Another long wire question - SW receive only - UK Vintage Radio Repair and Restoration Discussion Forum

6SN7WGTB · Today, 7:41 pm

I have a SONY ICF-SW7600, which I've recapped. It seems to perform well, and I have been experimenting with an external longwire antenna for SW. I have no specific band of interest, just general 2-20MHz.

I've about 25 yards of insulated wire about 10 feet off of the ground. Currently it enters via an open window and runs direct to the external antenna input. I know that this is sub-optimum, but as a proof of concept it's bringing in more stations under the right conditions. Yes, it also brings much more noise too.

Until now, the 'earth' has been internal to the building and a central heating pipe. Again I know not ideal, but one step at a time.

I have a cheap Howe ATU which can actually improve things. I've experimented with a VNA to see how it 'peaks' the desired frequency and done a table of ATU settings to freq. This too is no doubt sub-optimum as the VNA is 50? and the receiver probably not. But roughly-roughly it does seem to peak the signal tuning. (The antenna input schematic is attached).

Given that it does 'work' and does bring in more stations (I can get Radio Thailand in SE UK), I've moved the earth outside, added a coax to bring the antenna 'inside' to the radio. This significantly reduced the background noise - measured simply on headphone jack with RMS AC VM between stations.

But I'd like to do better, within the limitations of what I can install.

I have read what feels like a gazillion posts on aerials/antennae.

So, long intro, but my questions are:
1. Should I add a buried counterpoise? About what proportion of longwire length? I'm assuming I can use insulated 1.5mm^2. The 'end' can be either insulated, or not depending on what is better.
2. Should I be using a 9:1 or so unun?

On 1, I can probably add only one without becoming unpopular, and broadly 'underneath' the longwire. So not 15-20 fanning out radials!

A smallish detail, but the longwire drops to ground level where I have the unun or connection to the inbound coax. I cannot drop it at the far end and bring back via coax, which I believe would be better - yes, so the 'L. is at the less ideal end.

Thank you.

paulsherwin · Today, 8:00 pm

Others may have a different view, but I'm not sure it makes sense to put a lot more effort into aerial design and matching with a 7600. You've already done the basic stuff. These are very competent radios, but they were never designed to be static comms receivers for SW use. If you're really serious about SW reception, it may be a better idea to concentrate on getting a proper comms receiver, either vintage or modern.

GMB · Today, 8:46 pm

Yes, the normal complexities are to match a transmitter that is very picky about what it drives. Receivers can sometimes work better with crappy aerials especially if the aerial is more crappy at picking up local QRM than the actual signals.

Important point: if you bring an actual earth into a house then bear in mind, especially with PME supply, it can be a dangerous voltage during fault conditions relative to things in the house that are connected to mains safety earth (including pipes). Also, join them together and you risk huge current flowing.

Today, 7:41 pm	#1
6SN7WGTB Hexode Join Date: Apr 2021 Location: Crawley, West Sussex, UK. Posts: 443	Another long wire question - SW receive only I have a SONY ICF-SW7600, which I've recapped. It seems to perform well, and I have been experimenting with an external longwire antenna for SW. I have no specific band of interest, just general 2-20MHz. I've about 25 yards of insulated wire about 10 feet off of the ground. Currently it enters via an open window and runs direct to the external antenna input. I know that this is sub-optimum, but as a proof of concept it's bringing in more stations under the right conditions. Yes, it also brings much more noise too. Until now, the 'earth' has been internal to the building and a central heating pipe. Again I know not ideal, but one step at a time. I have a cheap Howe ATU which can actually improve things. I've experimented with a VNA to see how it 'peaks' the desired frequency and done a table of ATU settings to freq. This too is no doubt sub-optimum as the VNA is 50? and the receiver probably not. But roughly-roughly it does seem to peak the signal tuning. (The antenna input schematic is attached). Given that it does 'work' and does bring in more stations (I can get Radio Thailand in SE UK), I've moved the earth outside, added a coax to bring the antenna 'inside' to the radio. This significantly reduced the background noise - measured simply on headphone jack with RMS AC VM between stations. But I'd like to do better, within the limitations of what I can install. I have read what feels like a gazillion posts on aerials/antennae. So, long intro, but my questions are: 1. Should I add a buried counterpoise? About what proportion of longwire length? I'm assuming I can use insulated 1.5mm^2. The 'end' can be either insulated, or not depending on what is better. 2. Should I be using a 9:1 or so unun? On 1, I can probably add only one without becoming unpopular, and broadly 'underneath' the longwire. So not 15-20 fanning out radials! A smallish detail, but the longwire drops to ground level where I have the unun or connection to the inbound coax. I cannot drop it at the far end and bring back via coax, which I believe would be better - yes, so the 'L. is at the less ideal end. Thank you. Attached Thumbnails __________________ Richard \| BVWS & RSGB member \|

Today, 8:00 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Another long wire question - SW receive only Others may have a different view, but I'm not sure it makes sense to put a lot more effort into aerial design and matching with a 7600. You've already done the basic stuff. These are very competent radios, but they were never designed to be static comms receivers for SW use. If you're really serious about SW reception, it may be a better idea to concentrate on getting a proper comms receiver, either vintage or modern.

Today, 8:46 pm	#3
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,095	Re: Another long wire question - SW receive only Yes, the normal complexities are to match a transmitter that is very picky about what it drives. Receivers can sometimes work better with crappy aerials especially if the aerial is more crappy at picking up local QRM than the actual signals. Important point: if you bring an actual earth into a house then bear in mind, especially with PME supply, it can be a dangerous voltage during fault conditions relative to things in the house that are connected to mains safety earth (including pipes). Also, join them together and you risk huge current flowing.