`For ease of adjustment I found that it is necessary to mount a gear for variable air capacitors.`

SWR graph - 7050 +/_ 50khz Resonant frequency = 7071 khz Bw (swr<1.5 = 268 khz) Bw (swr<2 = 484 khz )

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# Category: Uncategorized

## Hairpn modified antenna for 40 m band – improvments and updates (h=5.5 m above the ground)

## Hairpin modified antenna – estimated performance based on WSPR data analyse

## 40 m band – Hairpin antenna – Theme with variations (part 2 of previous article)

## New type of shortened antenna for 40 meters band – part 1 – Light version

## FEF-CMMHQCCBA&T (Front end filter comutable multi-monocrystal for heavy qrm conditions, connected between antenna and transceiver)

**Note 1.**
**Note 2.**
**Note 3.**
**General note**
**How to adjust the FEF (Front End Filter)**
** **
## 2018/2019 contest activities

`For ease of adjustment I found that it is necessary to mount a gear for variable air capacitors.`

SWR graph - 7050 +/_ 50khz Resonant frequency = 7071 khz Bw (swr<1.5 = 268 khz) Bw (swr<2 = 484 khz )

So, we have an short antenna, easy to build and install. It was working in WSPR mode more than 3 days. It’s time to find the performances… and to see if our expectations are to big, or what can we improve.

First analyse is a simple one. Just go to VK7JJ site (http://wsprd.vk7jj.com/) and follow the instructions. You can see when you see a lot of useful informations about your antenna, the antenna location and propagation.

It looks fine… it’s only an example of useful info. But is not enough. The chart say you can work from YO stations from VK, JA, North and South America. Yes, using WSPR mode.

What about other modes ?

Let’s go to KP4MD site (https://www.qsl.net/kp4md/wsprmodes.htm#application) and download the mode-comparison excel file.

Using your WSPR data you can find if you can work a specific station in another mode (CW, RTTY, SSB, etc.).

Let start with the bad news…

After you shall download and process the data, you shall find that the probability to work VK7JJ in RTTY or SSB mode is very low to very, very low. Red colour is not good….

Let’s check other DX stations

Sorry, no K1ABK, no JA5NVN.

OK, dont panique, let see what can we work.

TF4X 3927 km

MM7BWK 2544 km

OH3FR 1867 km

So, if you want more, try to find if you can use a higher position or re-locate the position, or improve soil parameters, etc.

For example, my location is very unfriendly regarding the obstructions around me. As you can see in the graphs (from 1st part, VK7JJ site), the existing freeway to 310 degrees azimuth is confirmed by number of spots and the obstruction from 230 degrees (a new big house, etc.) is also confirmed by no data/spots on that direction.

After 2 weeks of testing the Hairpin antenna for 40 m band (the light model with Cu wires), it’s time to build the regular prototype with Al tubes. But, first off all, let’s play with MMANA- GAL to see what are the limits.

The main differences between classic Hairpin antenna and this model are:

- The antenna is mounted on a metalic grounded mast.
- The spacing between arms is larger to obtain a wider antenna

Now, let’s play with parameters.

__Spacing__

Aluminium tube diameter = 24 mm

Hairpin length = 3 meters

Height from the ground = 4 meters

Ground setup = 14 / 5

Q capacitors = 500

R =50 ohms (+/- 1)

jX = -1 /+1 ohms

**Higher spacer, better gain and Bw**

__2. Aluminium tube diameter__

Spacing = 24 cm

Height from the ground = 4 meters

Hairpin length = 3 meters

Ground setup = 14 / 5

Q capacitors = 500

R =50 ohms (+/- 1)

jX = -1 /+1 ohms

**Higher tubes diameter, better gain and Bw**

__3. Q capacitor__

Spacing = 24 cm

Height from the ground = 4 meters

Hairpin length = 3 meters

Ground setup = 14 / 5

Aluminium tube diameter = 24 mm

R =50 ohms (+/- 1)

jX = -1 /+1 ohms

**Vacuum capacitor (High Q), high gain but narrow Bw**

**Regular air capacitors, lower gain but wider Bw**

__4. Height from the ground (grounded mast length)__

Spacing = 24 cm

Q cap = 200

Hairpin length = 3 meters

Ground setup = 14 / 5

Aluminium tube diameter = 24 mm

R =50 ohms (+/- 1)

jX = -1 /+1 ohms

**More height, more gain and Bw**

__5. Hairpin length__

Spacing = 24 cm

Q cap = 200

Ground setup = 14 / 5

Aluminium tube diameter = 24 mm

R =50 ohms (+/- 1)

jX = -1 /+1 ohms

Height = 4 meters

**Too short, less gain. Too long, you can not tune the antenna (value of Cv1 will drop to parasitic capacity, or to zero)**

Why this antenna has no name ? I dont know… I dont know exactly what kind of antenna is this (….hmm, I know, is a variant of magnetic antenna, is using the parallel line inductance, etc, etc, etc. is the same setup when you need to find Qf for a capacitor).

