[RSM] RSM Digest, Vol 52, Issue 13

[ed_richardson at shaw.ca]

Awful is such a relative term when comparing antennas.  A couple things with the twinlead fed dipole antenna I (and others) have found. 

- This is a balanced antenna.  That means both legs must be the same length and be configured in as straight a line as practical. 
- You require a good quality balun at the junction of the coax and twin lead.  Something like a DX engineering or Balun Designs 1:1 design.
- Isolate the twinlead away from the support structure (House, tower, tree)
- The twin lead should be 300 ohm, not 450 or 600 ohm.
- The twin lead must be at least 1/4 wave at the lowest operating frequency.
- The VSWR between the tuner output and the balun can be quite high. Keep this distance as short as practical to minimize losses. Use  RG213 or larger coax for this run.

If you unbalance the antenna, (unequal lengths, poor quality balun, feedline too close to the building) the twin lead will indeed start to pick up noise.

In the end, you will still have a 130 foot long piece of wire. How well it radiates still depends on how high it is and the proximity to other structures. It isn’t a great DX antenna but will work well for domestic purposes.


Ed Richardson

-----Original Message-----
From: RSM <rsm-bounces at contesting.com> On Behalf Of ve4dla at gmail.com
Sent: January 29, 2021 1:34 PM
To: rsm at contesting.com
Subject: Re: [RSM] RSM Digest, Vol 52, Issue 13

Thanks Ed. I tried that antenna before the gap, was awful. Of course, I had 450 ohm window line not tv ribbon. 

Sent from my iPhone

> On Jan 29, 2021, at 11:01, rsm-request at contesting.com wrote:
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> Today's Topics:
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>   1. so many antennas, so little room (David Latour)
>   2. Re: so many antennas, so little room (ed_richardson at shaw.ca)
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> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Thu, 28 Jan 2021 12:07:48 -0600
> From: David Latour <ve4dla at gmail.com>
> To: rsm at contesting.com
> Subject: [RSM] so many antennas, so little room
> Message-ID:
>    
> <CAPjHFekfPGbh07fdfXdoF8M52U13Zw6tjQDObYTHQGPp+RVOfA at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
> 
> This Spring I will have to return the GAP Titan to its owner. I have 
> in a box an OCFD that has never been put up (paid a whole $5, balun 
> included). I have on order a balun for a military fan dipole, but it 
> may never arrive (didn't 2 years ago.) I have JUST enough space for an 
> 80-10m EFLW, but it will be pricey to fit up the parts from the 
> States. Does anyone have much real experience with either of these? 
> Advice is always welcome. I can get any of these 20' above my roof (13') on fiberglass poles.
> 
> --
> 73 de David VE4DL
> 
> 
> ------------------------------
> 
> Message: 2
> Date: Thu, 28 Jan 2021 13:33:37 -0600
> From: <ed_richardson at shaw.ca>
> To: "'rsm'" <rsm at contesting.com>
> Subject: Re: [RSM] so many antennas, so little room
> Message-ID: <068701d6f5ac$7aa5e200$6ff1a600$@shaw.ca>
> Content-Type: text/plain;    charset="us-ascii"
> 
> Hi David
> 
> I had good success with a 132 foot wire fed in the center using 300 
> ohm ladder line. Essentially an 80m dipole. You would need a good 1:1 
> balun at the shack end of the 300 ohm line. Also a tuner is required 
> but I was able to work all bands from 80 to 6m.
> 
> I would avoid the end fed long wires as they require a good 
> counterpoise or else you will likely suffer rf in the shack.
> 
> Have you tried any of the antenna modelling programs to visualize the 
> differences?
> 
> 
> Ed Richardson
> 
> -----Original Message-----
> From: RSM <rsm-bounces at contesting.com> On Behalf Of David Latour
> Sent: January 28, 2021 12:08 PM
> To: rsm at contesting.com
> Subject: [RSM] so many antennas, so little room
> 
> This Spring I will have to return the GAP Titan to its owner. I have 
> in a box an OCFD that has never been put up (paid a whole $5, balun 
> included). I have on order a balun for a military fan dipole, but it 
> may never arrive (didn't 2 years ago.) I have JUST enough space for an 
> 80-10m EFLW, but it will be pricey to fit up the parts from the 
> States. Does anyone have much real experience with either of these? 
> Advice is always welcome. I can get any of these 20' above my roof (13') on fiberglass poles.
> 
> --
> 73 de David VE4DL
> _______________________________________________
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> RSM at contesting.com
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> End of RSM Digest, Vol 52, Issue 13
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