R8 HF Vertical

(http://www.lairdtech.com/)

Recently I picked up a second hand Cushcraft R8 vertical.

I had the folliwing goals in mind

1. Vertical
2. Multiband
3. No radials
4. Low take off angle
5. WARC bands included
6. Possibility of field day operation
   

• Vertical

Given the layout of the my house's lot, a second antenna would be easier to install if it were a vertical. Also my existing antenna is a 80M to 6M Windom Buxcomm model 802136 and I am intersted in having a vertical to compare. I'll likely never setup a beam so this second antenna will be it.

• Multiband

Multiband is tablestakes, because I need to able to get as much out of an antenna as I can. The R8 is one among very few 8-banders covering from 40 to 6m, WARC included.

• No radials

I like the idea of no radials, mainly because of the ease of installation and flexibility of installation lacation. R8 uses 7 49in stainless radial rods at the base of the antenna.

• Gain and Low take off angle

DX, DX, DX, Low take off angle is important for DX work. With its low radiation angle R-8 vertical should have distinct advantages compared to my windom. The 360 degree coverage should be nice as well.

• Power Handling

The R8 supports 1500W which is plenty for my FT2000D which is a 200W rig.

• WARC bands included

I enjoy digital operation and I often find that the WARC bands have activity, but the Windom antenna does not tune up on 30m for example.

• Possibility of field day operation

The R8 could be used in field day operations but due to its weight it is not easy to get it down without help. Once installed, I think its up there for the long run.

Considerations

• Guying
  

I did guy the antenna down to three points.

• Grounding

I have grounded the mast to a single 8ft ground rod with a run 10ft run of #6 ground wire.

Specifications

Model R8
Gain, dBi 3
Height, m. 8.7
Horizontal rad, deg 360
Power Rating, Watts CW 1500
Vertical Radiation Angle, deg. 16
Band / Bandwidth (kHz) 10m >1500
Band / Bandwidth (kHz) 12m >100
Band / Bandwidth (kHz) 15m >450
Band / Bandwidth (kHz) 17m >100
Band / Bandwidth (kHz) 20m >350
Band / Bandwidth (kHz) 30m >50
Band / Bandwidth (kHz) 40m >150
Band / Bandwidth (kHz) 6m >1500
VSWR at resonance (typical) 1.3:1
Weight, kg. 10.5
Wind Survival kph. 120

The Cleanup

Since the antenna was second hand I had quite a time cleaning up the antenna and setting all the element lengths to the specification.

• I cleaned up external surfaces with a combination of steel wool and lots of work. With this I was able to restore the antenna to showroom look, shine and all.

• The short 6" terminal tuning stubs rods were oxidized such that it was impossible to remove these from the longer stub tubes. I did confirm that all stubs were all stuck in place at the right lengths.
  

• I opened the R8 matching network box and confirmed that there were no mechanical failures of the components inside. A mechanical inspection was complete.
  

• I completely assembled the antenna indoors to see the antenna fit together and confirmed nothing was mechanically broken or missing.

Installation Preparation

• I decided to install the vertical on the corner of my backyard shed. A 2 in pipe was installed up through the roof of the shed.
  
• I decided to guy the antenna from the initial start
• I placed a 1:1 choke at (near) the antenna.
  
• Grounding, 8ft copper clad steel rod at base of mast
  
• Feed line, was 100ft RG/8
  
• Lightning arresor, was placed at the house

Operation

• All bands tune up and better than 1.5:1 on all but the high end of 40m.
  
• Have not tried to see how it tunes on 6m.

RSQ and PSK

A recent look into my own signal quality on PSK made me take a search on the net for information on PSK signal quality.

I came upon this web site (link) which is a site concerned with

"This site is devoted to promoting RSQ as an improved signal reporting system for narrow band digital modes and to demonstrating its application to the popular PSK31 mode."

To this end, they recommend and point out that Regions 1 and 3 have adopted the following

Readability (% of text)
R5 95%+ Perfectly readable
R4 80% Practically no difficulty, occasional missed characters
R3 40% Considerable difficulty, many missed characters
R2 20% Occasional words distinguishable
R1 0% Undecipherable

Strength
S9 Very strong trace
S7 Strong trace
S5 Moderate trace
S3 Weak trace
S1 Barely perceptible trace

Quality
Q9 Clean signal, no visible sidebar pairs
Q7 One barely visible pair
Q5 One easily visible pair
Q3 Multiple visible pairs
Q1 Splatter over much of the spectrum

Seems very reasonable to me and will become part of my operating practices.

