I used a MFJ ant analyzer to cut the 600 ohm feeders to length...with
analyzer at baluns input.
This might be a little more revelant...
SWR w/o TT 238A transmatch..in shack..with MFJ-259B ant analyzer
Feq SWR w/o tuner tuner settings Cap Low Z High Z Inductor
3.55 2.9:1 10 3
4.0
3.75 2:1 8.0 2
5.5
3.95 2.7 6.5 1
9.5
It appears to me that the transmatch setting swings are a bit wide to match
that little swr swing.
If I change the length of the 600 ohm feeders, then the 238A settings on 80
meters are less of a low Z/high Z swing.
As for the 4:1 balun, I homebrewed one using Jerry Sevick's design from his
Transmission Line Transfromers book.
----- Original Message -----
From: "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Friday, April 11, 2008 7:02 AM
Subject: Re: [TenTec] Ten Tec 238A settings?
> Calculation of impedances is great but nothing takes the place of actual
> measurement.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "Denton" <denton@oregontrail.net>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Friday, April 11, 2008 8:28 AM
> Subject: Re: [TenTec] Ten Tec 238A settings?
>
>
>>I use Eznec to calculate impendences....and also have tried a 1:1 and a
>>2:1
>> balun using same 600 ohm feeders...but nothing gives me as close a match
>> as
>> the 4:1 balun.
>> ----- Original Message -----
>> From: "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
>> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
>> Sent: Friday, April 11, 2008 5:08 AM
>> Subject: Re: [TenTec] Ten Tec 238A settings?
>>
>>
>>> Large variations in tuner settings from one end of 80M to the other end
>>> is
>>> normal. This is about typical of all tuners as the ratio of bandwidth to
>>> frequency is greater on the lower frequency bands than on higher
>>> bands/frequencies. I really haven't found a band or frequency or
>>> reasonable
>>> antenna below 30 MHz that the 238 tuner would not handle. {I've not
>>> tried
>>> to
>>> load a coat hanger. hi hi}
>>>
>>> I do have a chart based on settings for all bands and several settings
>>> vs.
>>> frequency for each band, and for two different antennas. This makes for
>>> quick tune-up when changing antennas or bands. I'll be glad to share
>>> that
>>> but it most likely would apply only to my antenna configurations, those
>>> being a 1/2 wave for 160M fed with balanced line and a 1/2 wave for 75M
>>> fed
>>> with coax.
>>>
>>> I do not suggest using a 4:1 balun for your configuration but a 1:1
>>> current
>>> balun. These are typically less lossy as you are not matching the feed
>>> line
>>> Z but the antenna load Z which is likely closer to 35 to 100 ohms or
>>> less.
>>> If you have an Antenna Analyzer measure the Z at the balun coax
>>> terminal.
>>> You'll likely find that it is 10 to 25 ohms. This being the case then a
>>> 1:1
>>> balun would be more nearly correct as the load with that configuration
>>> would
>>> be 40 to 75 ohms. Again, a better match for your coax between the balun
>>> and
>>> the tuner.
>>>
>>> For whatever reason, using balanced line of some 400 to 600 ohms, hams
>>> typically believe they should match the feedline Z. In actuality the
>>> feedline is more correctly reflecting the antenna feed impedance. And
>>> is
>>> some cases, acting like a transmission line transformer.
>>>
>>> Here is a case where a 4:1 balun is accurately used. The old fashion
>>> folded
>>> dipole made of twin lead. The feed Z of a 1/2 wave folded dipole where
>>> the
>>> top and bottom conductors are of equal size is nominally 300 ohms when
>>> greater than 1/4 wave above ground. Add an electrical 1/2 wave of
>>> feedline
>>> and one has an antenna with a feed impedance at the transmitter of about
>>> 300
>>> ohms. Use a 4:1 balun and the transmitter feed is 75 ohms showing a SWR
>>> of
>>> 1.5:1 . Drop the antenna down to less than 1/4 wave and the feed Z
>>> will
>>> drop toward 200 ohms which then with a 4:1 balun the feed point for the
>>> transmitter is now approaching 50 ohms.
>>>
>>> 73
>>> Bob, K4TAX
>>>
>>>
>>> ----- Original Message -----
>>> From: "Denton" <denton@oregontrail.net>
>>> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
>>> Sent: Friday, April 11, 2008 12:28 AM
>>> Subject: [TenTec] Ten Tec 238A settings?
>>>
>>>
>>>>I have a horizital loop up about 30' that has about 240' of wire in
>>>>roughly
>>>> a trapazoid shape....have found that by using a certain length of 600
>>>> ohm
>>>> feeders with a 4 to 1 balun, I have swr below 3.5 to 1 or below on all
>>>> bands
>>>> from 80 thru 10 meters, as measured at the balun's input...with the
>>>> exception of 17 and 60 meters. I am also using about 20 ft of good
>>>> quality
>>>> coax to the shack with a TT 238A tuner to take care of the minor swr on
>>>> the
>>>> system.
>>>> I notice that on 75 and 80 meters there is a large variation in tuner
>>>> settings from one end of the band to the other....is this typical of TT
>>>> tuners and L networks in general?
>>>> It appears to be a decent antenna system....if I can hear them, can
>>>> work
>>>> them.
>>>> I have also verified the antenna's effiectiveness by also using it with
>>>> a
>>>> link coupled transmatch...by extending the 600 ohm feeders and running
>>>> a
>>>> short stubb of 400 ohm line to the shack.
>>>> TT's L network gives me a much broader matching range, otherwise would
>>>> just
>>>> use the balanced transmatch.
>>>>
>>>>
>>>> _______________________________________________
>>>> TenTec mailing list
>>>> TenTec@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>>
>>>
>>>
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>
>>>
>>
>>
>> _______________________________________________
>> TenTec mailing list
>> TenTec@contesting.com
>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|