Hi Alex,
My firm, DAVIS RF Co., advises hams, commercial entities and Mil / Gov't very
often with questions such as yours. We also have the lowest prices of any ham
dealer for Times LMR, Andrew / Commscope Heliax Tm, and an excellent
substitute for Andrew Heliax, which is RFS Cable Wave, an equivalent to
Heliax, at notably lower price.
LMR 600 is often what I hear from hams for VHF / UHF at a $ expenditure
that is doable. However, many of them change to RFS 1/2" when I note the fact
that it is
slightly lower loss at 6 m., has a bend radius of 3", vs. 6" for LMR-600, and
the fact that is is notably less expensive than LMR 600, or Andrew 1/2" Heliax.
RFS is a high quality cable and the connector cost is similar. Plus we will
install connectors using mfr. certified installers.
All accessories of the above 3 noted mfrs (connectors, shield grounding,
hangers, etc) are also lowest priced.
Lastly, we provide free shipping on orders over $ 75.00, which would apply
to your noted scenario.
I will contact you directly for more info and then give you a detailed
assessment showing attenuation figures dB and actual power attenuation based on
your xmtr output,. frequency and length of cable. I will also include LMR -400
just in case that makes sense to you.
We are the only ham dealer that I am aware of that provides such detailed info.
I am a cable design engineer and ham of over 50 years.
73, Steve, K1PEK, DAVIS RF Co., Division of Orion Wire Co., Inc.
________________________________
When replying, please edit your Subject line so it is more specific
than "Re: Contents of TowerTalk digest..."
Today's Topics:
1. looking for good coax for 6m (Alex Malyava)
3. Re: looking for good coax for 6m (David Gilbert)
lux)
1
----------------------------------------------------------------------
Message: 1
Date: Thu, 12 Sep 2019 20:10:02 -0400
From: Alex Malyava <alex.k2bb@gmail.com>
To: towertalk <towertalk@contesting.com>
Subject: [TowerTalk] looking for good coax for 6m
Message-ID:
<CAMHr7dJAnGRDv88N0v5PTv6tGhbc-OA7DK-4vCciQH4_Gr=FNQ@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Hi all,
I am looking for good quality coax to use on 6m, in two different places:
- home station, 6 element yagi, used for regular dxing... I need about 50'
to run from the wall up to the tower. Then I have another 50' of Belden
9913F running from the wall to the radio.
- portable 8 element yagi used in dxpedition for EME. I need about 50-75'
of it.
For the home station - Will I be ok if I use another run of 9913F or I
better get larger cable with less attenuation? Do I need to replace
existing run of 9913F? I will hate to do it - it is in the walls and in the
ceiling space...
So far, it seems, the only option is LMR600....
Is there any alternative to it? I don't care about the weight of it at
home, but 75' of coax in the luggage will take whole suitcase by size and
weight :)
Any online sources with user-friendly prices?
Thanks,
Alex K2BB
soon - 5H3EME
------------------------------
Message: 2
Date: Thu, 12 Sep 2019 20:16:49 -0400
From: Shane Autrey <iam4thapack@gmail.com>
To: towertalk@contesting.com
Subject: [TowerTalk] WTB RTS System
Message-ID:
<CAB6O3Gj=YUN+VRcxcHmR4BnV=2xyAbUK08U=4AafKaVa_Ak5xw@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
I have a friend without internet access who is putting up a tower and after
hearing my plans to do a RTS he wants to do his own RTS. He is in the
market for a RTS setup (K0XG or Custom Metal Works) for a 55G and needs
either a ground mounted or elevated rotor base and 2 guy rings. I will show
him the photos and he can decide what he wants to do. Email me direct with
what you have in mind please.
Shane
------------------------------
Message: 3
Date: Thu, 12 Sep 2019 17:34:40 -0700
From: David Gilbert <xdavid@cis-broadband.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] looking for good coax for 6m
Message-ID: <b06bc20f-1860-79ff-dee3-ce288a1e1893@cis-broadband.com>
Content-Type: text/plain; charset=utf-8; format=flowed
It seems to me that you are the only one who would know how much loss
you are willing to accept.? The specs for just about every imaginable
type of coax are readily available online.
