RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > HF / MW / LW Monitoring > Receive Antennas (below 30MHz)


Receive Antennas (below 30MHz) - For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 07-13-2018, 4:59 PM
Member
   
Join Date: Jun 2017
Posts: 31
Default Shortwave antennas

I have an end fed long wire that I would like to get up this weekend. I was wondering about the coax going from the radio to the antenna, will any coils or turns have a direct impact on the receiving side of things? Itís going to plug into my Icom R75, so no transmitting will be going on. Just wondering if I need to snake the coax out or if I can coil up the slack.

Thanks,
Ryan
Reply With Quote
Sponsored links
  #2 (permalink)  
Old 07-13-2018, 5:08 PM
Wiki Admin Emeritus
  Amateur Radio Operator
Amateur Radio
 
Join Date: Jul 2002
Location: Bowie, Md.
Posts: 21,360
Default

Depends. Coiling up the coax does have advantages when wound around a core; you can create a method of removing common currents which can carry noise into the receiver. Without it, you might have some attenuation issues if there's enough of the coax coiled, particularly if the length is around 1/4 wavelength on a given frequency or so. I'd avoid coiling it up if at all possible. And with turns, as long as they're not sharp and cause bends, no problem - just avoid pinching the coax and keep the turns as gentle as you can...Mike
__________________
co-author, HF Digital Decoding
HF Forum moderator, RadioReference
Friends don't let friends buy Scancat Lite Plus!
Reply With Quote
  #3 (permalink)  
Old 07-13-2018, 5:12 PM
Member
   
Join Date: Jun 2017
Posts: 31
Default

I’ll try to keep it straight then. It’s coming out my upstairs window and it will be secured to the roof of my garage and run to the antenna that way. By running it on the roof I have plenty of room to keep it straight.
Reply With Quote
  #4 (permalink)  
Old 07-13-2018, 6:47 PM
majoco's Avatar
Member
  Shack Photos
Shack photos
 
Join Date: Dec 2008
Location: New Zealand
Posts: 2,948
Default

IMHO what is more important is an un-un at the end of the wire to the coax to match the antenna to the receiver.
__________________
Cheers - Martin ZL2MC - Palmerston North
Reply With Quote
  #5 (permalink)  
Old 07-14-2018, 4:23 AM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Feb 2014
Posts: 495
Default

Quote:
Originally Posted by majoco View Post
IMHO what is more important is an un-un at the end of the wire to the coax to match the antenna to the receiver.
this ^^^

The antenna will perform better with a matching device such as a 9:1 unun.

Also, consider some lightning protection.
Reply With Quote
Sponsored links
  #6 (permalink)  
Old 07-14-2018, 11:43 AM
Member
  Premium Subscriber
Premium Subscriber
Amateur Radio Operator
Amateur Radio
 
Join Date: Feb 2015
Location: where they make the cheese
Posts: 251
Default

^^^^
something as simple as this will make it soooo much better
https://www.amazon.com/NooElec-Balun.../dp/B00R09WHT6
or
https://www.amazon.com/MagiDeal-100K.../dp/B078R4JSPB
Reply With Quote
  #7 (permalink)  
Old 07-14-2018, 2:32 PM
Member
   
Join Date: Jun 2017
Posts: 31
Default

I got the antenna up and I’ll see how it performs tonight. Was able to get Radio Havana on a quick test. Can someone explain in layman’s terms what these matching devices do?

Ryan
Reply With Quote
  #8 (permalink)  
Old 07-14-2018, 4:14 PM
majoco's Avatar
Member
  Shack Photos
Shack photos
 
Join Date: Dec 2008
Location: New Zealand
Posts: 2,948
Default

To get the best signal transfer from antenna to receiver the impedances should be the same. It is generally assumed that the overall impedance of a long-ish wire is about 450ohms while the input impedance of your radio is 50ohms. To match these two tegoether we use a transformer of ratio 450/50 = 9 to 1.
In this case...
https://www.amazon.com/MagiDeal-100K.../dp/B078R4JSPB
..they have called it a balun as well as a transformer which is not really true - balun means BALanced to UNbalanced but the they have shown an UN-UN. The single wire is unbalanced and so is the coaxial to you radio. For $10 you can't go wrong - although the suggestion that you waterproof the box is a good one. Better would be to bring the end of your wire through a window frame and have the box indoors although this may bring in some RF noise from your house.
Everyone call them 'longwires' but in fact they are not long enough! A proper longwire is more than a wavelength so if you want to listen to the 6MHz broadcast band you should have more than 55yards of wire!
__________________
Cheers - Martin ZL2MC - Palmerston North

Last edited by majoco; 07-14-2018 at 4:18 PM..
Reply With Quote
  #9 (permalink)  
Old 07-14-2018, 4:26 PM
Member
   
Join Date: Jun 2017
Posts: 31
Default

That makes sense. I didn’t know these little devices existed, and super cheap too. Thanks for the explanation.
Reply With Quote
  #10 (permalink)  
Old 07-15-2018, 5:49 PM
Member
   
Join Date: May 2009
Posts: 2,405
Default

In the case of the NooElec balun, just know that there is a single copper trace on the back, which you can scratch through to make it galvanically, aka a physically isolated transformer, which can help to keep common-mode coax braid from being part of your antenna system.

