That hum - NOT amateur radio

A fair proportion of people say they can hear a very low frequency audio hum. I can hear it. I have heard it from very early morning (about 5.30am UK time) until now. At first I thought it was someone's washing machine, or perhaps a plane.

Could it be the distant noise of traffic? Low audio frequencies may propagate through rocks. It is a very low level, but definitely there. It is worse today than I recall. Weather conditions are a little misty and we can sometimes hear traffic on the A14 road (about 2 miles away) clearly on misty days, which must allow audio signals to propagate further. Normally we do not hear A14 traffic.

I expect someone could "see it" with suitable audio transducers and software.

Polyakov mixer and 50Hz hum

There is something strange about my Polyakov mixer based direct conversion receiver for 28.1246MHz WSPR at the moment.

On the bench, when connected to a 50 ohm signal generator or sitting on the bench without an antenna connected, the background noise is a quiet hiss. With an earpiece in a quiet room I can just hear a -125dBm signal, even without an RF preamp: it is a good, sensitive and simple design.

However, the moment I connect my outside halo antenna via a coax to the (unscreened) breadboard RX the 50Hz hum level is quite high, certainly some 40dB higher audio than the MDS signal. This is with the RX run from a small sealed lead acid battery. With a mains supply I might expect some hum, but what is going on? Why the high hum pickup?

My coax antenna feed passes through the loft and then outside passing plenty of mains cables, so I must be inducing some 50Hz pick-up on the coax outer which is coupling into the copper laminate breadboard ground plane. A tidy rebuild will be needed before I could put the RX into a screened box.

I do not recall having a similar problem with other DC designs I have tried (single balance diode pair, NE602, SBL1 etc.) when used in a similar lash-up breadboard.

Anyone any suggestions?

FT-450D hum: a good response from Yaesu

Last night I wrote to Yaesu UK about the FT-450D hum issue and got a very fast and very helpful, response from Paul Bigwood their Technical Sales Manager. All credit to him.

I will paraphrase Paul's reply below.

He confirms the hum problem has been recognised and that it doesn't affect all radios. Those it does, are only affected in voice modes, when the display brightness is reduced below its normal maximum level. The level of hum is generally low and is usually only noticeable when the received signal strength is high [i.e. with local stations], DX stations don't normally hear it.  He says that steps have been taken to resolve the issue and product shipping into the UK dealers since the beginning of the year have a modification to resolve it. He told me that if I purchased one that does suffer from hum under the circumstances as above, then it can be returned to Yaesu for updating under warranty.

He went on to say,

"Please rest assured that Yaesu does care about its products, their reliability and performance. We certainly look to resolve any problems as soon as they become known to us.  The FT450D is a splendid radio, having done excellently at the T32C DXpedition last year when over 200K QSOs were made with no reports to us of any hum problems."

I thought this was an excellent and totally professional response. Yaesu is a first class manufacturer and it is reassuring to see they have taken on board the hum issue in this otherwise excellent little radio and have now taken steps to properly fix it on new build units.

FT-450D Hum (again)

From what I see and hear, Yaesu is still selling this otherwise excellent HF/6m transceiver with a fundamental design flaw: hum created by poor grounding of the display module when dimmed from maximum brightness. This problem was there on the FT450 but whatever improvement, if any, was implemented in the upgrade to the D version,  it has not worked consistently.  This really annoys me: surely this sort of issue should have been picked up in beta testing? The fix being implemented by many owners seems simple, so why the heck doesn't Yaesu get on a fix it?

FT-450D hum?

Although usually/mostly a QRP operator, I've been considering an update to my main station transceiver since selling my 10W IC703 to a local friend. One possible candidate rig is the 5-100W Yaesu FT-450D. It is getting very good reviews with excellent comments on its  receiver features. For a "full feature" HF/6m radio it is good value for money.

But, I am bothered about one thing: many reviews and comments on the FT-450D Yahoo group confirm a design issue with TX hum, believed to eminate from the poor grounding of the display unit. Nothing I've seen or heard has convinced me this widely reported issue has yet been properly fixed by Yaesu. This is not a problem with the display set to its brightest setting, but should one pay around £800 for a radio with a fundamental design issue not solved in a recent upgrade? No.  A question to Waters and Stanton asking if Yaesu has fixed it has not received a reply yet after 2 days: I suspect they don't want to say "no". I have said that if it hums it would be returned.  So, until I hear the problem has been resolved my "buy" decision is on hold. I am in no great hurry.