For example, 50 feet of 9913F7 has a loss of 0.55 dB and LMR600 has a
loss of 0.35 dB.? I'm not sure if anyone here is going to know if that
0.2 dB is important to you or not ... but I'm going to guess not.
73,
Dave?? AB7E
On 9/12/2019 5:10 PM, Alex Malyava wrote:
> Hi all,
> I am looking for good quality coax to use on 6m, in two different places:
> - home station, 6 element yagi, used for regular dxing... I need about 50'
> to run from the wall up to the tower. Then I have another 50' of Belden
> 9913F running from the wall to the radio.
> - portable 8 element yagi used in dxpedition for EME. I need about 50-75'
> of it.
>
> For the home station - Will I be ok if I use another run of 9913F or I
> better get larger cable with less attenuation? Do I need to replace
> existing run of 9913F? I will hate to do it - it is in the walls and in the
> ceiling space...
>
> So far, it seems, the only option is LMR600....
> Is there any alternative to it? I don't care about the weight of it at
> home, but 75' of coax in the luggage will take whole suitcase by size and
> weight :)
>
> Any online sources with user-friendly prices?
>
> Thanks,
> Alex K2BB
> soon - 5H3EME
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
------------------------------
Message: 4
Date: Thu, 12 Sep 2019 21:02:26 -0400
From: Roger D Johnson <n1rj@roadrunner.com>
To: Towertalk Reflector <towertalk@contesting.com>
Subject: [TowerTalk] Skip Distance
Message-ID: <73d0cb8e-6d64-fa69-99ef-26c3d89154d5@roadrunner.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
I've been running some tests on my 8 circle array with K1JB. Joe is 17 miles
away and I sometimes notice deep fading on his signal. Makes plotting the
antenna pattern very difficult. Is it possible to have skywave contamination
at this short range?
73, Roger
------------------------------
Message: 5
Date: Thu, 12 Sep 2019 20:05:29 -0500
From: john@kk9a.com
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cushcraft/MFJ Traps
Message-ID:
<20190912200529.Horde.wyweXbPhMHspPPW3HTo27R2@www11.qth.com>
Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes
SteppIR beam do not have traps but they use a fixed element spacing as
mentioned in your tribander post. Has any SteppIR owner done the
modeling work to see what effect this really has?
John KK9A
David Gilbert AB7E wrote:
Trapped tribanders have shorter elements, which has an effect on
pattern, and they have non-optimal element spacing for any particular
band, which again affects pattern gain.
Dave AB7E
------------------------------
Message: 6
Date: Thu, 12 Sep 2019 18:25:48 -0700
From: Wes <wes_n7ws@triconet.org>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cushcraft/MFJ Traps
Message-ID: <fc1194bf-b49d-76ce-746e-38bf7e9bead6@triconet.org>
Content-Type: text/plain; charset=utf-8; format=flowed
https://ac6la.com/aecollection10.html
On 9/12/2019 6:05 PM, john@kk9a.com wrote:
> SteppIR beam do not have traps but they use a fixed element spacing as
> mentioned in your tribander post. Has any SteppIR owner done the modeling work
> to see what effect this really has?
>
>
> John KK9A
>
>
>
> David Gilbert AB7E wrote:
>
>
> Trapped tribanders have shorter elements, which has an effect on
> pattern, and they have non-optimal element spacing for any particular
> band, which again affects pattern gain.
>
>
> Dave?? AB7E
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
------------------------------
Message: 7
Date: Thu, 12 Sep 2019 21:11:28 -0700
From: Grant Saviers <grants2@pacbell.net>
To: john@kk9a.com, towertalk@contesting.com
Subject: Re: [TowerTalk] Cushcraft/MFJ Traps
Message-ID: <7b5e8026-2c62-b349-02d9-00cc1c6350c4@pacbell.net>
Content-Type: text/plain; charset=utf-8; format=flowed
All of the SteppIR antenna EZNEC models are available in Dan AC6LA's
great AutoEZ tool format so you can vary the element lengths. Pretty
complex models, not good as a first experience.
