IC-R75 Sensitivity in New England

[usukICOMuser]

Hi!

I currently live in central New England with an IC-R75 attached to a 33-foot random-wire antenna, stretched alongside the rear exterior wall of my house. I also use Ham Radio Deluxe for PC-based tuning. The first evening I tried the setup, I logged roughly a dozen international stations, including Radio Bulgaria, Voice of Russia, and All India Radio (the latter actually a new one for me, since AIR was normally a little beyond the reach of my previous receiver, a Sony ICF-SW7600GR). However, in the week since, I have been unable to intelligibly receive most non-US HF stations (with the very spotty exception of Spain).

Thoughts on this predicament? Could there be a problem with my setup? Or, as I suspect, just a propagation/weather issue?

Many thanks!

 

[ka3jjz]

It's hard to diagnose this, really. Propagation could be the issue here, or (although unlikely) something might have gotten zapped in the radio.

Right now the flux levels are on the rise so conditions are starting to improve a little. You might also look into a longer or better antenna - 33 foot is pretty small, and won't be very effective below 7 mhz or so. In the Northern hemisphere, we're in the winter months, so propagation on the lower freqs is usually better than higher. This too can be playing a role.

best regards...Mike

 

[Hooligan]

Regardless of any other issues, getting the antenna away from from house & out into relatively free-space should help.

Keep in mind:

Moving the antenna into free space is generally a good thing, but can change the directionality of the antenna.

International stations aren't always a good indication of setup performance unless you also know where the transmitter is at, power levels, signal pattern, etc. For example, getting a great signal on the Voice of Russia isn't all that impressive if it turns out the transmitter they're using is in Cuba & beaming the signal to North America using 500KW.

Sometimes a better way of getting a feel for antenna performance can be to just tune in a variety of amateur radio stations on the various ham bands & listen for them to say where they are & what setup they have.

 

[ridgescan]

Could have been weather local to your 20, or the noise floor could've been higher-burying your weaker DXs, etc.
can you put a 50' wire up? 33' will not do great at lower HF as a randomwire if you're after those longer distances. I run a 50-footer here but it's 40' up, I'm at the coast, and 500' above sea level so all that works in my favor.
Plus I'm grounded, which lowers my noise somewhat.

 

[usukICOMuser]

Many thanks for your excellent suggestions and assistance!

On the antenna issue, I think I should, then, go ahead and extend the random wire length to 50'. As for signal gain, I discovered that much of the problem was due to a very, very poorly-shielded AC laptop adapter that added as much as 25db of noise throughout the entire spectrum (many of the signals were there, but completely washed out from the noise floor). I'll try to move the receiver as far away from RF interference as possible.

 

[ka3jjz]

Even 100 foot will work much better - resonance for this would extend down past 3 mhz, or the 90m tropical band...and our HF antennas wiki (click on the blue text - it's a link) has a great many more designs as well.

You might also consider putting a 9:1 transformer (a.k.a magnetic longwire balun) on the leadin to cut the noise pickup. Another thing to do, aside from replacing that noisy transformer (which you should do anyway) as a stopgap would be to wrap a choke as close to the transformer as possible. Wall warts are famous for being RF radiators - no bloody RF shielding around them at all.

Again, the HF antennas wiki has a few commercial designs for 9:1 transformers, and you can make them yourself - the Shortwave SWL antenna Yahoo group has a lot of technical data in its files area.

I'm willing to bet some R75 owners have ditched the wall wart for a 3 amp non-switching power supply - such a supply would run very cool (according to the specs, max current drain is around 1.1 amp) and reliably for a long time

73 Mike

 

[majoco]

Get the frequencies for the various Volmet broadcasts around the world and use them as propogation clues.

Evenings are good for me to get NY on 6604 and Shannon on 5505kHz.

I get little from Asia unless I stay up late! Winter is better for the same reason - gets dark ealier!