Recent posts

Pages 1 ... 8 9 10
91
Antennas / Re: Effect of Ground for Short...
Last post by bobtennis - January 04, 2020, 05:44:59 am
I'll bet the rats at the stream found the results of your experiment simply shocking!
92
Antennas / Re: Antenna wire
Last post by bobtennis - January 04, 2020, 05:18:31 am
Winding on a stick or folding wire back on itself will get you ballpark measurements, but may require a lot of extra trial and error testing after cutting the wire. These methods can induce capacitance or inductive loading effects which may skew measurements.

One alternate method I used, and it worked really well, is to take a reading of the lowest SWR point at your initial wire length and note that frequency. You can use the standard 468/frequency to determine an initial length.

Multiply the initial length times the lowest measured SWR frequency (i.e., take test measurements) to find an adjustment factor, then calculate adjusted length using this factor for best resonance (SWR) at your desired frequency. You can use this method whether you have an antenna analyzer or multiple trial measurements, as long as you can measure lowest SWR point (but the analyzer makes this really easy!)

Restated:
original length x original frequency low SWR point  = adjustment factor; then divide the desired frequency into this factor to get the corrected length.

For a hypothetical example:
Given - Initial trial length of 34 ft per dipole antenna leg, and desired 40m frequency is 7.100 mhz.

If measured low SWR for initial length of 34 ft antenna leg is at a frequency of 7.00 mhz, to find the length needed 7.100 mhz, set up the equation:

34 ft x 7.0 mhz = 238 (new adjustment factor) :  new adjustment factor 238 / 7.100 mhz = 33.5 ft new length (or 33 ft, 6 in - remember to convert the decimal to inches!).

This should get you very close to the correct length, and, it also takes into account your particular circumstances which cause a deviation from using the standard formula 468/freq mhz (or 234/freq for each dipole leg), such as surroundings, height, and other factor affecting antenna resonance.

Metric system users will need to make appropriate adjustments in lengths and calculation formulas.

Although this example used a dipole for illustration, there is no reason not to use it for other type antenna adjustments. For example, I used it to adjust a single leg sloper coming off a rooftop tower counterpoise successfully. It really just boils down to using a math tool to calculate a proportionate change.
93
Antennas / Re: End fed windom
Last post by Sig Man - January 03, 2020, 01:18:57 pm
Made one yesterday, used rg-174 for portable use. First attemp gave vswr 1.4 on 3.550, good on 7.050 and around 5 on 60m (the kx3 tuner will fix that).
Waiting for the snowstorm to end, so i can do a rx/tx test
94
Antennas / Re: End fed windom
Last post by Oliver - January 03, 2020, 09:39:40 am
Well Gil, the antenna is not that complicated to build as you see at the swedish PDF.

The advantages cannot be denied.
No tuner needed and you don´t have to care about ground connection.
The only disadvantage is the missing 30 and 15 Meter match.
95
General Discussion / Re: Encryption
Last post by gil - January 03, 2020, 05:46:45 am
Some DMR handheld radios have built-in encryption, like the TYT MD-680.

Gil.
96
Digital Modes / Re: Sound Card Interface
Last post by gil - January 03, 2020, 05:45:19 am
Hello. I use the Mini PRO SC, so far no problems, but I don't use digital modes much...

Gil.
97
Antennas / Re: End fed windom
Last post by gil - January 03, 2020, 05:44:05 am
This antenna seems overly complicated compared to a simple 49:1 or 64:1 transformer...

Gil.
98
CB / Re: Is it wise to buy a CB
Last post by Oliver - January 02, 2020, 05:19:02 pm
"Is it wise to buy a CB"

Definitely yes!
They are cheap to get and make you a easy communication backup.
A brand new set radio and magnet car antenna is unter 100 $ or €.
That is what i have in my car EDC:
https://www.amazon.de/dp/B07BR1133G/ref=cm_sw_em_r_mt_dp_U_4zMdEb3R1T1S5

A set like this will give you a good chance to get help everywere.
Together with a car battery you are totally independent.
In a shtf case it could be more helpful than a HAM setup.

Interesting Fact:
Here in Germany they fear a power blackout.
We had some issues in the past. (long story)
Now they want the Radioamateurs for backup.
The main job will be the connection between the citizens and the authorities.
But also the monitoring of the CB frequencies is being considered.
Thats because CB is still wide spreaded.
99
CB / Re: Is it wise to buy a CB
Last post by tline - January 02, 2020, 04:31:18 pm

I hooked my cb up to an end fed 40 and was happily surprised when it seemed to work pretty good.


Quote from: gil on December 26, 2019, 09:05:46 amIt certainly isn't what it used to be... A half-wave end-fed wire with a 49:1 transformer would be the best antenna for CB IMHO. Height is your friend for local comms...
Gil.
100
Antennas / Re: End fed windom
Last post by Oliver - January 02, 2020, 04:27:52 pm
Hi Sig Man!
I am using that antenna/antenna style.
They are often called city windom antenna, because you just need one pole.
This can be a tree or a other house or whatever.

My is produced by:
https://www.radial.ru/catalog/antennas/dipole/windom6/eng/
The german importer is Wimo.

Its an exellent antenna.
I using it on 80 Meter a lot in FT8.
The reports i get are allways very good.
Most of the bands you don´t even need a tuner.
The build-in TXR tuners does the job anyhow.
These type of antenna will be also very good for fielddays or short time use.
(Oh yes it would be a solution for Gil)
My antenne came with a nice bag and has a exellent quality!

You see the rick on my qrz.com site.

73 de DO1OH
Oliver
Pages 1 ... 8 9 10