Here is the link to Dan's introduction and models
https://ac6la.com/aecollection10.html
Grant KZ1W
On 9/12/2019 6:05 PM, john@kk9a.com wrote:
> SteppIR beam do not have traps but they use a fixed element spacing as
> mentioned in your tribander post. Has any SteppIR owner done the
> modeling work to see what effect this really has?
>
>
> John KK9A
>
>
>
> David Gilbert AB7E wrote:
>
>
> Trapped tribanders have shorter elements, which has an effect on
> pattern, and they have non-optimal element spacing for any particular
> band, which again affects pattern gain.
>
>
> Dave???? AB7E
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
------------------------------
Message: 8
Date: Thu, 12 Sep 2019 21:32:01 -0700
From: David Gilbert <xdavid@cis-broadband.com>
To: Towertalk <towertalk@contesting.com>
Subject: [TowerTalk] One way skip explained
Message-ID: <dcea0a03-f0b9-3023-fa82-5683137a97d4@cis-broadband.com>
Content-Type: text/plain; charset=utf-8; format=flowed
It was due to the time and space varying nature of the density of the
atmosphere all along ...
https://www.sciencedaily.com/releases/2019/09/190912111010.htm
Just kidding, of course, but it is pretty interesting.
Dave
------------------------------
Message: 9
Date: Fri, 13 Sep 2019 06:11:13 -0400
From: Roger D Johnson <n1rj@roadrunner.com>
To: Towertalk Reflector <towertalk@contesting.com>, Top Band Reflector
<topband@contesting.com>
Subject: Re: [TowerTalk] Skip Distance
Message-ID: <9dc97e1b-70bc-8243-c003-53f47b8b10f6@roadrunner.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
These test were in late morning to early afternoon.
73, Roger
On 9/12/2019 9:02 PM, Roger D Johnson wrote:
> I've been running some tests on my 8 circle array with K1JB. Joe is 17 miles
> away and I sometimes notice deep fading on his signal. Makes plotting the
> antenna pattern very difficult. Is it possible to have skywave contamination
> at this short range?
>
> 73, Roger
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
------------------------------
Message: 10
Date: Fri, 13 Sep 2019 11:47:32 +0000 (UTC)
From: cqtestk4xs@aol.com
To: TOWERTALK@contesting.com
Subject: [TowerTalk] Rotating tower failures
Message-ID: <1992980767.6854232.1568375252651@mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8
I've had four rotating towers...never an issue.
I can speak to K4JA's tower failure.? I visited his station in the early 2000s
and had a chance to check out the tower installation.? I was amazed at how
loose the guy wires were.? They were no where near tensioned what a standard
tower would be.? I asked about this and was told there were rotation issues if
the guys were tensioned up to the usual specs.? The tower rotation system was
(I think) by K4JA's brother and was not a K0XG design.? The tower was an
accident waiting to happen whether it was a rotating tower or fixed. The guys
were way to sloppy for my taste.
Bill KH7XS/K4XS
------------------------------
Message: 11
Date: Fri, 13 Sep 2019 12:08:31 +0000 (UTC)
From: cqtestk4xs@aol.com
To: towertalk@contesting.com
Subject: [TowerTalk] Polygon fiberglass
Message-ID: <1450181114.6846350.1568376511888@mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8
I've used this stuff extensively at three different stations with 60-200 ft
towers, so I know what I am talking about.
First, unless one is really clueless, the stuff is quite easy to work with.?
I've probably unrolled 6000 or 7000 feet of new Polyrod and NEVER had an
issue.? In a clear area I "walked" out around 200 feet for the guys and cut it
with a hacksaw...no breaks, cracks etc.? It was real easy.? Only caveat is to
wear gloves.?
