NMO34 with the W640 (64" whip) vs NMO-27 vs CWB-27

[RFI-EMI-GUY]

I'm anxious to see the of this but given the CWB is unobtainable for the most part, most of us will just have to fantasize about getting one, one day maybe a yard sale or eBay. Please keep us posted.

I for one am going to keep looking. On the other hand I wonder if the network components required could be retrofitted inside of a stock NMO-27?

 

[K9KLC]

I for one am going to keep looking. On the other hand I wonder if the network components required could be retrofitted inside of a stock NMO-27?

Ya, I'm going to continue looking but also not holding my breath. Also, I am going to really wait till the results of the test are in. I want to see the difference between those two. Hopefully it will be worth even looking for!

 

[RFI-EMI-GUY]

Ya, I'm going to continue looking but also not holding my breath. Also, I am going to really wait till the results of the test are in. I want to see the difference between those two. Hopefully it will be worth even looking for!

Yeah same here. My options are doubling up on antennas or whips as was suggested. It would be nice to have one antenna because I am not planning on having the 27-28 bands operational on both my CB and LB SYNTOR X9000 at same time to avoid RX front end overload. That would be accomplished by a coax relay and some electrical interlock.

 

[WSAC829]

Try a peak reading wattmeter on a modern HF amateur rig. With the radio set for about 20-25W carrier it should show 80-100W at full modulation

You do realize most “modern” HF rigs like the 7300 are limited to 25 watts on AM right? Of course they wont swing if you set the dead key to its AM max of 25 watts. Drop the AM power down to 5 watts, then watch it swing.

Like i said, the G90 wont win any DX contests on AM, but it's more than adequate to hold a conversation, and better sounding than most HF rigs on the current market. Just drop the AM power down on it to get decent AM audio.

 

[prcguy]

You do realize most “modern” HF rigs like the 7300 are limited to 25 watts on AM right? Of course they wont swing if you set the dead key to its AM max of 25 watts. Drop the AM power down to 5 watts, then watch it swing.

Like i said, the G90 wont win any DX contests on AM, but it's more than adequate to hold a conversation, and better sounding than most HF rigs on the current market. Just drop the AM power down on it to get decent AM audio.

25 watt carrier is the exact level to produce 100 watt peak at 100% AM modulation. You do know there is a 6dB or 4X increase from carrier to 100% modulation, don't you? You do know a 4 watt carrier on a CB radio produces 12 watts peak at 100% modulation, don't you? A 7300 is supposed to produce 100 watts peak when set for 25 watt carrier and so does just about any HF ham rig. But they sound like doo doo compared to an actual CB on AM.

 

[WSAC829]

As per the 7300’s manual:

• Output power: 100 W (Adjustable 5-100 Watts) SSB/CW/FM (AM: 25W - Adjustable 5-25 Watts)

You wont get 100 watts out of a 7300 on AM. Period.

 

[prcguy]

As per the 7300’s manual:

• Output power: 100 W (Adjustable 5-100 Watts) SSB/CW/FM (AM: 25W - Adjustable 5-25 Watts)

You wont get 100 watts out of a 7300 on AM. Period.

The 5-25w is carrier power, with modulation you will get much more. Maybe not exactly 100w but more. I'll measure peak AM power tomorrow on my Icom 7610 and some other amateur radios.

 

[K9KLC]

I'll measure peak AM power tomorrow on my Icom 7610 and some other amateur radios.

Since you're going to go thru the trouble to do this, could you check it at some other carrier levels? Maybe 5-10-15 & 25? You know inquiring minds want to know.

Truthfully it's been some years since I took any AM talking on a "ham type" radio seriously. My FT-450 sounds "ok" or so I'm told when I dial that down to about 15 watts but I've never checked it. I've never tried it (am) on the 991A or my 1000 D. Other radios thru out the years when I was trying that a little more seriously on AM were the Alinco DX-70 (worked well on 10 watts carrier) and the Kenwood TS 50 (again way way better on low) and the FT-100 Yeasu when I ran that in a more local delivery truck concentrating more on 20 and 40 meters but occasionally stopping and putting the RM -11S on the stick just to see what was going on if I was stopped already in traffic. Again, all of those were used on lower power settings not high in AM.

Other radios even dating back to hybrid or more full tube types worked at least some better on AM but all required to be set up for it. Even my Drake TR-4 didn't excel there but it would talk there. I guess, out of all of them, unless you count the Collins 32V2 which I only had possession of for a several months in the earlier 90's, the FT-101 Yaesu did ok when properly set up and using a D-104 Microphone.
Pretty much since solid state at least trying to get AM to work on any more modern rig, was just a lot of effort and time. There's mods out there to get some of these to work better, and I hear some guys down on the AM stuff on 80 and 40 occasionally running them but the guys that sound GREAT are usually running tubes and ancient stuff, and for a reason.

 

[WSAC829]

I'll measure peak AM power tomorrow

I’d be interested in the results. I never got more than 35 watts AM out of my 7300 when i had it.

Now as for AM audio on HF rigs… here is a snippet i recorded on my X6100 of my Alinco DX-SR8T. It’s a very bare bones rig with RF power selections of 1, 10, 50 and 100w for FM/SSB/CW and 1, 10, and 40w for AM. I set it for 10w carrier on AM and it swings just under 50w on AM. Nice crisp punchy audio.

P.S. Dont mind the slight hum in the audio. I couldn’t space the rigs out far enough to avoid it.

 

[K6GBW]

Alrightly gang, the testing is done. prcguy will post results when he can. It was interesting!

