MARCH 2025 PRESENTATION

 

Slides by Dave Harris

Questions:  Email me at jushamn@gmail.com. Put CSERG on the subject line.

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ANTENNA DEFINED

• Antennas divert, direct, or concentrate RF energy in one or more directions.

This directional property is called GAIN.

The amount of gain is referred to as a number of dBi.

• Example 1.8 dBi

Or as a number of dBd.

• Example 2.3 dBd

You will sometimes see an antenna's gain stated in dB.

• This does not tell you anything useful about the antenna's gain.

dBi DEFINED

• Decibel gain referenced to an isotropic radiator
• Also referred to as a “point source”

ISOTROPIC RADIATOR

• A spherical point from which energy (RF) radiates equally in all directions.
• An infinitely small point in free space.

dBd DEFINED

• Decibel gain referenced to a dipole.
• A perfect dipole in free space.

DOUGHNUT SHAPE

• A dipole’s energy is diverted away from the ends and bulges in the middle by 2.15 dBi.
• Dipole in free space.

dBi vs dBd

• Gain (dBd) = Gain (dBi) – 2.15
• Gain (dBi) = Gain (dBd) + 2.15

ANTENNA COMPARISON

• Antenna A claims forward gain of 4.0 dBd
• Antenna B claims forward gain of 4.5 dBi

WHICH HAS THE MOST GAIN?

• First convert antenna A’s gain to dBi.

dBd to dBi

• To convert to dBi add 2.15 to antenna A’s dBd gain

CONVERT A’s GAIN TO dBi

• 4.0 dBd + 2.15 = 6.15 dBi
• Antenna A's gain in dBi is 6.15

A vs B

• 6.15 dBi (antenna A) – 4.5 dBi (antenna B) = 1.65 dBi
• Antenna A has 1.65 dBi more gain than antenna B

- -  Most of use think in terms of Watts or radiated power. Radiated power comes in two varieties. - -

ERP OR EIRP

• ERP – Effective Radiated Power (Assumed Effective Dipole Radiated Power)
• EIRP – Effective Isotropic Radiated Power

RADIATED POWER IN WATTS

• 1 Watt applied to each antenna’s feed point
• Antenna A’s ERP is 2.51 Watts or EIRP 4.12 Watts
• Antenna B’s ERP is 1.72 Watts or EIRP 2.82 Watts

NOTE!!!

• dBi and dBd apply ONLY to antennas.
• Coax, amplifiers, filters, attenuators, sound, etc use other forms of dB notation.
• Wikipedia lists 60 different dB notations for various disciplines.
• dBW, dBm, dBz, dBsm, dBhl, dBpp, dBvu, etc.

Links

 Power Calculator — db /Watts/ EIRP
https://www.qsl.net/v73ns/dbwcalc.html
Worth a look, includes VE ham license app
https://www.qsl.net/v73ns/
Another worth the look
https://m0ukd.com/calculators/

FINAL THOUGHT

• Anything metal is a potential antenna. It will radiate or reflect (re-radiate) your signal.
• Yes, Grundalclitch, even the bed springs.

XEIGU G90 OWNERS, UPDATE

 Johnny Rauzi send a link to a website that sells filters for broadcast interference and ham band bandpass filters. These are designed for QRP transceivers such as the Xeigu G90. 

Click on this link K9DP Shop

XEIGU G90 OWNERS, HEADS UP

 A friend Chazz, K7OVG, and I were talking about a problem with his Xeigu G90. I also talked with another ham having similar problem during Winter Field this year. Turns out they both have been experiencing interference when  strong out of band signals were present. In my friends case it was nearby AM broadcast stations. In the other case it was another nearby ham operating on a different band. This is most likely caused by overload of the first RF amplifier in the receiver.

My friend was able to solve the problem by using an external tuner between the G90 and the antenna to act as preselector. (I know, two tuner is supposed to be a bad idea, however, desperate times call for desperate measures.) Back in the "good ol' days", it was common practice to use a preselector ahead of a receiver to solve the same problem. These devices were tunable band pass filters. One would set the receiver to the band of interest, and next set the preselector to the same band and peak the desired signals.

 Chazz did the following with his G90. Selected the desired band and tuned the external tuner then pressed the tune button on the G90. He was able to stop the interference. He said he was able to transmit through both tuners without incident. 

Try using just the external tuner first to see if it solves the problem. If it does the don't use the internal tuner at all.

If you try this with a different transceiver, bypass the internal tuner while you tune the external tuner. Then engage the internal tuner and let it tune. This lets the external tuner match the 50 ohm input to the transmitter. Then the internal tuner sees a 50 ohm input and adjusts to match it. Now both tuner act as bandpass filter, preselector, ahead of the first RF amp.