When I sold my station in 2006 I sold some to guys in Ohio and much of it? to a
guy in FL.? In order to do this I needed to roll it back up in an 8 ft diameter
for transport.? Again easy to do with gloves.? When I returned to FL I bought
back the stuff I sold to the guy in FL and purchased some new stuff.? Even in
the FL sun after 10 years the old stuff was in great shape and I had no issues
using it.? The tower installation in FL (3-200 footers) is still standing using
it...after 18 years.? And that is after several brushes with hurricanes.
The tower out in KH6 has new Polyrod? and again no issues.??
Cons:
Guy grips for the rod are available from PLP, but you must buy a box of 25.You
must wear gloves when handling it.You must adhere to the 8 ft diameter when?
working with it...it will crack.You must buy a full 1000 ft roll or more.Harder
to store
Pros:
Easier to install guy grips than PhillyAbout 1/2 the cost of PhillyMore
resistance to abrasion
YMMV.
Bill KH7XS/K4XS
------------------------------
Message: 12
Date: Fri, 13 Sep 2019 05:38:51 -0700
From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cushcraft/MFJ Traps
Message-ID: <b455cb1c-e905-786b-2d98-6d2b370fddc1@earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed
On 9/12/19 12:42 PM, Jim Brown wrote:
> I have two very different takes on this. First, traps are an inefficient
> way to build a multi-band antenna. That means they suck up gain. Also,
> because the elements are shorter, their radiation efficiency is reduced.
> The best multiband antennas don't use traps.
I'm not so sure about the efficiency aspect for shorter antennas - sure,
for "very short", the matching network losses will increase, but the
actual antenna efficiency isn't different (I^2*R losses are usually
pretty low)
Take a 6 meter long dipole as an example. REsonant at roughly 24 MHz -
here's the feedpoint impedance
f r x
23.6 77.6359 -12.4921
23.8 79.7763 -2.8992
24 81.976 6.6949
24.2 84.237 16.2932
24.4 86.5613 25.8988
Now let's drop to 18 MHz, so the dipole would be 75% of resonant length
f r x
17.6 33.6036 -316.66
17.8 34.6034 -305.433
18 35.6276 -294.325
18.2 36.6769 -283.331
18.4 37.7518 -272.445
So you'd need some sort of matching network to cancel out the 300 ohm
reactance. It's pretty easy to come up with a coil that has a Q of 200,
so the 300 ohm coil would have a resistance of 1.5 ohms. Compared to the
36 ohm radiation resistance, that's about 4% or 0.2 dB.
At 50% length:
11.8 12.9553 -732.472
12 13.4523 -713.564
12.2 13.9618 -695.14
Now we're starting to be significant, a inductor Q of 200 is going to be
around 3.5 ohms loss resistance, and against 13.5 ohms antenna R, that's
a 20% loss (1 dB).
Of course, for many HF links, on receive, the SNR is determined by the
atmospheric noise, and antenna gain (for lowish gain antennas < 10dB)
doesn't change the received SNR - the reduced gain drops both the
desired signal and the noise level.
For transmit, of course, it does affect the SNR that the other end sees.
------------------------------
Message: 13
Date: Fri, 13 Sep 2019 05:43:52 -0700
From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Skip Distance
Message-ID: <e127184f-ea64-71f4-4692-1f83a189e3d6@earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed
On 9/12/19 6:02 PM, Roger D Johnson wrote:
> I've been running some tests on my 8 circle array with K1JB. Joe is 17
> miles away and I sometimes notice deep fading on his signal. Makes
> plotting the
> antenna pattern very difficult. Is it possible to have skywave
> contamination
> at this short range?
>
What frequency are you at and what time of day?
It's entirely possible to get skywave. At some frequency, vertical
incidence reflects straight back down.
You might look for an ionosonde near you - these days, many ionosondes
put their plots online in near real time.
------------------------------
Message: 14
Date: Fri, 13 Sep 2019 05:59:00 -0700
From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] One way skip explained
Message-ID: <1015ea54-84b6-8106-801c-0a63dc494760@earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed
On 9/12/19 9:32 PM, David Gilbert wrote:
>
> It was due to the time and space varying nature of the density of the
> atmosphere all along ...