 

[prcguy]

Yes, we did some testing, probably need to do more testing, and had a great time. The test setup was K6GBWs vehicle as the transmit site with a modified NMO mag mount with magnetic coupling capacitor and RF choke in the feedline. Transmit radio was an Anytone 5555N II with an AC power supply to provide consistent power, then transmitter into a 6dB attenuator to provide a constant match then coax to the NMO mag mount. Antennas tested were an older Larsen NMO27 with ribbed base coil and a late model Laird CW27 broad band.

Receive site was my truck about 50yds away with Laird (Antenex) CW27 as the receive antenna (cuz I got so many) into an HP/Agilent 8562A spectrum analyzer initially then vehicle power problems forced me to use a TinySA Ultra spectrum analyzer. In both cases a peak search with cursor was used to find maximum signal level from the transmit site.

Receive site signal to noise ratio was huge, on the order of 50dB or more. The goal was to test receive levels with each antenna from the transmit site then repeat testing to prove the results are repeatable. The results with HP spectrum analyzer were not due to power problems leaving the TinySA Ultra as the only test instrument. A frequency of 27.200MHz was used for all testing being roughly in the middle of the CB band.

With that here are received signal levels from the TinySA first round:

Larsen NMO27 -9.9dBm
Laird CW27 -7.9dBm

Difference = 2dB with Laird showing more gain.

Round two:
Larsen NMO27 -9.8dBm
Laird CW27 -7.8dBm

Difference = 2dB with Laird showing more gain.

I then tested the TinySA Ultra with an HP8920 service monitor generating a signal in the -9dBm range similar to the antenna test setup then varying it a few dB to see if the TinySA tracks and it appears the TinySA level can toggle up to .5dB randomly but only in one direction, so the results can be skewed down by at least .5dB. Each measurement can be very close or off by at least -.5dB. I really wish the big spectrum analyzer did not have power problems as its much more accurate.

Next we measured the VSWR of each antenna using an Anritsu MT8212B Site Master calibrated with short, open and load on the spot from 25 to 32MHz to cover the potential range of the CW27 antenna. Here are plots from both antennas.

CW27 with cursers at 2:1 points, or as close as I could get them. 2:1 points are 26.6MHz at the low end to 31.6MHz at the high end for 5.0MHz BW.



CW27 best VSWR frequencies are 27.2MHz and 30.8MHz.




CW27 worst frequency between band edges (red cursor) 28.3MHz @ 1.61VWSR.



Larsen NMO27 2:1 limits for this antenna on this mount on this vehicle 26.0MHz low end, 27.2Mhz high end for 1.2MHz BW.



NMO27 best VSWR on this vehicle, this mount, 1.05:1 at 26.6MHz



As you can see the Larsen NMO27 was tuned on another vehicle and VSWR changed quite a bit on our test vehicle. We didn't notice this until very late in testing after lots of time spent reminiscing, telling stories, discussing the worlds problems, etc. You know, the important suff. And it was lunch time, so we didn't retune the antenna or retest at the Larsen's tuned frequency. Sorry.

What this means is, I am not certain how much degradation there is/was on the Larsen NMO27 due to being about 2.0:1 VSWR at our test frequency. It may be nothing or it may be some, but I don't think its a lot or even close to the 2dB difference we measured in gain between antennas. We won't know until its tested again and I don't plan on that this week or any time soon. Unless one of us wants to drive in LA traffic for hours to do this all over.

In conclusion we learned a lot about each antenna and I believe the Laird CW27 is a fairly efficient antenna and coupled with its 67.5" length has more gain than a Larsen NMO27 with its 52.5" height and the longer antenna wins. Not to mention the thick and delicious wide band width of the Laird CW27, that thing covers from below CB ch1 into the lower VHF low commercial/military band and everything in between.

Many, many thanks to K6GBW for making the trip to my location and supplying the test vehicle and Larsen antenna!

 

[slowmover]

Thank you both for your efforts. .

 

[RFI-EMI-GUY]

Thank you so much! Amazing plots. The CW27 is definitely a winner. How do we convince Laird to put it back into production?

 

[prcguy]

Thank you so much! Amazing plots. The CW27 is definitely a winner. How do we convince Laird to put it back into production?

Place an order for 10,000 units?

 

[RFI-EMI-GUY]

Place an order for 10,000 units?

Maybe a few hundred for resale?

 

[K9KLC]

Thanks you guys for taking the time to do the testing. Much appreciated.

 

[RFI-EMI-GUY]

I recall a couple folks buying the CW27 and then being miffed that the tuning setscrews were loc-tite'd !!!

The engineers and production really nailed it on the head with these. I will try to call Laird to see if they will turn up production. Maybe they have some loading coils in the warehouse? If no joy, I wonder if the patents for this antenna have run out? I would happily throw some bucks into R&D.

The market is limited to basically rogues like us and bootleggers working the entire band with export radios. I don't know if there can be mass appeal to Hamsters and truck stop denizens. It might have to have a flashing LED array or something to attract from the current mediocre products.

 

[K9KLC]

I don't know if there can be mass appeal to Hamsters

A "few" of us maybe...😁

 

[K6GBW]

Does anyone have the Laird C27 antenna? That series is still available and I'd love to see how it stacks up. The Antenna Farm has the whole line up.

 

[Chris155]

I have a laird cb27 & laird hood lip mount, I’ll be installing them on 2015 infinity qx60. This will be a compromise install, it will be our family’s main city & parking garage vehicle.