The R75 also has a built-in 10:1 transformer which you can switch to. Normally this is used for high-impedance feedlines like 300-600 ohm twinlead. OR, end-fed wires.

Normally most don't use it because of the indoor noise problem, but you can also try this little trick on some bands with your existing setup:

Disconnect the coax cable from the back of the R75. Run a small jumper from the high-impedance push-in jack to the center conductor, maybe with a little alligator clip jumper, make the antenna switch in the R75, and see if it improves or degrades your reception depending on frequency.

Don't forget to switch the R75 back to the coax antenna when you screw the coax back in for use in that mode.

These are just general purpose notes, since we don't know how bad noise is at your location. It's a simple thing to try however just for fun.
Reply With Quote
  #11 (permalink)  
Old 07-15-2018, 6:31 PM
ridgescan's Avatar
Member
  Shack Photos
Shack photos
 
Join Date: Apr 2008
Location: San Francisco, Ca.
Posts: 4,399
Default

Quote:
Originally Posted by hertzian View Post
In the case of the NooElec balun, just know that there is a single copper trace on the back, which you can scratch through to make it galvanically, aka a physically isolated transformer, which can help to keep common-mode coax braid from being part of your antenna system.

The R75 also has a built-in 10:1 transformer which you can switch to. Normally this is used for high-impedance feedlines like 300-600 ohm twinlead. OR, end-fed wires.

Normally most don't use it because of the indoor noise problem, but you can also try this little trick on some bands with your existing setup:

Disconnect the coax cable from the back of the R75. Run a small jumper from the high-impedance push-in jack to the center conductor, maybe with a little alligator clip jumper, make the antenna switch in the R75, and see if it improves or degrades your reception depending on frequency.

Don't forget to switch the R75 back to the coax antenna when you screw the coax back in for use in that mode.

These are just general purpose notes, since we don't know how bad noise is at your location. It's a simple thing to try however just for fun.
Good tips hertzian I did not know that about my R75. I will try this "just for fun" too. All about experimentation in this thing.
__________________
BC785D to Diamond D130J @50'
Icom R8600, RS DX-160 to Wellbrook loop @50'
Icom R75,
'54 SX-88 #127 to 100' endfed wire/9:1 trans. @40'
RS Pro 2066 in truck to Larsen Tribander
Reply With Quote
  #12 (permalink)  
Old 07-15-2018, 11:19 PM
Member
   
Join Date: Jul 2013
Location: Te Pahu, New Zealand
Posts: 23
Default

Hi to the group.
I am an old SWL having used a Realistic DX-160 in the 1970s, a Yaesu FRG-7 in the 1980s and in 1998 acquired a Drake R8B (with VHF) that I continue to enjoy today.
I have been using an Alpha Delta 62' DX-SWL Sloper and an AOR DA3000 Discone both connected by RG58U coax to the radio through Antenna Supermarket Zap Trappers and Alpha Delta Antenna Switches.
I live near Te Pahu, a rural area of New Zealand about 20km west of Hamilton and 20 km from the Tasman Sea at Raglan on the west coast of the North Island.
On a good night I can hear most NZ BCB stations but seldom an Australian. Get HF BCB stations in all the bands from 49M to 16M Europe, North and South America, Africa, Asia and Pacific Islands, depending of course on the conditions and time of day. Same with the hams on 75M, 40M and 20M from all over the world and Aero HF South and Central Pacific sometimes to SFO.
All in all I'm very happy with the reception I get but am wondering about the impedance matching I read about here. I understand the math around frequency and antenna length but have never fully groked the balanced/unbalanced ratios etc.
Mentioned below are the MagiDeal 100K and NooElec-Balun available from Amazon for less than $20.
Do any of our resident experts have an opinion as to whether such add ons would be of any benefit to my setup?
Many thanks.
Rick
Te Pahu
Reply With Quote
  #13 (permalink)  
Old 07-16-2018, 12:27 AM
Member
   
Join Date: May 2009
Posts: 2,405
Default

Hi Rick!

I think just changing your directionality would be of the most benefit. For picking up Australian BCB, you could just try moving your sloper around.

Better yet, would be to try an AM loop antenna. There are plenty of BCB loop antenna projects detailed around, but here is an easy one, although you probably don't want to put your R8 in the middle of it - use a coax jumper instead:

https://www.youtube.com/watch?v=Wnkf_gQQwwg

As for the transformers / baluns, that all depends - mostly on what you can support in your environment with the emphasis on what direction do you want to receive?

For example, a very simple dipole with a 1:1 choke balun could do wonders if you aim it right rather than using an end-fed that needs a high impedance transformer.

I'm not totally sure if you are asking if replacing the existing matching network in your Alpha Delta would be beneficial, or build something like it yourself with a transformer / balun? Short answer - don't carve up your Alpha Delta - leave it be!