>
> https://www.sciencedaily.com/releases/2019/09/190912111010.htm
>
> Just kidding, of course, but it is pretty interesting.
>
It is interesting, but you can explain one-way skip fairly easily - the
ionosphere propagates with two modes (O and X, opposite circular
polarizations) - the skip distance is different for the two, and if
you're at the edge of the skip zone, you're in that "caustic" (aka
bright line) where the signal is stronger than a simple distance
calculation would give you, but only for one polarization.
If it's a multihop path it gets even more complex, because the
polarization changes sense when reflecting off the Earth's surface, so
there's some fairly complex combination of the modes.
------------------------------
Message: 15
Date: Fri, 13 Sep 2019 06:08:55 -0700
From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Skip Distance
Message-ID: <f56fa87b-cee9-e5ad-f706-b0f788b8000d@earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed
On 9/13/19 3:11 AM, Roger D Johnson wrote:
> These test were in late morning to early afternoon.
At what frequency - I think we can assume the SSN is low, low, low..
>
> 73, Roger
>
> On 9/12/2019 9:02 PM, Roger D Johnson wrote:
>> I've been running some tests on my 8 circle array with K1JB. Joe is 17
>> miles away and I sometimes notice deep fading on his signal. Makes
>> plotting the
>> antenna pattern very difficult. Is it possible to have skywave
>> contamination
>> at this short range?
>>
>> 73, Roger
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
------------------------------
Message: 16
Date: Fri, 13 Sep 2019 08:17:10 -0500
From: john@kk9a.com
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cushcraft/MFJ Traps
Message-ID:
<20190913081710.Horde.r4LSr57LAN2ehgQLU56x1pV@www11.qth.com>
Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes
I currently have a pair of 2el shorty 40's made by Optibeam, model
OB2-40. These use a high Q coil in the center of the elements for
loading and have an 18' boom. For months I have been modeling various
full size 40m Yagis and comparing them to my small antennas. Larger
antennas have more bandwidth but I have been amazed at the efficiency
(at least in my model) of OptiBeam's shortened elements. If I replace
my current small 75 pound antennas with two full sized 350 pound 4
element OWA beams on a 48 ft boom, I will be only 2dB louder.
John KK9A
jimlux wrote:
On 9/12/19 12:42 PM, Jim Brown wrote:
> I have two very different takes on this. First, traps are an
> inefficient way to build a multi-band antenna. That means they suck
> up gain. Also, because the elements are shorter, their radiation
> efficiency is reduced. The best multiband antennas don't use traps.
I'm not so sure about the efficiency aspect for shorter antennas - sure,
for "very short", the matching network losses will increase, but the
actual antenna efficiency isn't different (I^2*R losses are usually
pretty low)
Take a 6 meter long dipole as an example. REsonant at roughly 24 MHz -
here's the feedpoint impedance
f r x
23.6 77.6359 -12.4921
23.8 79.7763 -2.8992
24 81.976 6.6949
24.2 84.237 16.2932
24.4 86.5613 25.8988
Now let's drop to 18 MHz, so the dipole would be 75% of resonant length
f r x
17.6 33.6036 -316.66
17.8 34.6034 -305.433
18 35.6276 -294.325
18.2 36.6769 -283.331
18.4 37.7518 -272.445
So you'd need some sort of matching network to cancel out the 300 ohm
reactance. It's pretty easy to come up with a coil that has a Q of 200,
so the 300 ohm coil would have a resistance of 1.5 ohms. Compared to the
36 ohm radiation resistance, that's about 4% or 0.2 dB.
At 50% length:
11.8 12.9553 -732.472
12 13.4523 -713.564
12.2 13.9618 -695.14
Now we're starting to be significant, a inductor Q of 200 is going to be
around 3.5 ohms loss resistance, and against 13.5 ohms antenna R, that's
a 20% loss (1 dB).