So, let’s see how was borned. Few weeks ago, a heavy storm distroyed my telescopic mast and the 40 m band delta loop, so I need something for a small yard, with a lot of higher obstructions around me, with a limited telescopic mast (max. 6 m), etc. The hamradio nightmare !

I tried to design a magnetic loop… to narrow for rtty contest… too large if you need a good efficiency (2.4 meters diameter…). But, I found something in Mmana library, named HAIRPIN magnetic antenna. It looks nice, but still to narrow.

it looks friendly, like this

but the swr chart, wasnt friendly…

So, I’ve started to play with dimensions, diametres, etc. After one week of simulations the result was something like this:

- a parallel line of 2.6 metres lenght with 24 cm spacing, shorted at upper side
- 2mm diametre Cu wire
- 4 meters up from the ground
- Two air variable capacitors (max. 100 pF each)

This is the theoretical model

The real world shows something different

As you can see, the practical prototype has a larger Bw, aprox. 75 kHz for SWR < 1,5. Why this difference, from 22,5 khz to 75 khz ? Because in simulation I didnt complete the Qf for capacitors.

If we are playing with Qf, we can find a value when the two charts are matching

7000-7100 khz / Practical model

7000-7100 khz / Theoretical model

7000-7200 khz / Practical model

7000-7200 / Theoretical model

So, starting this point, we can assume the simulation match the practical model.

Preliminar traffic results -WSPR (200 mW)

and some pictures from prototype

And schematics

Next part will be with Heavy version, more commercial aspect (I hope), with proper capacitors and better gain.

Any questions, dont hesitate to send mail: cristian.moldovanu@gmail.com

Many times, during rtty contests, I have a big problem with qrm. A lot of strong signals in a small bandpass, so, if you reduce the RF Rx gain or connect the 6-12 dB attenuator you shall loose the weak signals. In fact, the receiver (the preamplifier, mixer, etc) have to deal with a lot of unwanted (by the operator) signals, so the transceiver performance will be degradaded. Usualy, the modern transceiver have a quality FEF (Front End Filter) after the 1’st mixer. It’s wonderfull, but still need to reduce the RF Rx gaind during some periods of the contests.

So, last cqwwrttycontest (2020) I tried an old solution, a FEF connected direct between antenna and transceiver, with 5 comutabloe monocrystals (7041, 7045, 7055, 7070 and 7082 kHz.).

Few explanations: circuits A & B give us the posibility to have a small variable bandwidth; circuit C is a simple one, with the minimum bandwidth obtainable from a specific crystal. A short theory lesson for the “C” configuration we can find at page 106 of The Radio Amateurs Handbook – 14th edition.

And now, others people experience:

(http://eddystoneusergroup.org.uk/Restoration%20projects/Tech%20Short%205%20-%20Receiver%20Selectivity%20and%20Crystal%20Filters.pdf)

and M0AYF QRSS band pass filter

Even you know the Fs of a crystal can be modified with a C in series, you shall find that the RL, or selectivity is depending how far you are from Fs. So, for a crystal with Fs= 7045 khz,** the optimal aria for this kind of filter is very close from Fs, only 1 khz up and down** (even you can move Fs with 5-6 khz up, with Cv=5-10 pF). The explanation is Q factor wich is degradeding when you modify Fs.

Ct have to be a good trimer, air or mica, with small capacity. Dont forget that you have to adjust somewhere around 3-5 pF, exact the value of crystal Cp.

Find a good variable rezistor, with a very low rezidual inductance.

Take care of practical setup: minimum wires, short wires, screening. If you can not adjust Ct for a good diagram, it seems you have parasitic capacitance in circuit, wich are greater than your Ct. Also, dont forget you need another module, the relais module. You need to disconect the FEF during Tx, to bypass the FEF and you are not using him, etc. You need minimum 3 good relais: the antenna connector, the transceiver connector and the relais for commanding those 2 relais. The circuit depends what transceiver you are using, etc.

My first prototype: only 2 crystals, and a toroidal transformer on the output, to transceiver.

The adjustment is done with a RigExpert analyzer (AA-230 Zoom): 1st step adjusting the SWR for the lowest value (in the bandpass), and after that checking the whole diagram for RL (returning loss). If the value is more than 30 db, is OK (dont forget, 1 S point = 6dB, so 30 dB = 5 S points attenuation for unwanted signals).

Actual prototype has 5 crystals, a plastic box with aluminium tape for screening and a variable rezistor replacing the second toroidal transformer. It was not my best day when I put everything inside…. but I promise (to me) to build a more adequate aluminium box for cqwpxrtty contest.

Dont forget to adjust also the rezistor for a minimum SWR. Depending your crystals and setup you can obtain RL up to 50 dB.

… hmmm… I am litle shame of my presentation, I dont know if you understand what is in last 2 pictures, but the device is working.

How to use ? Very simple. Connect the device inline, put on BYPASS, and when have the biggest QRM around a frequency where you have crystals inside, connect the unit and try the Cv for an optimum Rx. Also, dont forget the RX RF gain, because nothing is an ideal solution.