Another solution is to purchase preselector. Be sure if you do that there are provisions to bypass the preselector while transmitting. I looked online and found several preselector options. Most of the ones I saw were designated for SDR receivers, however, there may be something out there that has built-in  transmit bypass capability.

If you try this, please let me know what you experienced. Send an email to k7pdw@arrl.net and put CSERG on the subject line.

[UtahVHFS] - Annual Swap Meet 29 March 2025

 The annual Utah VHF Society Swap Meet will be held on Saturday 29 March 2025 at the Western Sports Park (Formerly the Legacy Events Center) 1049 W Clark Ln, Farmington, UT 84025. This is the same location and building that we have used in the past. Parking is available in the main parking lot or at the east side to the building.

The doors open for set up at 0800 and selling begins at 0900. Members get into the event for free, nonmembers pay a $10.00 entry fee. Tables are $7.00. If you bring your own table a space is $5.00. We only have a limited number of chairs so bring one if you choose to. Sellers please come in and pay for your table before you bring your equipment in. We will have refreshments for sale if you desire, Sodas, coffee, hot chocolate, donuts and snacks.
At the conclusion of the event about 11:30 we will have a prize drawing for Society members in addition we will draw one prize for any member of the Society present or not, all other prizes will be presented to Society members present for the drawing.
We look forward to seeing you all at the Swap Meet.

MEETING SCHEDULE 2025

JAN 29 - LEE BARRETT  Determining The Impedance Of Unknown Coax

FEB 26 - BYRON HELLEWELL  Internet Radio Linking Project

MAR 26 - DAVE HARRIS  Comparing Antenna Gain Specifications

APR 30 - ART THOMASON DMR

MAY 28 - MICAH REDMOND Ham Radio Modes

JUN, JUL, & AUG - Summer Vacation

SEP 24 - TBD

OCT 29 - TBD

NOV 26 - Thanksgiving Eve, No Meeting

DEC 31 - New Year's Eve, No Meeting

Conductive Fabric Ground Plane

Conductive fabric is available from Amazon. It make an excellent ground plane in place of long copper wires. Several hams in the area have used this with Wolf River Antennas with great result. It's very light weight and flexible. It does tend to get blown about in windy conditions but following are a couple of solutions for that if rocks are not handy to hold it down

Solution 1 - Grommets

I found the cloth is so thin the grommets pulled out. So my XYL sewed in these upholstery reinforcements and I redid the grommets. I use fishing weights on carbineers to hold the cloth on the ground. Very fast setup and flattens out my SWR across the bands with my WRC and 17' whip. de KJ8MRH 

Solution 2 - Bias Tape Edging

I had my wife sew bias tape along the edges. She cut the tape several inches longer than the cloth then folded it back and stitched it to form a loop that could be used with stakes.

I have used this with my home brew 1/4 wave length vertical on 15 meters. I got S7 and better signal reports from Texas, Kansas, California, Virginia on SSB. Mat is only 42 X 58 which is fine for 15 meters and up. I'd recommend getting a larger piece if you plan to work on lower bands.

UPDATE: UPPING THE PERFORMANCE OF YOUR HT

Hi All

I ran some tests on tiger tails. I noticed in the video that he did not test a tiger tail with a rubber duck antenna. All the antennas he tested were quarter wave.

I decided to run some tests of my own. I have yet to do any field tests. I don't have an instrument to check field strength as he did in the video. 

I ran the tests using my NanoVNA.

First, I checked the SWR on 2 quarter wave whips and three rubber ducks. They were all under 2:1 SWR across the 2 meter band.

Second, I used one of the whips to tune a tiger tail made of #24 AWG magnet wire. It was necessary to use that small wire so the antenna could be screwed down all the way onto the radios, Baofeng UV-5R and Anytone AT-878UV. They both have recessed antenna connections. I was able to trim the tiger tail back to the same SWR that the whip showed without the tiger tail. 

Third, I proceeded to check the second whip. It's SWR with and without the tiger tail was also nearly the same. It did show a slight shift upward in frequency with the tiger tail. However, the SWR was still well under 2:1 across the band.

Fourth, I tested the rubber ducks with  the same tiger tail. In every case the SWR was effected so that most of the 2 meter band was higher than 2:1 SWR. One was higher than 2:1 across the entire band.

Fifth, I tried to build another tiger tail that would work with the rubber ducks. Every attempt resulted in no better SWR than the original tiger tail that I tuned with the quarter whip.

My conclusion is that tiger tails have the potential to improve a HT's performance with a quarter wave whip. As far a with a rubber duck it does not look too promising.

Come spring and better weather, I plan to run some field tests with another ham. I've yet to determine what that test will look like. But as a minimum there will be a receiver with a S-meter for making the measurements.

73,

Dave, K7PDW

Keep On Ham'n

PS: I had intended to post this much earlier but life intervened. The field test have yet to be performed either.