Of course, for many HF links, on receive, the SNR is determined by the
atmospheric noise, and antenna gain (for lowish gain antennas < 10dB)
doesn't change the received SNR - the reduced gain drops both the
desired signal and the noise level.
For transmit, of course, it does affect the SNR that the other end sees.
------------------------------
Message: 17
Date: Fri, 13 Sep 2019 06:24:27 -0700
From: jimlux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cushcraft/MFJ Traps
Message-ID: <4dd0e48d-68ff-f7d1-bd6e-7bf44a141f3b@earthlink.net>
Content-Type: text/plain; charset=utf-8; format=flowed
On 9/13/19 6:17 AM, john@kk9a.com wrote:
> I currently have a pair of 2el shorty 40's made by Optibeam, model
> OB2-40. These use a high Q coil in the center of the elements for
> loading and have an 18' boom.? For months I have been modeling various
> full size 40m Yagis and comparing them to my small antennas. Larger
> antennas have more bandwidth but I have been amazed at the efficiency
> (at least in my model) of OptiBeam's shortened elements.? If I replace
> my current small 75 pound antennas with two full sized 350 pound 4
> element OWA beams on a 48 ft boom, I will be only 2dB louder.
I think the OB2-40 has 10 meter long elements, which is about 50% of the
full size resonant dipole for 40 meters.
Your modeled 2dB change is fully consistent with the calculation below..
As someone else pointed out, you do potentially give up some gain from a
physically shorter antenna - or a narrower bandwidth, or something else.
(TANSTAAFL)
There's even an equation for it: The Chu-Harrington formula tells you
the tradeoff between physical size, Q, directivity
https://en.wikipedia.org/wiki/Chu%E2%80%93Harrington_limit
>
> John KK9A
>
> jimlux wrote:
>
> On 9/12/19 12:42 PM, Jim Brown wrote:
>
>> I have two very different takes on this. First, traps are an
>> inefficient way to build a multi-band antenna. That means they suck up
>> gain. Also, because the elements are shorter, their radiation
>> efficiency is reduced. The best multiband antennas don't use traps.
>
> I'm not so sure about the efficiency aspect for shorter antennas - sure,
> for "very short", the matching network losses will increase, but the
> actual antenna efficiency isn't different (I^2*R losses are usually
> pretty low)
>
> Take a 6 meter long dipole as an example. REsonant at roughly 24 MHz -
> here's the feedpoint impedance
> f??? r??? x
> 23.6???? 77.6359 -12.4921
> 23.8???? 79.7763 -2.8992
> 24???? 81.976???? 6.6949
> 24.2??? 84.237 16.2932
> 24.4???? 86.5613 25.8988
>
> Now let's drop to 18 MHz, so the dipole would be 75% of resonant length
> f??? r??? x
> 17.6???? 33.6036 -316.66
> 17.8???? 34.6034 -305.433
> 18???? 35.6276 -294.325
> 18.2???? 36.6769 -283.331
> 18.4???? 37.7518 -272.445
>
> So you'd need some sort of matching network to cancel out the 300 ohm
> reactance. It's pretty easy to come up with a coil that has a Q of 200,
> so the 300 ohm coil would have a resistance of 1.5 ohms. Compared to the
> 36 ohm radiation resistance, that's about 4% or 0.2 dB.
>
> At 50% length:
>
> 11.8 12.9553 -732.472
> 12 13.4523 -713.564
> 12.2 13.9618 -695.14
>
> Now we're starting to be significant, a inductor Q of 200 is going to be
> around 3.5 ohms loss resistance, and against 13.5 ohms antenna R, that's
> a 20% loss (1 dB).
>
> Of course, for many HF links, on receive, the SNR is determined by the
> atmospheric noise, and antenna gain (for lowish gain antennas < 10dB)
> doesn't change the received SNR - the reduced gain drops both the
> desired signal and the noise level.
>
> For transmit, of course, it does affect the SNR that the other end sees.
>
>
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End of TowerTalk Digest, Vol 201, Issue 38
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