What would Sherwood invest in?

“Hi,

Just a thought – something to add in your next advert regarding the IC-8600.

‘Today, we’ve just received IC-R8600 which has been out of stock for almost a year. If you are an SWL looking for one, you know what we’ve got. And if you are asking yourself ‘why would anyone in the world pay that much for just a receiver…?’

Maybe because it’s also the highest performing wideband receiver according to the internationally respected Sherwood Engineering Receiver Test Data List !  (Number 5 in the list of best performing receivers overall)

http://www.sherweng.com/table.html

Regards,

Ben.”

Hi Ben,

Thank you for your feedback. I am sure ICOM is loving it – and so am I. Having in stock the top ranked wideband receiver on Sherwood’s list is something to be proud of!

I am not an expert, merely an amateur operator. However, every now and then I too ‘check’ the list of radios which are tested by Sherwood Labs. As you’ve said, the list has been around since the early days of the internet and it is regarded as an authority on the receiving capabilities of classic and modern radios.

It is important to point out that list was created for rating a very specific parameter: Third-Order Dynamic Range Narrow Spaced – or – ARRL RMDR (Reciprocal Mixing Dynamic Range).

Bob Sherwood explains this from a very practical perspective, writing to amateurs like myself:

“Dynamic Range:

Now we get to the nitty gritty. I started testing radios in 1976 because the ARRL rated the Drake R-4C very good, but in a CW contest it was terrible. The radio overloaded in a CW pile-up, so I decided to figure out what was wrong with their testing. In 1975, the League had started testing for noise floor and dynamic range, new terms for most amateurs. Spurious Free Dynamic Range measures how the radio can handle strong undesired signals at the same time as a weak desired signal, without overload. When a radio overloads, it starts generating spurious signals on its own.

Dynamic range is defined as the level in dB when two strong test signals make distortion in the radio equal to the noise floor. The radio thus can handle that range of signals before the strong signals just start to overload the radio.

The League originally only tested the dynamic range at 20kHz test spacing, which was reasonable at the time. But as multi-conversion radios became the norm, this test was inadequate. The Drake example was a case in point. When the two test signals are 20kHz apart, the overload distortion products are 20kHz each side of the pair of test signals. In other words, the League was testing as if the QRM was always going to be 20 and 40kHz away! In reality the QRM is likely going to be close by.

In 1977 I published an article in “Ham Radio Magazine” discussing this subject. I tested the offending R-4C at 2kHz in addition to 20kHz. In that case the 20kHz dynamic range was over 80dB, but the 2kHz dynamic range was less than 60dB.

The roofing filter of the R-4C is 8kHz wide, and in a CW contest, there were many signals inside that 8kHz filter, overloading the radio. I installed a 600Hz roofing filter in the R-4C, and the problem went away. When testing the Sherwood modified R-4C at 2kHz, the dynamic range was over 80dB, just like it was with the 20kHz test.

Most radios in the 70s and 80s had gone to up-conversion for two reasons. This got rid of the necessity of a pre-selector, and it allowed general coverage without a dead spot equal to the first IF frequency. In the up-conversion radio, the first IF was always above 10 meters, and often above 6 meters. All first IF filters were at least 15kHz wide, and there was the problem. The Drake 8kHz first IF was bad enough, and now almost all the radios for 20+ years had a first IF what was at least 15kHzwide. Almost all of them had a close-in dynamic range around 70dB. That was barely adequate for SSB and inadequate for CW.

For more than 40 years I have been testing radios, and I decided to sort the table on my website by close-in dynamic range at 2kHz spacing. This was the “acid test” for CW contest / DX pile up operation.

In 2003 the Ten-Tec Orion came along, and it went back to a 9MHz first IF (instead of 40 to 70MHz), and offered a narrow CW roofing filter, like I had added to the Drake. It was the first commercial rig to be better than the Sherwood roofing filter modified R-4C. Later the Elecraft K3 came to market, and now Yaesu and Kenwood have what is now called “down-conversion” radios with a low frequency first IF.

What do you need in the way of close-in dynamic range? You want a number of at least 70dB for SSB, and at least 80dB for CW. A 10dB safety factor would be nice, so that means you would prefer 80dB for SSB and 90dB for CW. Now there are approximately 20 radios that meet that specification.”

To sum it up: Bob is primarily looking at the problem from a CW / SSB contester or DXer surrounded by hundreds of high power transmitters in close proximity. A typical North American environment – or even worse, ‘every contest weekend’ in Europe. If you haven’t tried it – it is an absolute must: the feeling of frustration not being able to hold a frequency on 40m running 5kW into a full size 3el rotary Yagi. Europeans are crazy; imagine having two 50kW Italians running 2kHz above and below you! These are incredibly harsh conditions and a challenge for any modern receiver.

Luckily, not our case, where 99% of fellow competitors are 7,000 – 12,000km away.

Would you rather have a K3 which ranks higher RMDR on Sherwood list than IC-7851 or Hilbering PT-8000A?

I certainly wouldn’t – for the same reason one wouldn’t buy a car with the lowest fuel consumption or certainly not one ranked as the fastest in the world. Sherwood ranking is simply a ‘single parameter’ list.

If the Yaesu FTdx-101D MP is indeed the best radio on the market, according to Sherwood’s list, would you not then except that Bob Sharwood’s own shack would feature nothing else but a line of 101’s? That’s what I thought.

“The (Bob Sherwood’s) shack picture is of operating position #1 which is an IC-7610 and an Alpha 99, Ops #2 is a Kenwood TS-990S and whatever rig I am evaluating, driving an Alpha 89. Ops #3 is my backup HF station and 6 meters with an ICOM 7610 driving an ACOM 1000. The IC-7300 drives a Monitor Sensors 630m transverter.”

Two IC-7610, IC-7300, Kenwood 990 and IC-R8600 receiver!  

In his very introduction to ‘Sherwood list’, on the subject of noise floor measurement, Bob gets straight to the core:

“Noise floor measures how weak a signal one can hear. Practically it is only of significance on the higher HF bands due to the higher level of band noise on the low bands. This assumes you are listening on your transmit antenna. If you are using a Beverage or a low gain loop, then it could be an issue on any band.

The noise floor is measured with a 500Hz CW filter band width, assuming the radio has a CW filter. There is a note on the measurement if the radio only had an SSB bandwidth. Older radios (Drake, Collins) had no switchable preamp. Compare them to a modern radio with Preamp ON or Preamp #1 ON. A noise floor of -135dBm is more than adequate on 15 meters in a quiet rural location. A lower noise floor (-138dBm) might be useful on 10 meters in a quiet location. Serious 6 meter DXers often use an external low noise preamp to get the noise floor down to -140dBm or a few dBm lower. If you are in the city, hardly any of this matters due to all the local noise. (On 15 – 6 meters, hardline would be important to reduce the feedline loss to make the best use of the noise floor.)”

In other words, lab tests are lab tests – in reality, your location and external interference are the predominant factors, far more important than a radio itself.