[TenTec] 160 M antenna

[Bob McGraw - K4TAX]

Just pointed out that I have a typo.   Should be MFJ-259   for the analyzer.

73
Bob, K4TAX


----- Original Message ----- 
From: "Bob McGraw - K4TAX" <RMcGraw at Blomand.net>
To: <k9yc at arrl.net>; "Discussion of Ten-Tec Equipment" 
<tentec at contesting.com>
Sent: Wednesday, November 06, 2013 7:00 PM
Subject: Re: [TenTec] 160 M antenna


> Personally I typically evaluate any HF antenna that I use based on a 3:1 
> SWR bandwidth.  That better is defined as being the frequency that 
> produces a 3:1 SWR below the 1:1 SWR frequency and the frequency that 
> produces a 3:1 SWR above the 1:1 SWR frequency.   Using an Antenna Bridge 
> such as the MFJ-250 will do an excellent job finding these points.
>
> The reason I choose a 3:1 SWR value is the fact that Tentec PA circuits do 
> not have any issues with a SWR of this value or lower.  I can't say the 
> same for other brands.  And I find that any reasonable feedline, 
> discounting open wire lines, will have negligible loss with a 3:1 SWR or 
> less.
>
> All please note;  Jim K9YC has a very good explanation of radiation 
> resistance, wire resistance, and ground resistance and such in his post.
>
> 73
> Bob, K4TAX
>
>
>
>
> ----- Original Message ----- 
> From: "Jim Brown" <k9yc at audiosystemsgroup.com>
> To: <tentec at contesting.com>
> Sent: Wednesday, November 06, 2013 6:00 PM
> Subject: Re: [TenTec] 160 M antenna
>
>
>> On 11/6/2013 3:34 PM, resluder at yahoo.com wrote:
>>> What kind of bandwidth do you get with your inverted L, 50 kHz?  Would I 
>>> still be able to use a tuner in the shack if I want to bend it for more 
>>> coverage on 160?
>>
>> Define bandwidth.  Do you mean SWR bandwidth?  Do you mean you can get it 
>> to load?
>>
>> If you can get the total wire length > 100 ft and connect it to a decent 
>> radial system, a decent tuner should be able load it across all of 160M, 
>> but you'll need to retune it as you QSY.  The Ten Tec 229 and 238 series 
>> tuners work very well on 160M with reasonably good antennas.
>>
>> I have a Tee vertical for 160M that's 86 ft vertical with roughly 100 ft 
>> on top.  That makes it longer than a quarter wave, and I've adjusted the 
>> length of the top section so that the feedpoint Z is 50 ohms resistive 
>> plus some inductance (because it's electrically long).  I then added 
>> series C to tune out the L, giving me a nice match to 50 ohms.  I can 
>> work at least the bottom 75 kHz of 160M without much tuning.
>>
>> A well known way of broadbanding almost any antenna is to make the 
>> conductor fatter. An easy way to do that is to use two spaced conductors, 
>> tied together at both ends, and that's what I did.  The vertical is two 
>> #10 THHN wires spaced about 6 inches. I did that, and the SWR bandwidth 
>> improved by at least 50%.
>>
>> As to loading a 45 ft wire on 160M, which Jim asked about. I'd guess that 
>> the Ten tuners will LOAD it, but the radiation resistance of such a short 
>> wire is pretty low, so it won't be very efficient without a great radial 
>> system.  Remember that a vertical is a simple series circuit -- 
>> radiation resistance (Rr), wire resistance (Rw), and ground resistance 
>> (Rg).  The radiation resistance is the "good" resistance -- it accounts 
>> for radiated power, but the same current flows in all three resistors, so 
>> the power divides between them. For the antenna to WORK, we want Rr to be 
>> much larger than (Rw + Rg), but it takes a lot of wire to get Rg below 10 
>> ohms on 160M, and Rr of a 45 ft vertical won't be much more than perhaps 
>> 6 ohms, yielding an efficiency of about 30%. That means your 100W radio 
>> will put 70W into the ground and 30 watts into space.  .
>>
>> 73, Jim K9YC
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>
>
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