Last edited by hertzian; 07-16-2018 at 12:46 AM..
Reply With Quote
  #14 (permalink)  
Old 07-16-2018, 4:29 AM
majoco's Avatar
Member
  Shack Photos
Shack photos
 
Join Date: Dec 2008
Location: New Zealand
Posts: 2,948
Default

I go past your place on my way to my step-daughters in Auckland - I always go around the western side of the mountain and often stop in Pirongia when the low caffeine light goes on!
Anyway, try for the NDB's on Norfolk Island (260kHz) and Lord Howe (272kHZ). This will give you an idea if your antenna is suspect, Norfolk Booms in here after 10pm in the winter. To get the Oz BC band you really need both ends to be in good darkness so any earlier than 11pm is doomed to fail - and of course the NZ BC band uses the same frequencies so you are more likely to hear them rather than the Oz stations.
__________________
Cheers - Martin ZL2MC - Palmerston North
Reply With Quote
  #15 (permalink)  
Old 07-16-2018, 7:10 AM
Member
  Amateur Radio Operator
Amateur Radio
 
Join Date: Feb 2014
Posts: 495
Default

Rick,

Your Drake is a fine receiver. What you need is another antenna or two or three to get the most out of it. Try running them in different directions. As mentioned, a loop can produce amazing results especially on the BCB with its ability to peak/null. A broadband matching device or an antenna tuner also helps considerably. Be sure to use the proper antenna inputs on your receiver (hi or lo Z) to best match the antenna connected to it.
Reply With Quote
  #16 (permalink)  
Old 07-16-2018, 4:37 PM
a29zuk's Avatar
Member
   
Join Date: Mar 2005
Location: SE Michigan
Posts: 554
Default

Quote:
Originally Posted by tuihill View Post
Hi to the group.
I am an old SWL having used a Realistic DX-160 in the 1970s, a Yaesu FRG-7 in the 1980s and in 1998 acquired a Drake R8B (with VHF) that I continue to enjoy today.

Many thanks.
Rick
Te Pahu
Do you still have the DX-160 and the FRG?
+1 for a different direction on the antenna! Always experiment with antennas.


Jim

Last edited by a29zuk; 07-16-2018 at 4:41 PM..
Reply With Quote
  #17 (permalink)  
Old 07-16-2018, 4:40 PM
a29zuk's Avatar
Member
   
Join Date: Mar 2005
Location: SE Michigan
Posts: 554
Default

Quote:
Originally Posted by majoco View Post
I go past your place on my way to my step-daughters in Auckland - I always go around the western side of the mountain and often stop in Pirongia when the low caffeine light goes on!
Did you order your caffeine light from Amazon?

Jim
Reply With Quote
  #18 (permalink)  
Old 07-16-2018, 5:25 PM
Member
   
Join Date: Jul 2013
Location: Te Pahu, New Zealand
Posts: 23
Default

Reply to Jim a29zuk
Do you still have the DX-160 and the FRG?

Sadly no. Been kicking myself for years.

Cheers,
Rick

Last edited by tuihill; 07-16-2018 at 5:30 PM.. Reason: include question answered
Reply With Quote
  #19 (permalink)  
Old 07-16-2018, 5:37 PM
Member
   
Join Date: Jul 2013
Location: Te Pahu, New Zealand
Posts: 23
Default

Quote:
Originally Posted by WA8ZTZ View Post
Rick,

Your Drake is a fine receiver. What you need is another antenna or two or three to get the most out of it. Try running them in different directions. As mentioned, a loop can produce amazing results especially on the BCB with its ability to peak/null. A broadband matching device or an antenna tuner also helps considerably. Be sure to use the proper antenna inputs on your receiver (hi or lo Z) to best match the antenna connected to it.
I've been looking at Wellbrook and AOR loops as well as a few others and home brews.
When I get to making a decision, I will first be wanting to sort out a simple remote rotator.
All it needs to do is swing through 90 degrees I think.

Cheers,
Rick
Reply With Quote
  #20 (permalink)  
Old 07-16-2018, 5:55 PM
Member
   
Join Date: Jul 2013
Location: Te Pahu, New Zealand
Posts: 23
Default

Quote:
Originally Posted by majoco View Post
I go past your place on my way to my step-daughters in Auckland - I always go around the western side of the mountain and often stop in Pirongia when the low caffeine light goes on!
Anyway, try for the NDB's on Norfolk Island (260kHz) and Lord Howe (272kHZ). This will give you an idea if your antenna is suspect, Norfolk Booms in here after 10pm in the winter. To get the Oz BC band you really need both ends to be in good darkness so any earlier than 11pm is doomed to fail - and of course the NZ BC band uses the same frequencies so you are more likely to hear them rather than the Oz stations.
Thanks Martin.

Awake at 300am and saw your suggestion.
Norfolk and Lord Howe quite clear. Norfolk slightly stronger.
My sloper is aligned high end south sloping down to north.
Checked through the BCB but could find any Aussie accents behind the NZ stations.
Will have another go next time I can't get back to sleep.

Cheers,
Rick
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 11:29 AM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2015 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions