices are limited due to my property/location. I see a vertical in my future.

N8AUM

Pretty sure the ATU is out of the picture on the receiver? I spent a whole day measuring some of my radio's receiver input impedances with one of my VNA's and not too many radios are 50 ohms or even close, lots of variables, preamp on or off, attenuation just to name a few. 
 

Bill -VA3WTB

What are the primary bands do you use. I use 40m and 80m most the time. My city lot is small. I have a 50 foot tower. I am using a 40 and 80 meter dipole that is 63 feet over all end to end. The SWR hardly changes at all from the top of the band to bottom.

Tim N9PUZ

All of your antenna system losses whether they be due to SWR, feedline loss, or a mismatch will effect both transmit and receive.

N8AUM

I think Dwayne's question was regarding the ATU with the radio while receiving. As far as I know the ATU is not in play when receiving. I've done some mods with older radios  that let me switch on the ATU for both xmit & receive and most of the time the signal was weaker because the ATU was matching the antenna system to get the lowest SWR to satisfy the transmitter. An easy test is to use an outboard tuner and I'll bet if after tuning for best SWR in transmit than if you tune for maximum receive signal the settings will not me the same on the tuner. 

Dwayne_AB6A

Just to be clear - I am using an external ATU so radios ATU is in bypass for all bands. I have a Palstar HF-Auto.

The question is more around how big a difference a tuner plays for both transmit and receive... Not just transmit.

Since antenna tuning makes such a difference for receive, how should antennas be configured for optimal multi user configuration?

For each user, you can’t tell what band they are using or how the antenna is tuned irrespective of internal or external ATU.

Dwayne_AB6A

I have issues with height and space and am even considering a mag loop which now I believe would exacerbate my issues.

John Swink

Try a magnetic loop antenna.  I use a no tune magnet loop with 30 dB preamp connected to the RXA port on my 6600.  It is only 38" in diameter and is mounted on a 10 foot high post and works great on 160 - 30 meters.  I bought mine several years ago from Pixel.  I believe it is now sold by DX Engineering.  While not cheap, it is compact and pulls out the really weak signals.

HCampbell WB4IVF

On receive, engaging an ATU to lower SWR will not increase signal to noise ratio (SNR) and therefore signal intelligibility on the HF bands.  Yes, the signal will appear “louder”, but so will the noise (remember that noise is signal too), and the net result is no change in SNR.

What can make a major difference on receive is the use of directional antennas, which reduce noise from directions other than the desired signals, and therefore may increase the SNR.  That’s how specialized “receive” antennas like beverages work.  They have negative gain in all directions, but reject noise from undesired directions, and therefore can increase SNR.  Using diversity receive can make a big difference too.

Howard