So, thank you for your attention, and do not hesitate to ask if you need more info.

Good luck in contest (and QRM),

YO4DFT – Cristian

cristian.moldovanu@gmail.com

P.S.

2 crops from my log, when I used FEF to deal with QRM.

………………

QSO: 7071 RY 2020-09-26 1530 YO4DFT 599 20 DX RV3ZN 599 16 DX

QSO: 7070 RY 2020-09-26 1533 YO4DFT 599 20 DX LY3CY 599 15 DX

QSO: 7069 RY 2020-09-26 1537 YO4DFT 599 20 DX JH4UTP 599 25 DX

QSO: 7069 RY 2020-09-26 1538 YO4DFT 599 20 DX S57X 599 15 DX

QSO: 7069 RY 2020-09-26 1540 YO4DFT 599 20 DX SP2UU 599 15 DX

QSO: 7069 RY 2020-09-26 1541 YO4DFT 599 20 DX YL2BR 599 15 DX

QSO: 7069 RY 2020-09-26 1541 YO4DFT 599 20 DX UY7MM 599 16 DX

QSO: 7069 RY 2020-09-26 1542 YO4DFT 599 20 DX DA2X 599 14 DX

QSO: 7069 RY 2020-09-26 1543 YO4DFT 599 20 DX LY9Y 599 15 DX

QSO: 7069 RY 2020-09-26 1543 YO4DFT 599 20 DX RA3TT 599 16 DX

QSO: 7069 RY 2020-09-26 1543 YO4DFT 599 20 DX YL3CU 599 15 DX

QSO: 7069 RY 2020-09-26 1544 YO4DFT 599 20 DX SM5MX 599 14 DX

QSO: 7069 RY 2020-09-26 1545 YO4DFT 599 20 DX OK5NW 599 15 DX

QSO: 7069 RY 2020-09-26 1548 YO4DFT 599 20 DX IT9RBW 599 15 DX

QSO: 7068 RY 2020-09-26 1549 YO4DFT 599 20 DX IZ3BUR 599 15 DX

…………………..

QSO: 7040 RY 2020-09-26 2144 YO4DFT 599 20 DX DH8BQA 599 14 DX

QSO: 7040 RY 2020-09-26 2145 YO4DFT 599 20 DX LA2XNA 599 14 DX

QSO: 7040 RY 2020-09-26 2147 YO4DFT 599 20 DX OH1SIC 599 15 DX

QSO: 7040 RY 2020-09-26 2148 YO4DFT 599 20 DX PA3BFH 599 14 DX

QSO: 7040 RY 2020-09-26 2148 YO4DFT 599 20 DX PB7Z 599 14 DX

QSO: 7040 RY 2020-09-26 2149 YO4DFT 599 20 DX DF2RG 599 14 DX

QSO: 7040 RY 2020-09-26 2150 YO4DFT 599 20 DX IU2LTO 599 15 DX

QSO: 7040 RY 2020-09-26 2151 YO4DFT 599 20 DX DJ1OJ 599 14 DX

QSO: 7040 RY 2020-09-26 2151 YO4DFT 599 20 DX UV5EDW 599 16 DX

QSO: 7040 RY 2020-09-26 2152 YO4DFT 599 20 DX IU4HRJ 599 15 DX

QSO: 7040 RY 2020-09-26 2153 YO4DFT 599 20 DX DL3SYA 599 14 DX

QSO: 7040 RY 2020-09-26 2155 YO4DFT 599 20 DX DL5ARM 599 14 DX

QSO: 7040 RY 2020-09-26 2155 YO4DFT 599 20 DX OZ1OXQ 599 14 DX

QSO: 7040 RY 2020-09-26 2156 YO4DFT 599 20 DX DM1FS 599 14 DX

QSO: 7040 RY 2020-09-26 2156 YO4DFT 599 20 DX R6CC 599 16 DX

QSO: 7040 RY 2020-09-26 2157 YO4DFT 599 20 DX DL3KUD 599 14 DX

QSO: 7040 RY 2020-09-26 2157 YO4DFT 599 20 DX DL4ME 599 14 DX

QSO: 7040 RY 2020-09-26 2158 YO4DFT 599 20 DX PA1JM 599 14 DX

QSO: 7040 RY 2020-09-26 2200 YO4DFT 599 20 DX DL0BI 599 14 DX

QSO: 7040 RY 2020-09-26 2201 YO4DFT 599 20 DX IU2CIQ 599 15 DX

QSO: 7040 RY 2020-09-26 2204 YO4DFT 599 20 DX IK1BPL 599 15 DX

QSO: 7040 RY 2020-09-26 2206 YO4DFT 599 20 DX SQ3MZ 599 15 DX

QSO: 7040 RY 2020-09-26 2206 YO4DFT 599 20 DX DQ9Y 599 14 DX

QSO: 7040 RY 2020-09-26 2208 YO4DFT 599 20 DX DL6UAA 599 14 DX

………………….