PSK Splatter solved

While operating PSK on 20m this morning I received a report that I was splattering across the band. With this in mind I though I should look into this.

I was not operating outside my normal situation.

FT2000D
30W - 80W depending on the QSO
Signallink USB
HP PC
only have 1 antenna, the Windom

Let the experiment begin.

Not knowing how bad the problem was, I went up to 18.1MHz to find a quiet place to poke around.

The only station I saw on the band was a fellow operator here in Ottawa, VE3OIJ. We transmitted back and forth a bit and found nothing remarkable. Leading me to think nothing is seriously broken.

I wanted to see my own signal, so I used the IC7000 to receive the tx output of the FT2000D

Rig
TRX - FT2000D
Freq - 18.1MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz

SignalLink
Tx - 3/10

Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB

Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??

At 6dB/S-unit, if my fundamental was received at his station at S9, then this "splatter" would be received at -S2, i.e. 2 S-units below, S0, these cannot possibly be the splatter my fellow operator saw.


VE3OIJ was able to see these terms, but we are less than 10km apart. It may make sense to follow these terms a bit more. The plot below shows my signal from 1W to 150W into my dummy load. In all cases the relative size of the "splatter" remained fixed. This tells me that these terms are not being generated by the radio's linearity ans regardless of my transmit power would not be a problem to any one but an operator in my city.


How to get gid of these? Don't know.

Next step was to try back on frequency, in case it was RF feedback into the shack that only happens on 20m.

Rig
TRX - FT2000D
Freq - 14.070MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz

SignalLink
Tx - 3/10

Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB

Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??


Identical results.

Below is a typical waterfall on 20m, "strong" signals are 30dB above the noise floor. If anyone else had terms like the ones above in their transmit signals there is no way I would ever see or be concerned with them.



Summary

I cannot improve the relative power in these terms by adjusting my TX power, as they go dB for dB with my fundamental signal.

Only someone in my local area will see these signals as significant, and the operator who indicated I was splattering did not leave his call so I can not tell. I should has asked, but I did not, a short QSO may have been a better idea.

For now I'll assume every thing is ok and go back to having fun.

Update:

Here is another plot of my tx signal.


Update #2

I was in a QSO with a Spanish station and received a 575 report, so again I thought something must be wrong. A plot of my transmit signal is below.

This time I recognized that the "regrowth" was at N times 120Hz, pointing me to a power problem. Also, I though I'd take a look at my CW output as a means to remove the PSK hardware and software from the equation. Below is my CW plot, this was for 10W output.


In my shack I power my table from two power bars. One regular power bar for all the ordinary stuff, PC, lamp, monitors, and a filtered power bar for the FT2000D, DMU2000, and the Kenwood PS-53 for the IC-7000 and / or TS-850. Both power bars are powered from the same wall outlet which has a dedicated 15A circuit for the sta

I can see in the plot above, that the same N*120Hz side tones are present, the first pair are only 35dB down.

Below is a plot of the same CW transmission when the FT2000D + DMU2000 and Kenwood PS-53 supply are on the same power bar as the rest of the shack. (avoiding the MFJ power

I can see in the plot below, that only the first 120Hz side tones are present, but now are 60dB down, a 25dB improvement. The MFJ-1164B power bar will need some further investigation.


In the meantime, returning to PSK mode, below shows a much improved transmit signal.

Rig
TRX - FT2000D
Freq - 18.10MHZ
Tx Power - 130W (by the FT2000D meter, just for testing)

Excellent.



Now I think I have a very good idea of how clean the PSK signal should be from my radio and will keep an eye.

Summary:

1) If you have an extra radio and Signallink you can run 2 copies of DM780 and see your own transmit signal. Grounding the second rig's antenna input will enable enough signal in to be detected.

2) Your AC supply should be suspected if you have N*120Hz sidebands

3) Read an understand how volume controls should be set for your software and PSK interface hardware

4) Looking at your CW output can help isolate the problem

5) a good transmit signal will have better than 25dB IMD, better than 25dB SNR and 60 to 70dB spurious free range.

All for now.